Videos from Mars

From OnOrbit...

A new Mars movie clip gives us a rover's-eye view of a bluish Martian sunset, while another clip shows the silhouette of the moon Phobos passing in front of the sun. America's Mars Exploration Rover Opportunity, carefully guided by researchers with an artistic sense, has recorded images used in the simulated movies.





Link: OnOrbit Article

Link: YouTube Video ("Mars Moon Phobos Eclipse")

Link: YouTube Video ("I'm Dreaming of a Blue Sunset--on Mars")

Article: "Solar Sail Flotilla Could Divert Possibly Dangerous Asteroid"

An illustration of how solar sails might help deflect the asteroid Apophis. Credit: Olivier Boisard

Selections from the article...

A flotilla of solar sail spacecraft could change the course of the asteroid Apophis — which is headed a little too close to Earth for comfort — by shading the space rock from solar radiation, according to a French researcher.

Such a plan could help shift Apophis into a slightly safer orbit by the time it is expected to swing by Earth on April 13, 2036. But experts have warned previously that any efforts to divert the space rock could actually make matters worse.

The preliminary concept idea was proposed at a symposium on solar sails – which are spacecraft powered by sunlight pushing against a sail – a few months ago at the New York City College of Technology in Brooklyn.

"Apophis is a nice target for launching this kind of mission for 20 years from now; not too far, not too close," said Jean-Yves Prado, an engineer at the National Center for Space Study (CNES) in France.

A group of formation-flying solar sails could alter the asteroid's course by eliminating the so-called Yarkovsky effect, a phenomenon described by Russian engineer I.O. Yarkovsky a century ago.

That effect occurs when the sun warms an asteroid more on the sun-facing side than the far side. The rock then emits more thermal radiation on its near side, which creates a bit of thrust and changes its momentum slightly.

"It's really a very small effect and doesn't apply to very small asteroids because the temperature would be quite negligible, so thrust is negligible," Prado explained. "It also does not apply to very large asteroids because they are too heavy."

But for Apophis, which falls just in the middle of that mass range, the effect could make a difference.

The proposed mission would deploy four 441-pound (200 kg) solar sails from a transfer module that used solar electric propulsion to reach Apophis. Previous spacecraft that have used solar electric propulsion include NASA's Deep Space 1 and Dawn probes.

Once deployed, the solar sails would hover a few kilometers above the space rock and fly in formation according to master control by the transfer module, without a direct link between Earth and the individual sails.

The module could also position itself as a small gravity tractor to provide a small gravitational push on Apophis, Prado suggested.

A previous NASA assessment of possible asteroid deflection methods had placed solar sails relatively high in terms of readily available and not-too-complex technology.

Launch windows would become available for such a mission to launch aboard a Russian Soyuz-Fregat rocket in 2016 and 2019, Prado said. He added that a second redundant mission could also launch to ensure success.

Several other solar sail researchers at the symposium raised questions about the mission design. One questioned the need for a chemical propulsion system on each solar sail that would balance out the solar pressure and keep the sails flying in their proper place.

Prado replied that his group had examined the possibility of using solar electric propulsion to also maintain low thrust and keep the solar sails in place, but had ruled it out based on cost.

Another researcher suggested that simply crashing four spacecraft with the mass of the solar sails into Apophis might be simpler.

An earlier, unrelated Russian proposal to nudge the space rock aside has been met with skepticism, in part because any solution might worsen Earth's chances, given the uncertainty regarding Apophis' exact trajectory.

NASA scientists previously pegged the possibility of an Apophis collision with Earth at a low 1-in-250,000 chance in 2036, when Apophis is expected to approach within 18,300 miles (29,450 km) of the planet in 2036.

The asteroid's second near pass by Earth comes in 2068, when it has a three-in-a-million chance (or about 1-in-333,000) of impacting on the planet.

Link: Article

Article: "Experts Push for a NASA Asteroid-Hunting Spacecraft"

A Near-Earth Object Survey spacecraft planned by Ball Aerospace & Technologies Corporation. Placed in a Venus-like orbit, its mission would be to on the prowl for space rocks near Earth. Credit: Ball Aerospace

Selections from the article...

