31 August 2009
There were several recent news announcements of the EADS Astrium "Gravity Tractor" concept. This may be based upon a previous design developed by this EADS AStrium, the APEX or APophis EXplorer. Here is the abstract about the EADS Astrium "Apex" which was not specifically a gravity tractor mission but a radio beacon mission. Perhaps this was redesigned to be a gravity tractor spacecraft. Both systems seem to employ electric propulsion.
From an abstract presented at The First Meeting of The International Primitive Body Exploration Working Group (IPEWG), January 13-16, 2008, Bankoku Shinryokan, Okinawa, Japan:
APEX: A MISSION CONCEPT TO EXPLORE THE PHYSICAL PROPERTIES OF ASTEROID APOPHIS AND THEIR IMPACT ON ORBITAL EVOLUTION
Christian Trenkel (Astrium Ltd, Stevenage, UK), Paolo d’Arrigo (Astrium Ltd, Stevenage, UK), Simon Barraclough (Astrium Ltd, Stevenage, UK ) and Andrea Carusi (IASF, Rome, ITALY) [Contact E-mail : email@example.com]
On April 13th 2029, asteroid Apophis will have a close encounter with Earth, which could send it on a collision course with our planet, in 2036. The close encounter means that even a small shift in Apophis’ position in 2029, of the order of a few km, completely changes the outcome in 2036.
The orbit of Apophis is subject to a number of gravitational and non-gravitational perturbations, some of which are currently known with limited accuracy. These uncertainties are then amplified by the orbit propagation process and result in significant errors in position determination at the time of the close passage in 2029.
In late 2006, the Planetary Society issued the Apophis Mission Design Challenge, inviting the public to design a mission that would reduce the 3σ uncertainty in the position of Apophis in 2029, based on measurements taken by 2017, to about 14km. Astrium Ltd, UK, leading an international team, have submitted the APophis EXpress (APEX) proposal in response to this challenge.
A sensitivity analysis shows that the orbital parameters of Apophis need to be determined to equivalent absolute position uncertainties of a few metres, and absolute velocity uncertainties of around 0.2mm/s. Standard Radio Science Experiments (RSE) can achieve this accuracy, provided that all systematic effects and forces are adequately modeled. For Apophis, a complex non-gravitational force, the Yarkowski Effect (YE), can shift its position by over 100 km between 2017 and 2029. To meet the requirements, the YE needs to be determined with an accuracy of a few percent.
Analytical YE models exist only for a few special cases. A numerical model of the YE, based on in situ measurements of the relevant – mainly thermo-optical – asteroid properties, is therefore essential to reach the required accuracy. It is concluded that the successful orbit determination for Apophis is conditional upon a determination of its physical properties with unprecedented precision.
The APEX mission achieves this through the most detailed and extensive investigation of an asteroid ever performed. An orbiter, instrumented with a sophisticated remote sensing payload, will study Apophis for three years, from its arrival in early 2014 to early 20217. High resolution visual and thermal mapping campaigns will be followed by a RSE, with the ultimate goal of determining the orbital elements to parts per billion. These experiments will be repeated several times during the first year, in order to consolidate and complete the models used for orbit determination. The second and third year will be used to verify the accuracy of the orbit determination, and also allow time for additional mapping campaigns if necessary.
The relatively low gravity of Apophis (compared e.g. to Eros) represents a multiple challenge:
• The orbiter motion is influenced, to an unusually high degree, by non-gravitational forces. This results in most orbits being unstable. In addition, these forces have to be modeled, or directly measured, to very high accuracy.
• For remote sensing, ground track speeds tend to be very low (cm/s), making global mapping a slow process with standard orbits.
To meet these challenges, during radio science the APEX spacecraft is placed in the only stable low-altitude orbit around Apophis: a terminator orbit with the spacecraft keeping a constant cross section to solar radiation. This allows long manoeuvre-free periods when the spacecraft orbit can be tracked from Earth with great accuracy. Simultaneously, an on-board accelerometer is used to measure all non-gravitational perturbations. Finally, high resolution global mapping is achieved relatively quickly thanks to a forced fast orbit around Apophis, using the spacecraft’s own solar electric propulsion system to generate “artificial gravity”.
Link: Final Program and List of Abstracts: First Meeting of The International Primitive Body Exploration Working Group (IPEWG)
Link: EADS Astrium Press Release on APEX asteroid mission
A recent presentation from Eileen Collins to the NASA Advisory Council (NAC) that includes a section on human asteroid missions. Here are some points made in the presentation regarding NEOs.
Link: Florida Today Article
Link: Presentation from Eileen Collins (Space Operations Committee) to NASA Advisory Council: 16 July 2009
30 August 2009
Scientists design spacecraft to save Earth: A spacecraft capable of saving the world from a catastrophic asteroid collision has been designed by British space scientists.
Richard Gray, Science Correspondent
29 August 2009
Heroic missions to stop life on Earth from being wiped out by an asteroid have become a favourite theme for Hollywood disaster films.
Now, a team of British engineers have designed a real-life spacecraft to save the world from destruction.
Their invention, called a "gravity tractor", would be deployed when an orbiting rock is detected on a collision course with Earth.
The spacecraft would intercept the asteroid and position itself to fly alongside it, just 160ft from its surface.
From this position, the 10 tonne craft is able to exert a small gravitational force on the rock, pulling the asteroid towards it.
By gradually modifying its course, over several years, the gravity tractor is able to slowly shift the asteroid's trajectory enough to ensure it misses the Earth.
Details of the planned craft come just weeks after an asteroid or comet was found to have ploughed into Jupiter, which is a giant gas planet, leaving behind a vast impact scar – estimated to be about the same size as the Earth – in its atmosphere.
Scientists believe it is only a matter of time before an asteroid comes close enough to the Earth to be a threat.
Nasa, the US space agency, is so concerned that it has established an expensive monitoring programme to track every object in the sky that might come close to the planet.
It estimates there are more than 100,000 asteroids orbiting near the Earth that are large enough to destroy a city. So far the agency has only been able to identify and track 6,363 of them.
Just one football pitch-sized asteroid would be capable of obliterating a large city and could cause widespread destruction by also throwing flaming material into the atmosphere and triggering tidal waves.
In 1908, a meteor of this size exploded above Lake Tunguska in Siberia, destroying 770 square miles of forest. Such collisions hit the Earth every 100 years.
To avoid such a disaster, engineers at space company EADS Astrium, which designs and builds spacecraft for Nasa and the European Space Agency, have designed the gravity tractor.
The team, who are based in Stevenage, in Hertfordshire, believe the craft could divert asteroids that are up to 430 yards across – big enough to release 100,000 times more energy than the nuclear bomb dropped by the United States on Hiroshima in 1945.
"Anything bigger than 30m (32 yards) across is a real threat to the Earth," said Dr Ralph Cordey, science and exploration business development manager at Astrium.
"Unfortunately it is a matter of when rather than if one of them hits us.
"The gravity tractor exploits the principals of very basic physics – every object with a mass has its own gravity that affects objects around it. It can move fairly large objects 300 metres (984ft) to 400 metres (1,312ft) across.
"These asteroids are hurtling around our solar system at 10km per second, so when you scale that up, you just need a tiny nudge to send it off course."
The 30m gravity tractor would need to be launched around 20 years before an asteroid is due to the hit the earth, giving it enough time to intercept the asteroid as it orbits the sun and change its trajectory.
The spacecraft would use four highly efficient low energy thrusters – known as ion thrusters which are often used on deep space probes – to gradually shift its position as it flies above the rock, causing the gravitational pull it has on the asteroid to "tug" it off the collision course.
With an asteroid around 300 yards across, the gravity tractor changes the angle it is travelling in by a fraction of an inch over a period of 15 years, creating enough of a change in the orbit for the asteroid to miss the Earth.
The team have designed the gravity tractor and planned the details of the mission. The craft could be built in a relatively short time, using existing technologies, if an asteroid was detected on a collision course.
It is likely it would require an international agreement to send a mission into space.
Christian Trenkel, who worked on the mission plans, said: "We have designed the mission using the technology that we currently have available, so it could be put into practice at any time."
Earlier this year, Nasa published a feasibility paper on using a gravity tractor to steer an asteroid, or near earth object as they are called, away from the Earth. It concluded that with enough warning it could be highly effective.
In 2004 an asteroid known as Apophis caused concern after it was calculated to pass alarmingly close to the Earth.
Projections of its path around the sun predicted it had a one in 37 chance of hitting the planet in 2029 – the highest threat in recorded history.
The threat of a 2029 collision was later ruled out but scientists fear that the asteroid could still pass through a key point in space known as a "keyhole" that would put it on course to collide with the Earth in 2036.
Kevin Yates, project manager for the UK Near Earth Object Information Centre which is responsible for warning UK ministers of risks from asteroids and comets, said: "Gravity tractors are a solution that are growing in popularity.
"There does need to be international agreements on how to tackle a threat from an asteroid.
"There are all sorts of political difficulties if, for example, a mission only managed to move the point of collision on the Earth from one country to another."
Link: Telegraph Article
27 August 2009
20 August 2009
August 20, 2009
NASA Wants $800M More for Asteroid Search
City College of New York physics professor Dr. Michio Kaku and Spaceworks Commercial President A.C. Charania on NASA's effort to discover and track asteroids.
Link: Fox Business Network
20 August 2009
From the article...
How our solar system was formed has fascinated scientists and laymen alike for — well, for a really, really long time. New research may have answered a piece to the puzzle – how big were the first planetesimals?
For those of you scoring at home,” planetesimals” were the first solid objects in our newly minted solar system (also known as the protoplanetary disk). They began life as small grains of dust orbiting an infant sun. These grains would bump into each other, clump together and gradually form larger grains of dust, which eventually became small space rocks.
Now the theory goes that some of these small rock-sized planetesimals aspired for greater things, and continued to gradually grow in size to become asteroids, and that a few of those continued to grow beyond the asteroid stage and become planets.