One concept that has already been fleshed out is dubbed the NEO Survey mission, a detailed appraisal done by Ball Aerospace & Technologies Corporation in Boulder, Colo.

Results of a study by Ball Aerospace highlighted how best to meet the George E. Brown objectives for detecting NEOs.

As explained in a Ball Aerospace white paper review provided to SPACE.com, in only 1.6 years, a spacecraft could locate all of the roughly 165 feet (50 meter) diameter, and larger, nearby space rocks that are potentially accessible for human spaceflight, and within 7.5 years could catalogue 90 percent of all NEOs greater than 459 feet (140 meters) in diameter.

"We have more work to do, but what we've created is a very high-quality existence proof. We have a point design based on real engineering with real parts," said Robert Arentz, a Ball Aerospace Advanced Systems Manager.

Arentz told SPACE.com that the NEO survey spacecraft draws upon the firm's heritage of working on NASA's space-based observatories – from the Hubble Space Telescope and the Kepler exo-planet hunter to the Spitzer infrared telescope and the Wide-field Infrared Survey Explorer, along with the company's comet-smacking Deep Impact spacecraft.

The internally funded Ball Aerospace concept has not yet been given a green light by NASA, noted Kevin Miller, a Ball Advanced Systems Manager, but the point design does showcase proven capabilities and an affordable approach, he said. The work uses a recipe "to establish confidence that, yes, this really is a very tractable problem," Miller said.

In order to meet the George E. Brown requirements to find 90 percent of all NEOs larger than some 460 feet (140 meters) within 7 years, the NEO Survey mission would cost roughly $638 million. The catalog it would yield is a superset of the targets that NASA human spaceflight planners would find of interest for piloted excursions to selected space rocks.

Given a go, the NEO hunter from start to launch should take around 42 months to develop, Arentz added.

But there are technological challenges in building the NEO survey spacecraft.

Dealing with solar radiation is one. The heat load from a location so near the sun means the spacecraft would need a large thermal shield and cryocooler hardware. Also, the telescope's photon-gathering array requires highly advanced engineering.

The key is to prevent the intense solar radiation at Venus from reaching the telescope. This is done by careful design of the spacecraft's solar array and use of two thermal shields between the main array and the telescope.

The spacecraft design, Arentz said, is based largely on the Kepler planet-hunting spacecraft design to reduce cost and risk.

And, if two NEO-hunting spacecraft were placed in roughly opposite locales in a Venus-like orbit, this would allow a binocular view of space rocks, and scientists could chart them with an even greater degree of tracking accuracy.

Link: Article ("Experts Push for a NASA Asteroid-Hunting Spacecraft")

Paper: "Moving an asteroid with electric solar wind sail"

Sini Sanvia Merikallio has an updated paper based upon her winning entry for the SGAC 2009 Move An Asteroid technical paper competition. Related to the technology discussed in the paper, there is a European Union (EU) project working on the electric solar wind concept that will have a kickoff meeting this week. Paper highlights follow...

Moving an asteroid with electric solar wind sail

S. Merikallio and P. Janhunen
Finnish Meteorological Institute, Po. Box. 503, FIN-00101, Helsinki, Finland

Astrophys. Space Sci. Trans., 6, 41-48, 2010
www.astrophys-space-sci-trans.net/6/41/2010/
doi:10.5194/astra-6-41-2010
© Author(s) 2010. This work is distributed under the Creative Commons Attribution 3.0 License.

Abstract. The electric solar wind sail (E-Sail) is a new propulsion method for interplanetary travel which was invented in 2006 and is currently under development. The E-Sail uses charged tethers to extract momentum from the solar wind particles to obtain propulsive thrust. According to current estimates, the E-Sail is 2-3 orders of magnitude better than traditional propulsion methods (chemical rockets and ion engines) in terms of produced lifetime-integrated impulse per propulsion system mass. Here we analyze the problem of using the E-Sail for directly deflecting an Earth-threatening asteroid. The problem then culminates into how to attach the E-Sail device to the asteroid. We assess alternative attachment strategies, namely straightforward direct towing with a cable and the gravity tractor method which works for a wider variety of situations. We also consider possible techniques to scale up the E-Sail force beyond the baseline one Newton level to deal with more imminent or larger asteroid or cometary threats. As a baseline case we consider an asteroid of effective diameter of 140 m and mass of 3 million tons, which can be deflected with a baseline 1 N E-Sail within 10 years. With a 5 N E-Sail the deflection could be achieved in 5 years. Once developed, the E-Sail would appear to provide a safe and reasonably low-cost way of deflecting dangerous asteroids and other heavenly bodies in cases where the collision threat becomes known several years in advance.