The problem with this tidy little theory is that when the burgeoning space rocks grew to about one meter (3.3 feet) in size, orbital mechanics tells us the gas comingling with them in the protoplanetary disk should have acted like a brake, slowing their velocity appreciably. Their orbital speed having been cut, these filing cabinet-sized space rocks would have spiraled into the sun. Essentially, the gas would have acted as a celestial “mini-vacuum.” The problem is, there are asteroids up there in space. Honest, ask any astronomer. So what happened?
Evidence is now mounting that these small space rocks quickly “jumped” (or grew) in size from below one meter to multi-kilometer in size. Planetesimals that big were big enough to plow through the drag created by the gas in the protoplanetary disk without having their orbits appreciably altered. Hence they did not spiral into the sun.
What data point to a jump in asteroid sizes? Simply, the asteroids available for viewing in the night’s sky. Telescopic surveys indicate there is currently a plethora of asteroids less than one kilometer (.62 mile) wide but those over one kilometer drop considerably in number. The authors used computer simulations in an attempt to mimic the impacts and coagulation processes that took place over the millions of years between when the asteroids formed and now. The only way they could arrive at the current asteroid size distribution was to begin these simulations with planetesimals that quickly morphed into asteroids hundreds of kilometers in size. Once their growth spurt was over, these massive celestial bodies began an epoch-sized game of demolition derby as they orbited the sun. Over the eons, and with each extraterrestrial pileup, came fewer and fewer large asteroids – a fragmentation process that continues to this day. Despite the modest sizes of asteroids today, the paper’s authors conclude that asteroids must have been born big.
The paper, “Asteroids Were Born Big” is available now online from the ScienceDirect website and will be available in a future edition of the journal Icarus.
Link: SpaceFellowship Article
19 August 2009
18 August 2009
Link: Lockheed Martin Video
From the article..
Dual Orion capsules studied for manned asteroid missions
17 August 2009
A manned asteroid mission using two Orion spacecraft, docked nose-to-nose to form a 50-ton deep space vehicle, is being studied by Lockheed Martin Space Systems as an alternative to resumption of U.S. lunar landing missions.
The Orion asteroid mission concept is being unveiled just as the Presidential committee reviewing U.S. human space flight is citing asteroid missions after 2020 as a less costly alternative to NASA's proposed lunar landing infrastructure. Results of the review will be briefed to President Obama by Norman Augustine, committee chairman, by the end of August.
The docked Orion configuration as shown in a Lockheed Martin graphic (above) would have a total of four large solar arrays and two service modules as well as two command modules for extra space on the several week flight. Single 25-ton Orion spacecraft would first be used to replace the space shuttle for servicing the International Space Station. But use of them for asteroid missions and other deep space sites would maximize utilization of the Orion system if lunar landings are deleted as a near term goal.
If one looks closely at the graphic, a space suited astronaut deployed from the Orion, is standing atop the asteroid. The graphic is from a Lockheed Martin promotional movie that shows concepts under study by the Orion prime contractor.
Under the Bush Administration strategy, NASA had planned a resumption of lunar landing missions by about 2020 using the Orion as a lunar orbiting command ship while its crew descended to the moon in Altair landers for lengthy stays on the surface.
The official NASA line has been solidly "all moon" for the last several years, while more realistic assessments over the same period have shown that is not feasible. NASA more recently, however, had become more open about an asteroid mission capability for Orion after space scientists and planners meeting before formation of the committee began to criticize the lunar goal as too fragile.
Development and cost problems with the Ares 1 and Ares 5 launch vehicle programs have also become increasingly apparent since about 2007.
Augustine and other committee members such as former astronaut Sally Ride have already reported publicly that NASA's current plan to retire the shuttle, finish the space station and return to the moon by the early 2020s is not even remotely feasible under NASA's current funding profile.
Orion missions to asteroids would be useful to characterize and sample them. This would be important as early preparation to use some yet undetermined system if the need ever arose to divert an asteroid to save Earth from a devastating impact. Some asteroids are solid bodies, while others are rubble piles of loose rock, making samples and close up characterization useful for diversion studies that would differ depending upon the type of asteroid threatening Earth.
In fact a Lockheed Martin video titled "Orion For Crewed Science Missions" shows the twin Orion configuration closely orbiting an asteroid while space suited astronauts explore its surface. With the minuscule gravity of an asteroid, astronauts flying manned maneuvering units could travel between the Orion combo and the object without ever requiring a much heavier, and expensive, asteroid landing vehicle.
The video, little noticed at the time, was shown in early August at a propulsion conference in Denver sponsored by the American Institute of Aeronautics and Astronautics. The AIAA "Joint Propulsion Conference" so called because it brings together multiple international agencies often makes news as it also did in 2008 when Chinese researchers openly discussed their scramjet technology program.
At this year's event, the Lockheed Martin video was part of a presentation delivered by former astronaut Brian Duffy, now Lockheed Martin vice president and program manager for the Altair lunar module part of the Orion lunar landing infrastructure.
Duffy's presentation also cited satellite servicing that could be performed by astronauts from an Orion configuration, equipped with a shuttle-type manipulator arm deployed from its service module.
The presentation also discussed use of single Orion spacecraft to service geosynchronous orbit military and civilian satellites and the potential for them to travel to Lagrangian points to service telescopes like the giant new Webb space telescope set for launch in about four years. Lagrangian points balance out gravity from the sun, Earth and moon allowing spacecraft to remain parked at those locations. They are about 1 million mi. from Earth, about the same distance as some asteroids passing near Earth. This means Orions configured for missions to telescopes, like Webb, at Lagrangian points would have a life support capability also generally suitable for asteroid missions.
The twin Orion design includes large service modules on each spacecraft to allow extra space for astronauts to live in. More importantly more capability to carry life support systems for several week missions could be carried in the two service modules.
Link: Spaceflight Now Article
17 August 2009
This novel boldly explores the question: what if, tomorrow, a large asteroid was discovered to be on a course for a collision with Earth with less than one year until impact. Asteroid 20-2012--Sepulveda explores that real tomorrow, not some fanciful future date in some utopian peaceful world, but our tomorrow, with a distracted government addicted to secrecy, locked in a grinding war with the forces of international terror, in a world full of mutually hostile governments. Asteroid 20-2012--Sepulveda masterfully describes the struggles both scientific and private of the asteroid's discoverer, Mexican-American Alicia Sepulveda, whose discovery of the asteroid, and naming it after her family, unwittingly sweeps her into a desperate and deep-black government effort to stop its collision with Earth. She is unknowing also that the secrets of her own past may destroy her there. We also encounter Jade and Blondie, aka Cassandra Chen and Pamela Monroe, nervy news anchors, who in a dark comedy of errors, innocently move their morning show to ground zero, and rename it "Jade and Blondie Watch the Stars." They do all of this in honor of the asteroid that they were told will sail beautifully over Hollywood, when it is actually is going vaporize the entire L.A. basin! But the secret government agents following Pamela know better, as it turns out, for she is also unconsciously being drawn to the secret asteroid impact zone, there to collide with her own dark destiny. For Pamela is her very own walking black program and linked with the asteroid and all it portents. The portrayal of these crises, both cosmic and personal, make this a fast-paced science thriller of the first order.
"Asteroid 20-2012 Sepulveda: The cosmos plays hardball"
Victor Norgarde (Author)
Link: Amazon.com Book Link
12 August 2009
Link: National Research Council Report (Near-Earth Object Surveys and Hazard Mitigation Strategies: Interim Report)
Review of report from Leonard David (SpaceCoalition.com)
Report: NASA Falling Short in Eying Hazardous Near Earth Objects.
12 August 2009
NASA is falling short in its U.S. Congress-assigned sky-watching duties to chart the whereabouts of certain-sized Near Earth Objects (NEOs) that may threaten our planet.
The prestigious National Research Council (NRC) released today a set of interim findings in a two-part study that looks into issues in the detection of potentially hazardous Near Earth Objects (NEOs) and approaches to thwarting identified hazards to our planet.
The NRC appraisal is a congressionally-mandated review of NEOs that orbit the Sun and approach or cross Earth’s orbit.
The committee’s blue ribbon panel of experts has issued five findings:
-- Congress has mandated that NASA discover 90 percent of all near-Earth objects 140 meters in diameter or greater by 2020. The administration has not requested and Congress has not appropriated new funds to meet this objective. Only limited facilities are currently involved in this survey/discovery effort, funded by NASA’s existing budget.
-- The current near-Earth object surveys cannot meet the goals of the 2005 NASA Authorization Act directing NASA to discover 90 percent of all near-Earth objects 140 meters in diameter or greater by 2020.
-- The orbit-fitting capabilities of the Minor Planet Center in Cambridge, Massachusetts are more than capable of handling the observations of the congressionally mandated survey as long as staffing needs are met.
-- The Arecibo Observatory telescope in Puerto Rico continues to play a unique role in characterization of NEOs, providing unmatched precision and accuracy in orbit determination and insight into size, shape, surface structure, multiplicity, and other physical properties for objects within its declination coverage and detection range.
-- The United States is the only country that currently has an operating survey/detection program for discovering near-Earth objects; Canada and Germany are both building spacecraft that may contribute to the discovery of near-Earth objects. However, neither mission will detect fainter or smaller objects than ground-based telescopes.
This interim report addresses some of the issues associated with the survey and detection of NEOs. The committee is continuing to gather information and will produce a final report on a broader range of NEO issues by year’s end.
Link: Space Coalition News Item
Link: Huffington Post Article
11 August 2009
Contact: Rebecca Alvania
National Academy of Sciences
Asteroid detection at NASA
In the 2005 NASA Authorization Act, Congress mandated that by 2020 NASA should be capable of detecting at least 90 percent of objects over 140 meters wide in the vicinity of Earth's orbit. NEAR-EARTH OBJECT SURVEYS AND HAZARD MITIGATION STRATEGIES, an interim report of a congressionally mandated study by the National Research Council, examines NASA's current ability to survey and detect these near-Earth objects. A final report will address hazard mitigation and make recommendations on ways to improve the program.