Link: Full Article (PDF, 7229 KB)

Link: Supplement (3828 KB)

Link: Paper Reference

Article on ATLAS (for the Asteroid Terrestrial-impact Last Alert System)

Selections from the space.com article on ATLAS (for the Asteroid Terrestrial-impact Last Alert System)...

An early warning system that could give Earth a week's notice or more before a space rock destroyed a city would cost only $1 million per observatory, its leading proponent suggests.

Given current technologies, this lead time would not be enough to mount a mission to deflect the incoming object, but it could be enough to evacuate the area under threat.

Astronomer John Tonry at the University of Hawaii mentioned a near-miss in 2009 as he stressed the need for an early warning system against cosmic impacts.

According to estimates by Tonry and other researchers, the rate of impact by asteroids at least 460 feet (140 meters) long is just once per 20,000 years or more — but the smaller the rock, the larger the risk. A roughly 160-foot-long (50 meters) object like the one that devastated the Tunguska area in Russia in 1908 is likely to impact Earth about once every millennium, while a 65- to 100-foot-long asteroid (20 to 30 meters) should strike once every century.

The National Research Council estimated a 160-foot-long object would cause an average of 30,000 deaths.

Tonry details his analysis in a paper set to appear in the January issue of the Publications of the Astronomical Society of the Pacific.

The network the researchers propose, dubbed ATLAS (for the Asteroid Terrestrial-impact Last Alert System), would consist of two observatories roughly 60 miles (100 km) apart that together would scan the visible sky twice a night. Each observatory would house four relatively small telescopes some 10 inches (25 cm) in aperture, as well as a camera for each telescope. The distance between the observatories would provide a way of separating nearby and distant moving objects, and the system would be able to help pinpoint the location and time of an impact to a few miles and a few seconds.

Each telescope and each camera would cost roughly $50,000. The software would take up the lion's share of expenses, bringing the cost for each observatory to $1 million. Tonry also projected $500,000 annually for staff, maintenance and other operating costs. He and his colleagues have submitted a $3 million proposal to NASA to build two observatories and operate them for two years.

ATLAS could provide three weeks' warning for 460-foot-long objects and one week's notice for 160-foot-long impactors. The smaller the object, the less warning there would be; a 65- to 100-foot-long asteroid might draw two or three days warning, while 33-foot-long objects might get one.

As currently proposed, ATLAS would detect more than half the impactors longer than 160 feet, and nearly two-thirds of those 460 feet long. The chances of detection go up with more telescopes, Tonry said, which would allow ATLAS to compensate for cloudy weather or lack of coverage in the Southern Hemisphere. Still, ATLAS' detection rate would never go higher than roughly 75 percent, since it could spot objects coming from the blinding direction of the sun.

Link: Article

Link: ATLAS website

Misc. Videos on Asteroid Discoveries

>
YouTube Video ("Asteroid Discovery From 1980 - 2010 (w/Credits)")


YouTube Video ("Asteroid Discovery From 1980 - 2010")

Article: "Rutgers scientists: Asteroids did kill the dinosaurs"

Credit: Nick Romanenko, Rutgers University. Research scientist Paul Field, professors Ken Miller and Rob Sherrell with one of the core samples from Tighe Park, Freehold, N.J.

Selections from the article...

Sometimes, you just can’t trust the iridium. A silvery-white natural metal that’s a member of the platinum family, iridium is a key ingredient in the manufacture of spark plugs. Iridium is also an important piece of evidence in a mystery that scientists have debated for decades – why did dinosaurs disappear from the face of the earth?