Reporters may obtain copies of the interim report by contacting the National Academies' Office of News and Public Information, tel. 202-334-2138 or e-mail firstname.lastname@example.org. Advance copies will be available to reporters only starting at noon EDT on Tuesday, Aug. 11. THE REPORT IS EMBARGOED AND NOT FOR PUBLIC RELEASE BEFORE 11 A.M. EDT ON WEDNESDAY, AUG. 12.
Link: Eureka Alert Press Announcement
10 August 2009
From the image reference...
This image, taken as Saturn approaches its August 2009 equinox, shows a shadow being cast by a narrow, vertically extended feature in the F ring.
Imaging scientists are working to understand the origin of structures such as this one, but they think this image may show the shadow of an object on an inclined orbit which has punched through the F ring and dragged material along in its path.
The second (bottom) version of the image has been brightened to enhance the visibility of the ring and shadow. Background stars appear elongated in the image because of the camera's exposure time.
This image and others like it (see PIA11663) are only possible around the time of Saturn's equinox which occurs every half-Saturn-year (equivalent to about 15 Earth years). The illumination geometry that accompanies equinox lowers the sun's angle to the ringplane and causes out-of-plane structures to cast long shadows across the rings. Cassini's cameras have spotted not only the predictable shadows of some of Saturn's moons (see PIA11657), but also the shadows of newly revealed vertical structures in the rings themselves (see PIA11654).
This view looks toward the unilluminated side of the rings from about 27 degrees above the ringplane.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on June 11, 2009. The view was acquired at a distance of approximately 866,000 kilometers (538,000 miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 30 degrees. Image scale is 5 kilometers (3 miles) per pixel.
Link: Cassini Imaging Central Imaging Post
Link: Discover Magazine Blog post
Image credit: NASA/JPL-Caltech
From the NASA/JPL-Caltech News Release...
This artist's concept shows a celestial body about the size of our moon slamming at great speed into a body the size of Mercury. NASA's Spitzer Space Telescope found evidence that a high-speed collision of this sort occurred a few thousand years ago around a young star, called HD 172555, still in the early stages of planet formation. The star is about 100 light-years from Earth.
Spitzer detected the signatures of vaporized and melted rock, in addition to rubble, all flung out from the giant impact. Further evidence from the infrared telescope shows that these two bodies must have been traveling at a velocity relative to each other of at least 10 kilometers per second (about 22,400 miles per hour).
As the bodies slammed into each other, a huge flash of light would have been emitted. Rocky surfaces were vaporized and melted, and hot matter was sprayed everywhere. Spitzer detected the vaporized rock in the form of silicon monoxide gas, and the melted rock as a glassy substance called obsidian. On Earth, obsidian can be found around volcanoes, and in black rocks called tektites often found around meteor craters.
Shock waves from the collision would have traveled through the planet, throwing rocky rubble into space. Spitzer also detected the signatures of this rubble.
In the end, the larger planet is left skinned, stripped of its outer layers. The core of the smaller body and most of its surface were absorbed by the larger one. This merging of rocky bodies is how planets like Earth are thought to form.
Astronomers say a similar type of event stripped Mercury of its crust early on in the formation of our solar system, flinging the removed material away from Mercury, out into space and into the sun. Our moon was also formed by this type of high-speed impact: a body the size of Mars is thought to have slammed into a young Earth about 30 to 100 million years after the sun formed. The sun is now 4.5 billion years old. According to this theory, the resulting molten rock, vapor and shattered debris mixed with debris from Earth to form a ring around our planet. Over time, this debris coalesced to make the moon.
Link: JPL News Release
Link: NASA Multimedia (Planetary Smash Up)
Link: NASA Animation (25 MB .mov file)
Link: CalTech Press Release
ABUNDANT CIRCUMSTELLAR SILICA DUST AND SiO GAS CREATED BY A GIANT HYPERVELOCITY COLLISION IN THE ~12 MYR HD172555 SYSTEM
C. M. Lisse et al 2009 ApJ 701 2019-2032
C. M. Lisse1,8, C. H. Chen2, M. C. Wyatt3, A. Morlok4,9, I. Song5, G. Bryden6 and P. Sheehan7
1 JHU-APL, 11100 Johns Hopkins Road, Laurel, MD 20723, USA
2 STScI, 3700 San Martin Drive, Baltimore, MD 21218, USA
3 Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
4 The Open University, Milton Keynes, MK7 6AA, UK
5 Department of Physics and Astronomy, The University of Georgia, Athens, GA 30602, USA
6 Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
7 Department of Physics and Astronomy, University of Rochester, Rochester, NY, USA
8 Address for correspondence: Planetary Exploration Group, Space Department, Johns Hopkins University, Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, USA.
9 Current address: CRPG-CNRS, UPR2300, 15 rue Notre Dame des Pauvres, BP20, 54501 Vandoeuvre les Nancy, France.
E-mail: email@example.com, firstname.lastname@example.org, email@example.com, A.Morlok@open.ac.uk, firstname.lastname@example.org, Geoffrey.Bryden@jpl.nasa.gov and email@example.com
ABSTRACT. The fine dust detected by infrared (IR) emission around the nearby β Pic analog star HD172555 is very peculiar. The dust mineralogy is composed primarily of highly refractory, nonequilibrium materials, with approximately three quarters of the Si atoms in silica (SiO2) species. Tektite and obsidian lab thermal emission spectra (nonequilibrium glassy silicas found in impact and magmatic systems) are required to fit the data. The best-fit model size distribution for the observed fine dust is dn/da = a –3.95±0.10. While IR photometry of the system has stayed stable since the 1983 IRAS mission, this steep a size distribution, with abundant micron-sized particles, argues for a fresh source of material within the last 0.1 Myr. The location of the dust with respect to the star is at 5.8 ± 0.6 AU (equivalent to 1.9 ± 0.2 AU from the Sun), within the terrestrial planet formation region but at the outer edge of any possible terrestrial habitability zone. The mass of fine dust is 4 × 1019-2 × 1020 kg, equivalent to a 150-200 km radius asteroid. Significant emission features centered at 4 and 8 μm due to fluorescing SiO gas are also found. Roughly 1022 kg of SiO gas, formed by vaporizing silicate rock, is also present in the system, and a separate population of very large, cool grains, massing 1021-1022 kg and equivalent to the largest sized asteroid currently found in the solar system's main asteroid belt, dominates the solid circumstellar material by mass. The makeup of the observed dust and gas, and the noted lack of a dense circumstellar gas disk, strong stellar X-ray activity, and an extended disk of β meteoroids argues that the source of the observed circumstellar materials is a giant hypervelocity (>10 km s–1) impact between large rocky planetesimals, similar to the ones which formed the Moon and which stripped the surface crustal material off of Mercury's surface.
Print publication: Issue 2 (2009 August 20)
Received 2008 November 24, accepted for publication 2009 June 16
Published 2009 August 7
Link: Abstract August 20 issue of the Astrophysical Journal
Link: Discover Magazine Blog
Link: Space.com article
Link: YouTube Video (Planetary Smash-Up)
08 August 2009
"Piloted operations at a near-Earth object (NEO)"
Rob R. Landisa, Paul A. Abellb, David J. Korsmeyera, Thomas D. Jonesc, and Daniel R. Adamod
Available online 9 June 2009.
In late 2006, NASA's Constellation Program sponsored a study to examine the feasibility of sending a piloted Orion spacecraft to a near-Earth object. NEOs are asteroids or comets that have perihelion distances less than or equal to 1.3 astronomical units, and can have orbits that cross that of the Earth. Therefore, the most suitable targets for the Orion Crew Exploration Vehicle (CEV) are those NEOs in heliocentric orbits similar to Earth's (i.e. low inclination and low eccentricity). One of the significant advantages of this type of mission is that it strengthens and validates the foundational infrastructure of the United States Space Exploration Policy and is highly complementary to NASA's planned lunar sortie and outpost missions circa 2020. A human expedition to a NEO would not only underline the broad utility of the Orion CEV and Ares launch systems, but would also be the first human expedition to an interplanetary body beyond the Earth–Moon system. These deep space operations will present unique challenges not present in lunar missions for the onboard crew, spacecraft systems, and mission control team. Executing several piloted NEO missions will enable NASA to gain crucial deep space operational experience, which will be necessary prerequisites for the eventual human missions to Mars.
Our NEO team will present and discuss the following:
• new mission trajectories and concepts;
• operational command and control considerations;
• expected science, operational, resource utilization, and impact mitigation returns; and
• continued exploration momentum and future Mars exploration benefits.
Link: ScienceDirect reference
Agenda for Upcoming "Asteroid–Comet Hazard – 2009" Conference (September 21 – 25, 2009, St. Petersburg, Russia)
Session 8. Investigations of NEOs in situ. Counteraction NEO Hazard
A. Harris (Space Science Institute).
Estimating the NEO population and impact risk: past, present and future.
M. A’Hearn (Department of Astronomy of University of Maryland).
Deep Impact and deflection of NEOs.
A. Bar-Nun, D. Laufer, I. Pat-El (Department of Geophysics and Planetary Sciences of Tel-Aviv University).
The structure of Comet Temple 1 from Deep Impact and Laboratory Experiments.
R. Landis, D. Korsmeyer (NASA Ames Research Center), P. Abell (NASA Johnson Space Center of Planetary Science Institute), D. Adamo (Trajectory Consultant), T. Jones (Association of Space Explorers).
Robotic precursors & piloted missions to near-Earth objects: a scientific and planetary defense rationale.
V. Pol’, А. Simonov (S.A. Lavochkin Scientific-Technology Association of Federal Space Agency), L. Rykhlova (Institute of Astronomy of RAS).
Reconnaissance and tracking mission to the asteroid Apophis.
V. Ivashkin, (M.V. Keldysh Institute of Applied Mathematics, RAS, Moscow, Russia, ), C. Stikhno, (S.A. Lavochkin Scientific-Technology Association, FSA, Khimki, Russia).
A study of the orbit correction of the asteroid Apophis
V. Pol’, A. Simonov (S.A. Lavochkin Scientific-Technology Association Association of Federal Space Agency).
Possibility of delivery of counteraction means to the threatening asteroids.