The prevailing scientific consensus is that at least one asteroid – possibly more – hit the earth about 65 million years ago, showering the planet with dust and debris, blocking sunlight, causing firestorms, and marking the end of the Cretaceous Period and the beginning of the Paleogene Period. Most scientists believe the impact was directly responsible for the mass extinction of many species of plants and animals – most famously, the dinosaurs.

The impact also left a clue – a chemical signature in the earth’s crust called the “iridium anomaly.” Iridium is rare in the earth’s crust but far more abundant in asteroids. That’s why, all over the world, scientists find unusually high concentrations of iridium in sediment layers at the boundary between the Cretaceous and Paleogene periods – called the K-Pg Boundary by geologists.

All over the world, that is, except in Freehold, New Jersey – 25 miles down the highway from Rutgers University’s New Brunswick Campus.

In several cores drilled at sites around New Jersey – much of which was covered by the ocean when dinosaurs roamed the earth – fossilized sea creatures are found below the K-Pg Boundary, buried by debris that contains iridium. This evidence supports the iridium anomaly – and the consensus that asteroids killed the dinosaurs..

But not in Freehold. In 2007, scientists Neil H. Landman, of the American Museum of Natural History, and Ralph O. Johnson found fossils above the iridium-laden boundary in Freehold’s Tigh Park. Johnston is a self-educated paleontologist from West Long Branch, N.J.

Some scientists argue that the work of Landman and Johnson casts doubt on the asteroid consensus. These scientists say the Freehold evidence suggests dinosaur extinction was caused by catastrophic volcanic eruptions.

Enter Rutgers geologist Ken Miller, a professor of earth and planetary science in the School of Arts and Sciences. According to a paper authored by Miller, Rob Sherrell, Paul Field. and their colleagues in the journal Geology, the real explanation for the Freehold findings is far more simple: The iridium moved.

And how do they know that? Sherrell and Field, of the Institute of Marine and Coastal Sciences in the School of Environmental and Biological Sciences, went through a highly specialized, painstaking process of geochemical analysis to pinpoint the location of the K-Pg barrier at another Freehold site near the one excavated by Landman and Johnson.

Link: Article (Rutgers scientists: Asteroids did kill the dinosaurs)

1958 Italian Asteroid movie (The Day the Sky Exploded)

Mexican Lobby Card for "The Day the Sky Exploded"

The Day The Sky Exploded (1958)


The Day The Sky Exploded (Part 1/9)

Article on the Space Review (from Dwayne Day) on a 1958 Italian Asteroid movie (The Day the Sky Exploded)...

If you turn on the Discovery Science Channel on a lazy Saturday afternoon, there is a pretty good chance that they will be showing a “documentary” about killer asteroids. That word should always be used in quotation marks, because many of these shows contain some ridiculous errors. There are easily several dozen of these shows, some of them dating back to the mid-1990s. But if you try to get away by switching to the SyFy Channel, there is a pretty good chance that—if you don’t get stuck with Megashark vs. Giant Octopus—you will run into one of at least a dozen movies about killer asteroids. You know the obvious ones, Armageddon and Deep Impact, both from 1998. You might even be aware of the 1979 Sean Connery movie Meteor! (which sometimes has the exclamation mark after the name and sometimes doesn’t—its presence does not change the general crappiness of the film). But there are a ton of low-budget films that you probably never heard of. There is Meteor Storm, and Meteor Apocalypse, Impact, Without Warning, Meteorites!, A Fire in the Sky, Doomsday Rock, Falling Fire, and Asteroid. Both Meteor(!) and A Fire in the Sky date from the late 1970s. All the rest are from the late 1990s to the present, and were clearly inspired by the 1996 impact of comet Shoemaker-Levy 9 with Jupiter. You can bet good money that there will be more, especially as we approach our predicted doom in 2012.

But it turns out that the killer asteroid movie concept goes back farther than the 1970s—much farther. In 1958, Guido Giambartolomei produced The Day the Sky Exploded. You can be forgiven for not recognizing Giambartolomei’s name. He was an Italian producer, and this is an Italian movie, and possibly the great granddaddy of all killer asteroid flicks. It is also a rather lousy film, at times barely watchable, but fortunately only 80 minutes long. It was dubbed into English, sometimes effectively—they used Australian and Indian actors to reflect their native accents—and sometimes not, such as referring to retro-rockets as “retard rockets.”