W. Huebner, D. Boice, S. Chocron, A. Ghosh, R. Goldstein, J. Mukherjee, W. Patrick, M. Tapley, J. Walker (Southwest Research Institute), P. Bradley, P. Giguere, J. Guzik, J. Keady, C. Plesko, K. Wohletz (Los Alamos National Laboratory), L. Johnson, (NASA Headquarters).
The engagement space for countermeasures against PHOs.
C. Maccone (International Academy of Astronautics of Italy).
Description of a NASA study to deflect hazardous asteroids.
A. Zaitsev (Non-profitable Partnership “Planetary Defense Center”), A. Koroteev, B. Liaschuk, S. Popov (K.E. Tsiolkovsky Russian Academy of Cosmonautics).
Rocket-space means of echelon of short-term reaction of the Planetary Defense System.
V. Emelyanov, Yu. Merkushev (Central Scientific-Research Institute for Mechanical Engineering).
Project parameters and efficiency of the space-based system for the warning about falls of small sized celestial bodies, moving along the collision trajectories.
N. Makhutov (A.A. Blagonravov Mechanical Engineering Research Institute of RAS), V. Puchkov (Russian Ministry for Civil Defense, Emergencies and Disaster Relief), A. Zaitsev (Non-profitable Partnership “Planetary Defense Center”).
About measures on minimization of damage from collisions with asteroids and nuclei of comets.
Z. Milan Ilitz (Serbia).
Rotational mass driver – an efficient NEO deflection concept.
V. Legostaev, V. Lopota, V. Siniyavskiy (S.P. Korolev Rocket and Space Corporation “Energia”).
On the feasibility of using nuclear power propulsion units in the program to establish Earth protection against the threat of asteroid or comet impact.
E. Kührt, S. Mottola, G. Hahn (Institute of Planetary Research of German Aerospace Center), J. Behrens, P. Spietz, S. Gerene, J. Grundmann, M. Hallmann (Institute of Space Systems of German Aerospace Center), H. Michaelis, A. Börner, K. Scheibe (Institute of Robotics and Mechatronics of German Aerospace Center).
Asteroid finder − a space-based search for IEOs.
J. Smulsky (Institute of Earth's Cryosphere of RAS), Ya. Smulsky (Institute of Thermophysics of RAS).
Evolution of the Aphophis orbit and possible use of the asteroid.
A. Zaitsev, A. Klapovsky (Non-profitable Partnership “Planetary Defense Center”).
About the approach to formation of international-legal bases of ensuring planetary defense.
Link: Program "Asteroid–Comet Hazard – 2009" Conference
Link: Conference website
07 August 2009
Upcoming Meeting of U.S. National Academies: " Review of Near-Earth Object Surveys and Hazard Mitigation Strategies" Project
Review of Near-Earth Object Surveys and Hazard Mitigation Strategies
August 10, 2009 - August 11, 2009
J. Erik Johnson Woods Hole Center
314 Quissett Ave.
Woods Hole, Massachusetts
If you would like to attend the sessions of this meeting that are open to the public or need more information please contact:
Contact Name: Rodney Howard
Phone: (202) 334-3477
Agenda:Preliminary Draft Agenda
August 10, 2009
10:00 am Meeting Convenes
5:00 pm Meeting adjourns
August 11, 2009
9:00 am Meeting convenes
5:00 pm Meeting adjourns
Link: U.S. National Academies Project Page: Review of Near-Earth Object Surveys and Hazard Mitigation Strategies
Link: August 10-11, 2009 Meeting Page
06 August 2009
From the article:
Radar imaging at NASA's Goldstone Solar System Radar on June 12 and 14, 2009, revealed that near-Earth asteroid 1994 CC is a triple system. Asteroid 1994 CC encountered Earth within 2.52 million kilometers (1.56 million miles) on June 10. Prior to the flyby, very little was known about this celestial body. 1994 CC is only the second triple system known in the near-Earth population. A team led by Marina Brozovic and Lance Benner, both scientists at NASA's Jet Propulsion Laboratory in Pasadena, Calif., made the discovery.
1994 CC consists of a central object about 700 meters (2,300 feet) in diameter that has two smaller moons revolving around it. Preliminary analysis suggests that the two small satellites are at least 50 meters (164 feet) in diameter. Radar observations at Arecibo Observatory in Puerto Rico, led by the center's director Mike Nolan, also detected all three objects, and the combined observations from Goldstone and Arecibo will be utilized by JPL scientists and their colleagues to study 1994 CC's orbital and physical properties.
The next comparable Earth flyby for asteroid 1994 CC will occur in the year 2074 when the space rock trio flies past Earth at a distance of two-and-a-half million kilometers (1.6 million miles).
OF the hundreds of near-Earth asteroids observed by radar, only about 1 percent are triple systems.
Link: JPL AsteroidWatch Article
05 August 2009
Planetary magnetic fields are created by massive molten metal currents within the planet's core. A flowing current creates a magnetic field, even when the current is massive volumes of charged liquid metal moving under the influence of temperature gradients (convection) - in fact, especially then. But magnetic analysis of Martian sites by Berkeley researchers show that the red planet's protective field was switched off half a billion years ago, and now some scientists say they know why.
John Hopkins University scientists have calculated that a period of massive asteroid impacts, known to have happened around the same time, could not only have massively impacted on the surface Deep Impact-style (with all the atmospheric alteration and great-big-crater-making that entails) but added enough energy to the planet to heat up the outer layers of the planet.
Without the huge temperature difference between the core and mantle, the mega-magnetic dynamo convection currents would be switched off - and unable to start up again when things cooled down. Remember, planetary core behavior is still carrying on from when the planets first formed - as far as they're concerned the whole "crust" thing and all life as we know it is just a cooling scum on the surface. If you break something from back then you just don't have the juice to start it up again.
Without the magnetic field Mars is defenseless against the radiation that constantly pours in from space (never mind the Fantastic Four, the only superpower cosmic rays'll give you is decomposition). Earth is thought to have survived the same space-bombing because of our superior size, with our dynamo maybe stuttering a little but - very importantly - not stopping.
"Did Mars's Magnetic Field Die With a Whimper or a Bang?"
30 April 2009
Link: ScienceNow Article
From the article...
Many moons are locked in synchronous rotation with their mother planets. Examples include the Galilean moons of Jupiter, Neptune's moon Triton and our own Moon.
In the 80s and 90s astronomers noticed that the distribution of craters on these objects was asymmetric: they were more heavily cratered on their leading hemispheres which makes sense since it seems obvious that these areas should be struck more often.
It wasn't until 2003, however, that the same asymmetric crater distribution was measured on our Moon. Now Takashi Ito at the National Astronomical Observatory in Japan and Renu Malhotra at the University of Arizona have asked an interesting question. of the data. Can the asymmetric distribution of craters on the Moon be explained by the known distribution of near Earth asteroids that are thought to have caused them? Their answer is a cautious "no".
To properly explain the crater distribution, Ito and Malhotra say some other factor must have been involved. One possibility is that we simply haven't seen all the craters yet: the ongoing lunar mapping missions may help on that score.
Another idea is that the Earth's tidal forces tear Earth-crossing asteroids apart, creating a higher number of impacts than might otherwise be expected.
But the most exciting and potentially worrying possibility is that there exists a previously unseen population of near Earth asteroids that orbit the Sun at approximately the same distance as the Earth. These have gone unnoticed because they are smaller or darker than other asteroids, say Ito and Malhotra.
"More complete observational surveys of the near-Earth asteroids can test our prediction," they say.
"Lunar Crater Stats Indicate Hidden Population of Asteroids"
03 August 2009
Link: Technology Review Article
Asymmetric impacts of near-Earth asteroids on the Moon
Authors: Takashi Ito, Renu Malhotra
(Submitted on 17 Jul 2009)
Abstract: Recent lunar crater studies have revealed an asymmetric distribution of rayed craters on the lunar surface. The asymmetry is related to the synchronous rotation of the Moon: there is a higher density of rayed craters on the leading hemisphere compared with the trailing hemisphere. Rayed craters represent generally the youngest impacts. The purpose of this paper is to test the hypotheses that (i) the population of Near-Earth asteroids (NEAs) is the source of the impactors that have made the rayed craters, and (ii) that impacts by this projectile population account quantitatively for the observed asymmetry. We carried out numerical simulations of the orbital evolution of a large number of test particles representing NEAs in order to determine directly their impact flux on the Moon. The simulations were done in two stages. In the first stage we obtained encounter statistics of NEAs on the Earth's activity sphere. In the second stage we calculated the direct impact flux of the encountering particles on the surface of the Moon; the latter calculations were confined within the activity sphere of the Earth. To represent NEAs' initial conditions, we considered two populations: one is the currently known NEAs, and the other is a synthetic population created by debiasing the orbital distribution of the known NEAs. We find that the near-Earth asteroids do have an asymmetry in their impact flux on the Moon: apex-to-antapex ratio of 1.3-1.4. However, the observed rayed crater distribution's asymmetry is significantly more pronounced: apex-to-antapex ratio of ~1.67. Our simulations suggest the existence of an undetected population of slower (low impact velocity) projectiles, such as a population of objects coorbiting with Earth.
Link: Abstract: "Asymmetric impacts of near-Earth asteroids on the Moon"
Link: Paper: Asymmetric impacts of near-Earth asteroids on the Moon [PDF]
From the article...
In 1996, astronomers identified an extraordinary object orbiting the Sun between Mars and Jupiter in the region best known for its asteroids. And yet this body, called 133P, defied description: it had the orbit of an asteroid and yet was emitting dust like a comet.
Clearly, this is a rare object. After centuries of observation, not a single other object in the asteroid belt has burped gas and dust in the same way.
So how could this have got there? According to Henry Hsieh at Queen's University, Belfast in Northern Ireland, there can be only two explanations. The first is that 133P is a comet that has somehow recently become trapped in an asteroid-like orbit. This would have required a hugely unlikely combination of gravitational kicks from other planets as the comet travelled into the solar system from the Kuiper Belt or Oort cloud.
"The Puzzle Of The Half Comet-Half Asteroid"
05 August 2009
Link: Technology Review Article
The Hawaii Trails Project: Comet-Hunting in the Main Asteroid Belt
Authors: Henry H. Hsieh (Queen's University, Belfast)
(Submitted on 31 Jul 2009)
Abstract: The mysterious solar system object 133P/(7968) Elst-Pizarro is dynamically asteroidal, yet displays recurrent comet-like dust emission. Two scenarios were hypothesized to explain this unusual behavior: (1) 133P is a classical comet from the outer solar system that has evolved onto a main-belt orbit, or (2) 133P is a dynamically ordinary main-belt asteroid on which subsurface ice has recently been exposed. If (1) is correct, the expected rarity of a dynamical transition onto an asteroidal orbit implies that 133P could be alone in the main belt. In contrast, if (2) is correct, other icy main-belt objects should exist and could also exhibit cometary activity. Believing 133P to be a dynamically ordinary, yet icy main-belt asteroid, I set out to test the primary prediction of the hypothesis: that 133P-like objects should be common and could be found by an appropriately designed observational survey. I conducted just such a survey -- the Hawaii Trails Project -- of selected main-belt asteroids in a search for objects displaying cometary activity. I made 657 observations of 599 asteroids, discovering one active object now known as 176P/LINEAR, leading to the identification of the new cometary class of main-belt comets. These results suggest that there could be ~100 currently active main-belt comets among low-inclination, kilometer-scale outer belt asteroids. Physically and statistically, main-belt comet activity is consistent with initiation by meter-sized impactors. The estimated rate of impacts and sizes of resulting active sites, however, imply that 133P-sized bodies should become significantly devolatilized over Gyr timescales, suggesting that 133P, and possibly the other MBCs as well, could be secondary, or even multigenerational, fragments from recent breakup events.
Link: Citation: The Hawaii Trails Project: Comet-Hunting in the Main Asteroid Belt
Link: Paper: The Hawaii Trails Project: Comet-Hunting in the Main Asteroid Belt [PDF]
04 August 2009
Image Credit: NASA/JPL-Caltech
Image Credit: NASA/JPL-Caltech
Image Credit: NASA/JPL-Caltech
Image Credit: NASA/JPL-Caltech
Link: JPL News Site
Link: SpaceFlightNow Article
03 August 2009
For years, [Apollo Astronaut and B612 Foundation leader Rusty] Schweickart and his colleagues at the B612 Foundation and the Association of Space Explorers have been urging the United Nations to take a more formal approach to assessing cosmic threats. Because the effects of an impact could be global, the deliberations about what to do in case an impact should have an international scope as well.
The first step is to identify potential threats: Just in the past week, Schweickart and others sent a letter urging the Australian government to restart funding for a near-Earth object search in the Southern Hemisphere. The government cut support to Spaceguard Australia in 1996, and since then asteroid-watchers have worried about the huge "blind spot" in their coverage area. (Fortunately, Australian amateur astronomers such as Anthony Wesley, who first spotted the Jupiter impact, have helped fill the gap.)
"Australia is arguably the most advanced country in the hemisphere," Philip Chapman, NASA's first Australian-born astronaut, was quoted as saying in The Australian. "Failure to contribute to the international effort is grotesquely irresponsible."
Schweickart told me in a follow-up e-mail that the jury is still out on the precise cause of the latest Jupiter impact:
"I think that the comet claim is simply a default position and perhaps a carryover from the Shoemaker-Levy 9 comet impact. Since no one saw it prior to impact, who knows whether it was a comet or asteroid. In my view, it's very much more likely to be an asteroid impact, simply due to the much higher population.
"As to why no one saw it prior to impact or knew it was going to impact… that’s pretty easy. Any asteroids that don’t come near Earth are difficult to see. The likelihood of spotting a 1-kilometer (this was probably not larger than that… most likely smaller) asteroid which circulates from the main belt out to halfway between Jupiter and Saturn is vanishingly small. The only way we’d have to know about this ahead is if it happened to be a near-Earth asteroid with an aphelion [maximum distance from the sun] greater than Jupiter's distance. That's a very small percentage of the near-Earth asteroid population.
"Still… any evidence of current impacts on any other body help to emphasize that it's only a matter of time till it's our turn. So the more the merrier!"
Link: MSNBC Cosmic Log article
From JPL Paper: D.K. Yeomans, S. Bhaskaran, S.B. Broschart, S.R. Chesley, P.W. Chodas, T. H. Sweetser, R. Schweickart, "Deflecting a Hazardous Near-Earth Object," 1st IAA Planetary Defense Conference: Protecting Earth from Asteroids, 27-30 April 2009, Granada, Spain.
Updated JPL paper (response to U.S. NRC committee and presented at the 2009 Planetary Defense Conference). From the JPL NEO website:
This short report on Near-Earth Object (NEO) hazard mitigation strategies was developed in response to a request for information by the U.S. National Research Council's Space Sciences Board on December 17, 2008 and for the Planetary Defense Conference that took place 27-30 April 2009 in Granada Spain. Although we present example simulations for specific techniques that could be employed to deflect an Earth threatening NEO, our primary goal is to discuss some of the general principles and techniques that would be germane to all NEO deflection scenarios. This report summarizes work that was carried out in early 2009 and extends an earlier, more detailed study carried out in late 2008.
Link: JPL NEO Website News Item on Updated Apophis Keyhole Analysis (PDC Paper)
Link: JPL NEO Apophis Whitepaper (April 2009)
From the JPL AsteroidWatch Widget site:
Asteroid Watch Widget
JPL's Asteroid Watch Widget tracks asteroids and comets that will make relatively close approaches to Earth. The Widget displays the date of closest approach, approximate object diameter, relative size and distance from Earth for each encounter. The object's name is displayed by hovering over its encounter date. Clicking on the encounter date will display a Web page with details about that object.
The Widget displays the next five Earth approaches to within 4.6 million miles (7.5 million kilometers or 19.5 times the distance to the moon); an object larger than about 150 meters that can approach the Earth to within this distance is termed a potentially hazardous object.
Available for Mac OS X Dashboard and Yahoo! Widgets.
Link: JPL AsteroidWatch Widget Site
02 August 2009
SGAC, Secure World Foundation (SWF) and European Space Agency (ESA) Need Help Updating ESA Planetary Database to Include NEOs
Link: SGAC Press Release
Link: SGAC official press release (PDF)
01 August 2009
Meanwhile, the impact [recent impact of an object into Jupiter] has led many to wonder about the chances that something similar might hit Earth instead. Fortunately, Jupiter is so much larger than our own planet that it acts as a gravitational attractor for cosmic debris. That makes Jupiter "our friendly big brother," Orton said.
It so happens that research newly published by the journal Science provides more data on the likelihood of killer comets - specifically, the chance that a shower of long-period comets might be pushed toward Earth.
The bad news is that computer simulations indicate such a comet shower is indeed possible. The good news is that the same simulations suggest Earth should experience a comet shower only once every 500 million years.
Long-period comets are among the wild cards in a thick deck of cosmic threats. In contrast with short-period comets, such as Comet Halley and Comet Tempel-Tuttle, long-period comets trace insanely eccentric orbits that range out beyond Neptune, Pluto and the Kuiper Belt to a little-understood region on the solar system's edge known as the Oort Cloud. The best-known example is Comet Hale-Bopp (which pays us a visit every 4,200 years).
University of Washington researchers Nathan Kaib and Thomas Quinn ran computer simulations of solar system interactions to see how long-period comets could be knocked loose from the inner Oort Cloud, a region that spans the zone between 1,000 and 20,000 AU away from the sun. (One AU, or Astronomical Unit, is equivalent to the distance between Earth and the sun - that is, 93 million miles or 150 million kilometers).
The outer Oort Cloud goes from 20,000 AU to as much as 100,000 AU, or nearly halfway out to the next star. Astronomers have long believed that comets could be jarred loose from the outer Oort Cloud by a passing star. But some of them thought the solar system was structured such that comets came only rarely from the inner Oort Cloud, in deadly bursts.
In the Science research, published online today, Kaib and Quinn report that comets from the inner Oort Cloud can indeed "penetrate Jupiter's orbit via a largely unexplored pathway" and are a "significant, if not the dominant, source" of long-period comets.
That might sound like bad news. The UW researchers see it differently, however: They say the simulations actually suggest there are fewer comets in the entire Oort Cloud, inner plus outer, than astronomers previously thought. Demystifying the inner Oort Cloud has the effect of making the whole region seem somewhat less dangerous.
"For the past 25 years, the inner Oort Cloud has been considered a mysterious, unobserved region of the solar system capable of providing bursts of bodies that occasionally wipe out life on Earth," Quinn said in a UW news release. "We have shown that comets already discovered can actually be used to estimate an upper limit on the number of bodies in this reservoir."
The simulations indicate that Jupiter and Saturn should be able to catch most of the long-period comets coming our way, like goalies catching soccer balls. Even in the worst-case scenario, only about two or three big comets would slip through and hit Earth, the researchers said.
Kaib and Quinn go so far as to suggest that the only time this happened in the past half-billion years or so was during a minor extinction event in the late Eocene geologic period, 33 million to 40 million years ago. It's thought that the late Eocene was marked by cometary impacts in present-day Chesapeake Bay and Siberia.
"If the late Eocene episode was caused by a comet shower, it was likely the most powerful shower since the Cambrian Explosion, implying that comet showers are unlikely to account for other observed extinction events," the researchers wrote.
The calculations published in Science make the specter of killer comet storms look a little less threatening. It's important to remember, however, that Kaib and Quinn are talking purely in terms of statistical analysis. The case of Jupiter's Great Black Spot illustrates that statistics can take you only so far.
Fifteen years ago, astronomers said Comet Shoemaker-Levy 9's collision with Jupiter was an exceedingly rare occurrence. Now we know that's not necessarily so. "The 1-in-a million chance of seeing one of these per century is clearly off," JPL's Orton said.
For years, JPL has been keeping track of potential cosmic threats as part of its Near-Earth Object Observation Program. Now the subject has spawned a brand-new Web site titled Asteroid Watch, which offers blog entries and a Twitter link as well as an asteroid widget. I suspect the Great Black Spot had something to do with all this.