The Day the Sky Exploded was written by Sandro Continenza and Marcello Coscia and directed by Paolo Hueusch. The cinematographer was Mario Bava, who directed Black Sunday in 1960 and quickly made a name for himself as a director of Italian horror movies. Bava’s cinematography does make the film more visually interesting than one would expect from a really low-budget Italian science fiction movie. Other than Bava, nobody from The Day the Sky Exploded seems to have left much of a mark on film history.

But where did the movie’s creators learn about the Tunguska explosion? And where did they come up with the idea of an asteroid impact causing widespread destruction on Earth? And where did they come up with the idea of using nuclear weapons atop missiles to take out the asteroid? Perhaps only an Italian science fiction film historian might be able to track down the answers.

The idea that asteroids could pose danger to human life is one that evolved slowly, over many decades. The giant Meteor Crater near Flagstaff, Arizona was not scientifically connected to a meteor until Eugene Shoemaker published his study results in 1960. The connection of an asteroid collision to at least one major extinction event in Earth’s history did not come until several decades after that—and the details are still under dispute. An obscure, long-forgotten, and not-very-good Italian science fiction film somehow connected a number of dots in 1958 that were still scattered throughout scientific literature, to the extent that they existed at all.

Link: The Space Review ("Italian doomsday: killer asteroids in 1958")

Link: YouTube Video (The Day The Sky Exploded (Part 1/9))

Link: Wikipedia Entry (The Day the Sky Exploded)

Link: IMDB (The Day The Sky Exploded)

Link: Archive.org (The Day The Sky Exploded)

BBC Horizon Documentary 2010 Asteroids The Good the Bad and the Ugly

BBC Horizon 2010 Asteroids The Good the Bad and the Ugly ¦ 720p HD [1/4]


BBC Horizon 2010 Asteroids The Good the Bad and the Ugly ¦ 720p HD [2/4]


BBC Horizon 2010 Asteroids The Good the Bad and the Ugly ¦ 720p HD [3/4]


BBC Horizon 2010 Asteroids The Good the Bad and the Ugly ¦ 720p HD [4/4]

Paper: "Accessibility of the resources of near Earth space using multi-impulse transfers"

"Accessibility of the resources of near Earth space using multi-impulse transfers"

Sanchez, J.P. and McInnes, Colin R. (2010) Accessibility of the resources of near Earth space using multi-impulse transfers. In: 2010 AIAA/AAS Astrodynamics Specialist Conference, 2-5 August 2010, Toronto, Canada. (Submitted)

Abstract: Most future concepts for exploration and exploitation of space require a large initial mass in low Earth orbit. Delivering this mass requires overcoming Earth's natural gravity well, which imposes a distinct obstacle to space-faring. An alternative for future space progress is to search for resources in-situ among the near Earth asteroid population. This paper examines the scenario of future utilization of asteroid resources. The near Earth asteroid resources that could be transferred to a bound Earth orbit are determined by integrating the probability of finding asteroids inside the Keplerian orbital element space of the set of transfers with an specific energy smaller than a given threshold. Transfers are defined by a series of impulsive maneuvers and computed using the patched-conic approximation. The results show that even moderately low energy transfers enable access to a large mass of resources.

Link: Reference (strathprints)

Link: Paper (PDF)

Link: planetarydefense.blogspot.com Google Docs library

Paper: "On the deflection of asteroids with mirrors"

Paper on the "mirror bees" asteroid mitigation concept.

"On the deflection of asteroids with mirrors"
Massimiliano Vasile and Christie Alisa Maddock, CELESTIAL MECHANICS AND DYNAMICAL ASTRONOMY, Volume 107, Numbers 1-2, 265-284, DOI: 10.1007/s10569-010-9277-3

Abstract: This paper presents an analysis of an asteroid deflection method based on multiple solar concentrators. A model of the deflection through the sublimation of the surface material of an asteroid is presented, with simulation results showing the achievable impact parameter with, and without, accounting for the effects of mirror contamination due to the ejected debris plume. A second model with simulation results is presented analyzing an enhancement of the Yarkovsky effect, which provides a significant deflection even when the surface temperature is not high enough to sublimate. Finally the dynamical model of solar concentrators in the proximity of an irregular celestial body are discussed, together with a Lyapunov-based controller to maintain the spacecraft concentrators at a required distance from the asteroid.