Link: MSNBC Cosmic Log, Alan Boyle, article
"Reassessing the Source of Long-Period Comets"
Nathan A. Kaib 1* and Thomas Quinn 1
1 Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195–1580, USA.
Published Online July 30, 2009
We present numerical simulations to model the production of observable long-period comets (LPCs) from the Oort Cloud, a vast reservoir of icy bodies surrounding the Sun. We show that inner Oort Cloud objects can penetrate Jupiter's orbit via a largely unexplored dynamical pathway, and they are a significant, if not the dominant, source of known LPCs. We use this LPC production to place observationally motivated constraints on the population and mass of the inner Oort Cloud, which are consistent with giant planet formation theory. These constraints indicate that only one comet shower producing late Eocene bombardment levels has likely occurred since the Cambrian Explosion, making these phenomena an improbable cause of additional extinction events.
Link: Science Magazine article
After attending the recent 27th ISTS (International Symposium on Space Technology and Science)conference in Japan, presentations were given that elaborated upon recent Japanese thinking on NEO spacecraft missions.
The presentation was by Makoto Yoshikawa of JAXA for the paper entitled: "Hayabusa Follow-on Asteroid Sample Return Missions."
In the presentation Dr. Yoshikawa talked about the Hayabusa 2 follow on mission (following upon the very successful Japanese Hayabusa mission to asteroid Itokawa).
Dr. Yoshikawa stated that JAXA has a new proposal for Hayabusa 2, namely that they are now proposing the mission have two spacecraft with one specifically being an impactor. They would be launched on the same launch vehicle and have the same target as previous plans, 1999JU3. They would follow different trajectories after launch. The impactor mass would be 300 kg.
The implications of this change and it relation to the potential joint ESA/JAXA Macro Polo mission as well as the Don Quijote mission concept remain to be determined. All these spacecraft mission plans are dependent upon funding. But it seems the original Hayabusa 2 mission of a non-impactor sample return may have changed. This change itself is also subject to change.
Title: "Hayabusa Follow-on Asteroid Sample Return Missions"
Authors: Makoto Yoshikawa1, Hajime Yano1, Tetsuya Yamada1, Mutsuko Morimoto1, Masatoshi Matsuoka2, Junichiro Kawaguchi1, Masanao Abe1, Kazutaka Nishiyama1, Tetsuo Yoshimitsu1, Detlef Koschny3, Antonella Barucci4, David Agnolon3, Jens Romstedt3, Lutz Richter5 (1JAXA, Japan, 2NEC Aerospace Systems, Japan, 3ESTEC/ESA, The Netherlands, 4Paris Observatory, France, 5DLR, Germany)
Conference: 27th ISTS (International Symposium on Space Technology and Science), 05-12 July 2009.
Link: ISTS Website
The Minor Planet Center (MPC) operates at the Smithsonian Astrophysical Observatory (SAO), under the auspices of Division III of the International Astronomical Union (IAU), with significant funding coming from subscriptions to the various services offered by the Center.
The MPC is responsible for the designation of minor bodies in the solar system: minor planets; comets, in conjunction with the Central Bureau for Astronomical Telegrams (CBAT); and natural satellites (also in conjunction with CBAT). The MPC is also responsible for the efficient collection, computation, checking and dissemination of astrometric observations and orbits for minor planets and comets
Link: Minor Planet Center (MPC)
Link: Minor Planet Center NEO Page
A subcommittee of the panel [Review of U.S. Human Space Flight Plans Committee] studied several possibilities, including NASA’s current program to send astronauts back to the Moon by 2020, a more ambitious plan to skip the Moon and aim directly for Mars and what the members called the “flexible path,” which would avoid the “deep gravity wells” of the Moon and Mars, saving the time and cost of developing landers to carry astronauts to the surfaces of those bodies.
Edward F. Crawley, a professor at the Massachusetts Institute of Technology who headed the subcommittee, said, “The flexible path essentially goes across stepping stones” of progressively longer, more challenging missions by which NASA would learn how to operate long missions in deep space.
A flyby of the moon might be followed by more distant trips to so-called Lagrange points, first to the location where the gravity of the Moon and the Earth gravity cancel each other out, then to where the gravity of the Earth and Sun cancel out. There could also be visits to asteroids or flybys of Mars leading to landings on one or both of the low-gravity moons of Deimos and Phobo
Link: New York Times article
Link: Flexible Path Discussion at NASASpaceFlight.com
Link: Discover Magazine Blog Post on Flexible Path
Link: NASA HSF Committee "Exploration Beyond LEO" document
From the article...
A GROUP of scientists and former NASA astronauts is urging the Rudd government to join the international search for comets or asteroids on a collision course with Earth.
The call comes on the heels of this month's 40th anniversary of the Apollo 11 moon landing and the government's $160.5 million commitment to space science and astronomy, announced in the May budget.
In an open letter sent yesterday to Kevin Rudd, Julia Gillard, Science Minister Kim Carr and Defence Minister John Faulkner, the group says it's time to relaunch Spaceguard Australia, a program to survey the southern skies for potentially dangerous Near-Earth Objects like the Earthbound rock Bruce Willis destroys in the 1998 Hollywood blockbuster Armageddon.
Other signatories are David Howell, a Sydney-based international security consultant; Michael Paine, a consulting safety engineer and Australian co-ordinator for the Planetary Society in Pasadena, California; and Russell "Rusty" Schweickart, a former Apollo 9 astronaut and co-founder of the B612 Foundation, a private body dedicated to protecting Earth from NEOs.
According to the group, Australian participation in ongoing surveys -- led by NASA's Jet Propulsion Laboratory in Pasadena -- is critical.
No southern hemisphere telescopes are watching the sky. The result is a "blind spot" in coverage that could delay the identification of an NEO threat by four to 12 years, as northern and southern observations are needed to determine an object's orbit.
At present, seven NEO search programs are under way in the US, Japan and Germany.
Dr Chapman's group recommends that the commonwealth upgrade the Anglo-Australian Observatory to resurrect Australia's participation.
They also urge the government to take a leadership role, co-ordinating other southern hemisphere nations.
Until 1996 Australian astronomers participated in the global Spaceguard effort, using the Siding Spring Observatory in NSW, as well as a NASA-supported amateur instrument in Loomberah, NSW.
In 1996 the Howard government pulled funding, despite the fact that Australians had spotted roughly a third of all NEOs since the mid-1980s.
The move prompted an ultimately unsuccessful call in 2002 by more than 90 international researchers, urging then science minister Peter McGauran to reinstate funding.
"Call to reinstate asteroid search"
01 August 2009
Link: Article (the Australian)
Link: Spaceguard: Australia Facebook page with open letter
NASA's Jet Propulsion Laboratory is introducing a new Web site that will provide a centralized resource for information on near-Earth objects - those asteroids and comets that can approach Earth. The "Asteroid Watch" site also contains links for the interested public to sign up for NASA's new asteroid widget and Twitter account.
"Most people have a fascination with near-Earth objects," said Don Yeomans, manager of NASA's Near-Earth Object Program Office at JPL. "And I have to agree with them. I have studied them for over three decades and I find them to be scientifically fascinating, and a few are potentially hazardous to Earth. The goal of our Web site is to provide the public with the most up-to-date and accurate information on these intriguing objects."
The new Asteroid Watch site is online at http://www.jpl.nasa.gov/asteroidwatch .
It provides information on NASA's missions to study comets, asteroids and near-Earth objects, and also provides the basic facts and the very latest in science and research on these objects. News about near-Earth object discoveries and Earth flybys will be available and made accessible on the site via a downloadable widget and RSS feed. And for those who want to learn about their space rocks on the go, a Twitter feed is offered. "Asteroid Watch" also contains a link to JPL's more technical Near-Earth Objects Web site, where many scientists and researchers studying near-Earth objects go for information.
"This innovative new Web application gives the public an unprecedented look at what's going on in near-Earth space," said Lindley Johnson, program executive for the Near-Earth Objects Observation program at NASA Headquarters in Washington.
Link: JPL Asteroid Watch Website
Link: JPL Asteroid Watch Twitter Feed
Link: lowflyingrocks Twitter Feed
NEO News (07/30/09) Impact on Jupiter
The big news this week is the apparent impact on Jupiter that took place on July 19, 2009. This appears analogous to the 1996 impacts of Comet Shoemaker-Levy 9, except that in this case the hit was from a single projectile, probably no more than 1 km across. It has been generally called a comet in the press, although no one knows what it was made of or its orbit before hitting Jupiter. This new impact scar on Jupiter has stimulated considerable press interest in the impact threat, including some suggestions that we need to devote more resources to protecting the Earth.
The NASA NEO Program Office at JPL has inaugurated a new program to provide timely information on NEOs via Twitter and Widget. The discovery and orbit calculations for all NEOs have been available for several years at (neo.jpl.nasa.gov), but now they are adding a more user-friendly format for the general public (jpl.nasa.gov/asteroidwatch).
Coincidentally, there is also news that the U.S. Air Force will re-instate its release of information on space observations of bright fireballs, although there are no details indicating just what information will be provided or how quickly the data release will take place. This edition of NEO News is made up of various news releases and press commentary on these recent events.
NATURE NEWS: FIREBALL DATA WILL BE AVAILABLE AGAIN
Published online 8 July 2009 | Nature 460, 163 (2009) News in Brief
US Air Force will continue to share meteor data
The United States Air Force says that it will resume sharing data on incoming meteors with astronomers. The Air Force collects the data with a network of satellites and sensors designed as a missile early warning system. For more than a decade, it provided them to astronomers on an ad-hoc basis, but the informal relationship came to a halt earlier this year (see Nature 459, 896-897; 2009). Astronomers feared that the Air Force had put a stop to the practice, but "the data will still flow", says Andy Roake, a spokesman for Air Force Space Command in Colorado Springs, Colorado. The Air Force is developing procedures for releasing data that will be faster, more systematic and in compliance with classification procedures. Data sharing could resume within the next few months.
NEW NASA IMAGES INDICATE OBJECT HITS JUPITER
Jet Propulsion Laboratory, Pasadena, Calif. July 20, 2009
Scientists have found evidence that another object has bombarded Jupiter, exactly 15 years after the first impacts by the comet Shoemaker-Levy 9. Following up on a tip by an amateur astronomer that a new dark "scar" had suddenly appeared on Jupiter, this morning between 3 and 9 a.m. PDT (6 a.m. and noon EDT) scientists at NASA's Jet Propulsion Laboratory in Pasadena, Calif., using NASA's Infrared Telescope Facility at the summit of Mauna Kea, Hawaii, gathered evidence indicating an impact.
New infrared images show the likely impact point was near the south polar region, with a visibly dark "scar" and bright upwelling particles in the upper atmosphere detected in near-infrared wavelengths, and a warming of the upper troposphere with possible extra emission from ammonia gas detected at mid-infrared wavelengths
"We were extremely lucky to be seeing Jupiter at exactly the right time, the right hour, the right side of Jupiter to witness the event. We couldn't have planned it better," said Glenn Orton, a scientist at JPL.
The new Jupiter images are online at: http://www.jpl.nasa.gov/news/news.cfm?release=2009-112 .
Orton and his team of astronomers kicked into gear early in the morning and haven't stopped tracking the planet. They are downloading data now and are working to get additional observing time on this and other telescopes.
This image was taken at 1.65 microns, a wavelength sensitive to sunlight reflected from high in Jupiter's atmosphere, and it shows both the bright center of the scar (bottom left) and the debris to its northwest (upper left). "It could be the impact of a comet, but we don't know for sure yet," said Orton. "It's been a whirlwind of a day, and this on the anniversary of the Shoemaker-Levy 9 and Apollo anniversaries is amazing." Shoemaker-Levy 9 was a comet that had been seen to break into many pieces before the pieces hit Jupiter in 1994.
Leigh Fletcher, a NASA postdoctoral student at JPL who worked with Orton during these latest observations said, "Given the rarity of these events, it's extremely exciting to be involved in these observations. These are the most exciting observations I've seen in my five years of observing the outer planets!"
The observations were made possible in large measure by the extraordinary efforts of the Infrared Telescope Facility staff, including telescope operator William Golisch, who adroitly moved three instruments in and out of the field during the short time the scar was visible on the planet, providing the wide wavelength coverage.
JUPITER'S BEEN HIT!
By Richard A. Kerr, Science NOW Daily News, 20 July 2009
A large object has slammed into Jupiter, leaving behind a giant black smudge that was first reported yesterday by an amateur astronomer. The find is only the second time in recorded history that scientists have glimpsed an impact scar in the atmosphere of a giant planet. "I never expected I'd get to see something like this," says astronomer Leigh Fletcher, a postdoc at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California.
Amateur astronomer Anthony Wesley had been taking routine images of Jupiter through his 37-centimeter telescope (pros would be on a 1000-centimeter instrument) in Murrumbateman, Australia, at about 11:30 p.m. local time, when he noticed something unusual: a dark spot several thousands of kilometers across rotating into view high in Jupiter's south polar region (see picture). Wesley had been about to end his observing run, and he initially considered passing the spot off as a typical dark polar storm. But he decided to keep at it, and in 15 minutes more he believed he was seeing something else entirely.
Wesley suspected an impact and soon contacted Fletcher and JPL astronomer Glenn Orton. As luck would have it, the duo had previously scheduled time on the NASA Infrared Telescope on Hawaii (remotely operated from JPL), so they took a closer look. They found the same distinctive infrared signature as Orton and others saw 15 years ago this week when the 21-plus fragments of disrupted comet Shoemaker-Levy 9 slammed into Jupiter one after the other (Science, 29 July 1994, p. 601). "We've been incredibly fortunate to have a talented amateur report this within hours," says Fletcher. Such amateurs "are doing some of the fundamental work of observing what's happening on Jupiter," adds Orton.
The impact "was a bit of a surprise," says astronomer Heidi Hammel of the Space Science Institute in Boulder, Colorado, who observed the 1994 impacts with the Hubble Space Telescope. "We all thought these were a little more rare." This one--a solitary event so far--looks like one of Shoemaker-Levy 9's medium-size impacts, says Hammel. How large the rocky asteroid or icy comet was is hard to estimate, says astronomer Harold Weaver of the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. There was never any consensus on the size of the Shoemaker-Levy 9 objects, but this one might have been several hundred meters across--a kilometer at most--and traveling at tens of thousands of kilometers per hour.
If scientists are to retrieve any new information about jovian impacts, they'll have to be quick about it. Winds are tearing the black splotch apart even as astronomers race to submit their emergency proposals for telescope time--including time on the recently renovated Hubble Space Telescope.
JUPITER GETS A BLACK EYE
The Wall Street Journal, July 24, 2009, By Michio Kaku
We sometimes forget that the universe is a violent place. This week, astronomers in Hawaii recorded an exceedingly rare event. An amazing photograph revealed a comet or asteroid, probably no more than a mile across, plowing into Jupiter's atmosphere. The impact created a fireball roughly the size of the planet earth.
The good news is that Jupiter was just doing its job, cleaning out the solar system of stray comets and asteroids. Jupiter, 318 times more massive than the earth, acts like a cosmic vacuum cleaner, sucking in or deflecting debris left over from the solar system's birth 4.5 billion years ago. If it weren't for Jupiter's colossal gravitational field, we wouldn't be here, since the Earth would be hit with deadly comet and meteor impacts every month or so. Most of the U.S. would just be an empty graveyard of bleak craters.
The bad news is that a comet impact could happen to us. A black eye for Jupiter would be a body blow to the earth. We got a taste of this back in 1908, when something the size of an apartment building plowed into Tunguska, Siberia. This "city-buster" flattened 100 million trees with the force of a hydrogen bomb. But this recent Jupiter comet, much larger and coming in at perhaps 100,000 miles per hour, would have unleashed the power of hundreds of H-bombs. It might have engulfed most of the East Coast in a huge firestorm, triggering a massive tsunami and destabilizing the weather.
According to Hollywood, we can always send our astronauts on a space shuttle to intercept a comet and blow it up with H-bombs. Wrong. Blowing up a comet with nuclear bombs creates chunks of debris, increasing the area of destruction. So we are sitting ducks to a potential impact from deep space.
So what's the lesson from all of this? Maybe Mother Nature has a sense of humor. An impact like the recent one in Jupiter happened 15 years ago, in late July, after the Shoemaker-Levy 9 comet broke up into 20 pieces, each of which plunged into Jupiter, creating a dazzling display of cosmic fireworks. Scientists used to believe that these collisions took place once every few thousand years, not 15 years. So perhaps Mother Nature was just trying to show what little scientists really understand about these cosmic collisions.
But it also happened on the 40th anniversary of the Moon landing. So maybe Mother Nature was reminding us that the universe is, after all, a violent place-that we may one day need a new home. The Earth lies in the middle of a cosmic shooting gallery. The proof comes out every night when we gaze at the Moon. When viewing the film of Neil Armstrong and Buzz Aldrin bobbing among the barren craters of the Moon, we are reminded that each crater was gouged out by a titanic impact.
In addition, there are more than 5,000 so-called near-Earth objects, carefully tracked by telescope, that can cross near the orbit of the earth. One of them, the asteroid Apophis, is about the size of the Rose Bowl. It will graze the Earth in 2029 and again in 2036, passing below some of our satellites.
But there are also many unnamed comets outside the solar system whose orbits are totally unknown and unpredictable. They would give us little warning and catch us totally off-guard, like the comet that just hit Jupiter.
So in the long term, perhaps we should look at the space program as an insurance policy. Not only has the space program given us a bonanza of benefits (such as weather satellites, the Global Positioning System, telecommunications, etc.), it also provides a gateway to the stars. Over the course of the next few centuries, maybe we should use that gateway to plan to be a "two planet species." Life is too precious to place in one basket.
In August, President Barack Obama will receive a major report from the U.S. human space flight plans committee about the future of space travel, which could be a turning point for NASA in the 21st century. He should remember the Jupiter hit as he considers the report.
-Mr. Kaku is the author of "Physics of the Impossible: a Scientific Exploration into the World of Phasers, Force Fields, Teleportation, and Time Travel" (Doubleday, 2008).
JUPITER: OUR COSMIC PROTECTOR?
By Dennis Overbye, New York Times, July 25, 2009
Jupiter took a bullet for us last weekend. An object, probably a comet that nobody saw coming, plowed into the giant planet's colorful cloud tops sometime Sunday, splashing up debris and leaving a black eye the size of the Pacific Ocean. This was the second time in 15 years that this had happened. The whole world was watching when Comet Shoemaker-Levy 9 fell apart and its pieces crashed into Jupiter in 1994, leaving Earth-size marks that persisted up to a year.
That's Jupiter doing its cosmic job, astronomers like to say. Better it than us. Part of what makes the Earth such a nice place to live, the story goes, is that Jupiter's overbearing gravity acts as a gravitational shield deflecting incoming space junk, mainly comets, away from the inner solar system where it could do for us what an asteroid apparently did for the dinosaurs 65 million years ago. Indeed, astronomers look for similar configurations - a giant outer planet with room for smaller planets in closer to the home stars - in other planetary systems as an indication of their hospitableness to life.
Anthony Wesley, the Australian amateur astronomer who first noticed the mark on Jupiter and sounded the alarm on Sunday, paid homage to that notion when he told The Sydney Morning Herald, "If anything like that had hit the Earth it would have been curtains for us, so we can feel very happy that Jupiter is doing its vacuum-cleaner job and hoovering up all these large pieces before they come for us."
But is this warm and fuzzy image of the King of Planets as father-protector really true? "I really question this idea," said Brian G. Marsden of the Harvard-Smithsonian Center for Astrophysics, referring to Jupiter as our guardian planet. As the former director of the International Astronomical Union's Central Bureau for Astronomical Telegrams, he has spent his career keeping track of wayward objects, particularly comets, in the solar system. Jupiter is just as much a menace as a savior, he said. The big planet throws a lot of comets out of the solar system, but it also throws them in.