Link: Springer article reference

Link: planetarydefense.blgospot.com Google Docs library

Articles on Hayabusa Mission and Asteroid Particles Collection

Credit: JAXA

Selections from the article...

The Japan Aerospace Exploration Agency (JAXA) has confirmed that the tiny particles inside the Hayabusa spacecraft‘s sample return container are in fact from the asteroid Itokawa. Scientists examined the particles to determine if the probe successfully captured and brought back anything from the asteroid, and in a press release said “about 1,500 grains were identified as rocky particles, and most were determined to be of extraterrestrial origin, and definitely from Asteroid Itokawa.”

Previously, JAXA said that although particles were inside the container, it wasn’t clear if they were from the asteroid or if they could be of terrestrial origin (dust from Earth that could have been inside the container).

The particles samples were collected from the chamber by a specially shaped Teflon spatula and examined with a scanning electron microscope. There were two chambers inside the container, and from the press release (in Japanese) it appears all the particles were found in one chamber, Chamber A.

Most of the particles are extremely small, about 10 microns in size and require special handling and equipment. Unfortunately they aren’t the “peanut-sized” chunks of rock that the mission originally hoped to capture. This will make analyzing the particles difficult, but not impossible.

Link: Universe Today

Link: JAXA Press Release

Article: Asteroid 2010 WA Close Approach Update from 16 November 2010

This photo taken on Nov. 16, 2010 shows the asteroid 2010 WA as it passes within 24,000 miles (38,000 kilometers) as seen by astronomers using a telescope at the Magdalena Ridge Observatory in New Mexico. It is about 10 feet (3 meters) wide. Credit: Dr. William Ryan/Magdalena Ridge Observatory/2.4-meter Telescope/New Mexico Tech

Selections from the article...

The space rock, called asteroid 2010 WA, flew within 24,000 miles (38,000 kilometers) of Earth Tuesday night (Nov. 16).

The asteroid was tiny, just 10 feet (3 meters) across and posed no threat of hitting Earth. In fact, it was so small that it would break apart before passing through Earth's atmosphere, NASA scientists said.

Astronomers with the Magdalena Ridge Observatory near Socorro, N.M., trained a 2.4-meter telescope on the asteroid as it sailed past the Earth Tuesday at 10:44 p.m. EST (0344 Nov. 17 GMT).

What they found was surprising.

"We measured the rotation rate of the asteroid at about 31 seconds," astronomer Eileen Ryan, the observatory's director, told SPACE.com in an e-mail. "This makes it the second fastest rotating asteroid discovered to date."

The fastest spinning asteroid currently known is an asteroid called 2010 JL88, which spins once every 24.5 seconds and was also discovered using Magdalena Ridge Observatory's telescope, Ryan said.

Despite its small size, the asteroid still appeared as a bright object on a dark background in images taken by the observatory's telescope, which is built for tracking near-Earth objects (NEOs) and satellites, Ryan said.

"Because of this unusual feature, tracking fast-moving NEOs like 2010 WA is fairly easy for us," Ryan said.

The next time asteroid 2010 WA will come anywhere near Earth's cosmic neighborhood is in September 2013, but that pass will be considerably farther - about the equivalent of the distance between the Earth and the sun (93 million miles, or 150 million km), Ryan added.

Asteroid 2010 WA was the fourth space rock in three months to zip by the Earth within the orbit of the moon.

Link: Space.com article

Paper: "Rotational Mass Driver - an Efficient NEO Deflection Concept"

Source: Z. M. Ilitz, "Rotational Mass Driver — an Efficient NEO Deflection Concept"

Paper sent by the author on his NEO impact mitigation concept.