Take, for example, Comet Lexell, named after the Swedish astronomer Anders Lexell. In 1770 it whizzed only a million miles from the Earth, missing us by a cosmic whisker, Dr. Marsden said. That comet had come streaking in from the outer solar system three years earlier and passed close to Jupiter, which diverted it into a new orbit and straight toward Earth. The comet made two passes around the Sun and in 1779 again passed very close to Jupiter, which then threw it back out of the solar system.
"It was as if Jupiter aimed at us and missed," said Dr. Marsden, who complained that the comet would never have come anywhere near the Earth if Jupiter hadn't thrown it at us in the first place.
Hal Levison, an astronomer at the Southwest Research Institute, in Boulder, Colo., who studies the evolution of the solar system, said that whether Jupiter was menace or protector depended on where the comets came from. Lexell, like Shoemaker Levy 9 and probably the truck that just hit Jupiter, most likely came from an icy zone of debris known as the Kuiper Belt, which lies just outside the orbit of Neptune, he explained. Jupiter probably does increase our exposure to those comets, he said.
But Jupiter helps protect us, he said, from an even more dangerous band of comets coming from the so-called Oort Cloud, a vast spherical deep-freeze surrounding the solar system as far as a light-year from the Sun. Every once in a while, in response to gravitational nudges from a passing star or gas cloud, a comet is unleashed from storage and comes crashing inward.
Jupiter's benign influence here comes in two forms. The cloud was initially populated in the early days of the solar system by the gravity of Uranus and Neptune sweeping up debris and flinging it outward, but Jupiter and Saturn are so strong, Dr. Levison said, that, first of all, they threw a lot of the junk out of the solar system altogether, lessening the size of this cosmic arsenal. Second, Jupiter deflects some of the comets that get dislodged and fall back in, Dr. Levison said. "It's a double anti-whammy," he said.
Asteroids pose the greatest danger of all to Earth, however, astronomers say, and here Jupiter's influence is hardly assuring. Mostly asteroids live peacefully in the asteroid belt between Mars and Jupiter, whose gravity, so the standard story goes, keeps them too stirred to coalesce into a planet but can cause them to collide and rebound in the direction of Earth.
That's what happened, Greg Laughlin of the University of California at Santa Cruz, said, to a chunk of iron and nickel about 50 yards across roughly 10 million to 100 million years ago. The result is a hole in the desert almost a mile wide and 500 feet deep in northern Arizona, called Barringer Crater. A gift, perhaps, from our friend and lord, Jupiter. [Note from DM: The accepted age of Meteor [Barringer] Crater is 50,000 years, orders of magnitude less than 10-100 million years.]
COULD EARTH BE HIT, LIKE JUPITER JUST WAS?
Charles Q. Choi, space.com - Jul 28, 2009
The recent bruising Jupiter received from a cosmic impact is a violent reminder that our solar system is a shooting gallery that sometimes blasts Earth. Still, what are the odds of a cosmic impact threatening our planet?
So far 784 near-Earth objects (NEOs) more than a half-mile wide (1 km) have been found. "If an object of about the same size that just hit Jupiter also hit Earth - it was probably a typical cometary object of a kilometer or so in size (0.6 miles) - it would have been fairly catastrophic," explained astronomer Donald Yeomans, manager of NASA's Near-Earth Object program office at the Jet Propulsion Laboratory in Pasadena, Calif.
Scientists have ruled out the chances of an Earth impact for all of these 784 large NEOs. Still, lesser objects also pose a risk, and researchers estimate more than 100 large NEOs remain to be found.
Billions of years ago, impacts were far more common. Our Moon retains a record of the pummeling it and Earth took: the Moon's craters remain, while on Earth, most scars of ancient impacts have been folded back into the planet or weathered away.
Today's solar system is far less crowded, and in fact Jupiter, having more mass and gravity, scoops up a lot of the dangerous objects, as does the sun. Currently just one NEO of all the objects scientists are tracking poses any significant chance of hitting the Earth - 2007 VK184. If this roughly 425-foot-wide (130 meters) asteroid hit our planet, it would strike with an energy of roughly 150 million tons of TNT, or more than 10,000 times that of the atom bomb dropped on Hiroshima.
Roughly 100 telescopic observations made so far suggest that 2007 VK184 has a 1-in-2,940 chance of hitting Earth 40 to 50 years from now. However, if the past is any guide, further observations to refine computations of its orbit very likely will downgrade its probability of hitting Earth to virtually nothing, Yeomans said.
Of remaining concern are the NEOs that we do not see. Researchers suspect about 156 large NEOs 1 kilometer in diameter or larger remain to be found, and when it comes to dangerous NEOs in general, "when we get down to 140 meters (460 feet) or larger diameter objects, we think we've discovered about 15 percent of them, and with 50 meters (164 feet) or larger diameter, we've discovered less than 5 percent of them," Yeomans explained.
On average, an NEO roughly a half-mile wide or larger hits the Earth roughly every 500,000 years, "so we're not expecting one anytime soon," Yeomans explained. "For 500 meters (1,640 feet), we're talking a mean interval of about 100,000 years," he added. "When you get down to 50 meters, the mean interval is about 700 years, and for 30 meters (98 feet), about 140 years or so, but by then you're getting down to a size where you won't expect any ground damage, as they burn up in the atmosphere at about 25 meters (82 feet) in diameter and smaller, probably for an impressive fireball event."
When it comes to truly monstrous NEOs some 10 kilometers (6.2 miles) or larger, of the size thought to have helped kill off the dinosaurs, "that's a 100 million year event, and in fact, I don't think there is anything like that we see right now," Yeomans said. "The largest near-Earth object that can actually cross the Earth's path, Sisyphus, has a diameter of 8 kilometers (5 miles), and the largest that is termed a potential hazard is Toutatis, which has a diameter of approximately 5.4 km (3.35 miles)."
Keeping watch; There are currently four teams worldwide actively looking for both large and small NEOs, Yeomans said. "We're concentrating on the large ones for now, but hopefully with the next generation of search, we'll be more efficient in finding the smaller objects, to find 90 percent of the total population of potential hazards larger than 140 meters," he added.
Keeping an eye on NEOs might not just be healthy for humanity, but also help lead us out into space. "They're easy objectives to get to, and asteroids have significant metal resources that can be mined, while comets have significant water resources for space habitats or travel," Yeomans said. "If you want to build a habitat in space, you're not going to build it all on the ground and launch it up, since that's too expensive - you want to go up and look for resources instead."
Furthermore, asteroids and comets are among the objects that have changed the least since the birth of the solar system roughly 4.6 billion years ago, and might reveal vital clues behind the mysterious process. "They may well have delivered the water and carbon-based molecules to Earth that allowed life to form, so they're extremely important for study in that direction," Yeomans added.
WEB UPDATES ON NEOS FROM NASA
Jet Propulsion Laboratory, Pasadena, Calif.
Internet Advisory: 2009-115. July 29, 2009
NASA to Provide Web Updates on Objects Approaching Earth
PASADENA, Calif. -- NASA's Jet Propulsion Laboratory is introducing a new Web site that will provide a centralized resource for information on near-Earth objects - those asteroids and comets that can approach Earth. The "Asteroid Watch" site also contains links for the interested public to sign up for NASA's new asteroid widget and Twitter account.
"Most people have a fascination with near-Earth objects," said Don Yeomans, manager of NASA's Near-Earth Object Program Office at JPL. "And I have to agree with them. I have studied them for over three decades and I find them to be scientifically fascinating, and a few are potentially hazardous to Earth. The goal of our Web site is to provide the public with the most up-to-date and accurate information on these intriguing objects."
The new Asteroid Watch site is online at http://www.jpl.nasa.gov/asteroidwatch. It provides information on NASA's missions to study comets, asteroids and near-Earth objects, and also provides the basic facts and the very latest in science and research on these objects. News about near-Earth object discoveries and Earth flybys will be available and made accessible on the site via a downloadable widget and RSS feed. And for those who want to learn about their space rocks on the go, a Twitter feed is o ffered. "Asteroid Watch" also contains a link to JPL's more technical Near-Earth Objects Web site, where many scientists and researchers studying near-Earth objects go for information.
"This innovative new Web application gives the public an unprecedented look at what's going on in near-Earth space," said Lindley Johnson, program executive for the Near-Earth Objects Observation program at NASA Headquarters in Washington. NASA supports surveys that detect and track asteroids and comets passing close to Earth. The Near-Earth Object Observation Program, commonly called "Spaceguard," also plots the orbits of these objects to determine if any could be potentially hazardous to our planet.
PLANETARY SOCIETY POLL OF MEMBERS
July 29, 2009
The results of our 2009 Member Survey tell us loud and clear that the number-one supported Planetary Society program-with nearly 90 percent of Society members strongly behind it-is "Monitoring potentially dangerous near-Earth asteroids and comets."
We couldn't agree more. An asteroid or comet impact may be a rare event, but when one happens, all life on Earth could be affected. Just ask the dinosaurs...
So we're asking you to help support the Society's three-part initiative to address this important threat:
1. Gene Shoemaker NEO Grants: This program offers small, but crucial, financial awards to amateur and under-funded professional observers who are making substantial contributions to vital near-Earth object research.
2. Apophis Mission Design Competition: Last year's successful competition designed ways to tag and track this asteroid. The next step might be to design a mission to send human investigators to explore and characterize a threatening object, such as Apophis.
3. Advocacy Action: As the largest grassroots space organization, we must mobilize public support and leverage our partnerships in the astronomical community to force action now.
Protecting our planet from a catastrophic hit is not a problem that can wait until tomorrow. It's not an exaggeration to say that an incoming asteroid or comet could devastate our civilization. It's the only preventable natural disaster and we need to act now to prepare our defenses.
NEO News (now in its fifteenth year of distribution) is an informal compilation of news and opinion dealing with Near Earth Objects (NEOs) and their impacts. These opinions are the responsibility of the individual authors and do not represent the positions of NASA, Ames Research Center, the International Astronomical Union, or any other organization. To subscribe (or unsubscribe) contact firstname.lastname@example.org. For additional information, please see the website http://impact.arc.nasa.gov. If anyone wishes to copy or redistribute original material from these notes, fully or in part, please include this disclaimer.