"Rotational Mass Driver - an Efficient NEO Deflection Concept"
by Z. M. Ilitz (Subotica, Serbia)

from
Protecting the Earth against Collisions with Asteroids and Comet Nuclei, Proceedings of the International Conference: "Asteroid-Comet Hazard–2009," Saint Petersburg, Russia, 2010.

Abstract:
There is an Olympic athletic discipline - throwing of a ball on a chain. This paper explores the possibility of using the same method for asteroid deflection. Instead of a chain, however, a tether (or a rope) must be used. As it turns out, the method has many merits. It offers high precision and controllability, is safe, efficient, and has a wide applicability range. The performance envelope for the rotational mass driver specifically covers binaries, rubble piles, and large objects on a direct collision course that need a delta-V of cm/s. The method is comparably efficient to nuclear methods, but is much safer.

Selections from the paper:

Space is a rather harsh environment, imposing strict limitations for tether material. However, there exists a material that fulfills all the needed criteria and is perfect for this job: “M5” fiber from DuPont, manufacturer of kevlar. The most important property of this material is that it is the only one that actually strengthens when exposed to UV radiation, while most of the others deteriorate if unprotected, sometimes very rapidly. Moreover it is resistant to temperatures encountered in Venus-like solar orbit, and it has tensile strength comparable to zylon (which needs coating protection against UV rays). A “comparably strong” zylon Z180 weights 2.44 kg/km, has a diameter of 1.02×3.43 mm, tensile strength of 5783 N, and a modulus of elasticity of 124 GPa [3]. Several other, less suitable choices exist, like PBI (material for spacesuits) or kevlar.

An attachment to the unknown, and probably unstable surface of the asteroid is needed. Considering how light-weight these tethers are, the idea is to loop them, like many “tentacles”, all the way around the asteroid. The spacecraft (S/C) will then mount the asteroid as a rider mounts a horse. To do this, tentacles are deployed in space during descend to the asteroid surface, and on touchdown their momentum will carry them, like whips, all around the surface (Fig. 1). Hereby, entanglement is a desired outcome, not a danger. The whole operation should last about 20 minutes, and the tentacles should only be kept from entangling each other during their deployment, not after that. Once they start whipping the asteroid, it is desirable for them to entangle on the opposite side to provide better attachment. For this purpose, they should be a little longer than necessary. Small hooks and bags of clay at their ends would ensure that they don't bounce back, but stay attached, securing the S/C. Usage of Hoytethers, and redundancy in their numbers provides safety against accidental cutting.

The best place to mount a NEO is on its lighted rotational pole (see Fig. 1). While this is not a requirement for this concept to work, the landing on a pole does makes things easier, as it also enables a “Tug boat” concept to be used as an alternative backup method of asteroid deflection.

Link: Planetarydefense.blogspot.com Google Docs

Article: "Administration to NASA: Defend Earth from Asteroids, Please"

Selections from Popular Mechanics article...

If you don't typically follow the debate on planetary defense, you could be forgiven for thinking Earth-crushing asteroids are more the stock in trade of big-budget action filmmakers than an actual concern for the taxpaying American. It might surprise you to learn that John Holdren, director of the White House's Office for Science and Technology Policy, recently wrote Congressional leaders to recommend that NASA spearhead a multi-agency effort to assess asteroid-deflection technologies.

But consider, for a moment, the following information regarding asteroids: In the previous 12 years—thanks to enhanced detection—the number of known near-Earth objects (NEOs) has grown from around 500 to upwards of 7000. Of those, approximately 20 percent are potentially hazardous to mankind, meaning that in the coming centuries, they conceivably could collide with the Earth.

But there's more, says former astronaut and PM editorial advisor, Tom Jones, who recently co-chaired a NASA Advisory Council task force on the subject of defending our planet from such calamitous celestial bodies.

"Remember, there are probably a million near-Earth asteroids out there that can come all the way through the atmosphere should they strike us," Jones says. "Twenty percent of a million is 200,000. So we have 200,000 potentially city-busting near-earth asteroids out there, and we know of only a tiny fraction of them."

With these frightening realities in mind, the eight-member Ad Hoc Task Force on Planetary Defense recommended ways in which NASA may address the threat of an NEO impact. Primary among them is establishing a Planetary Defense Coordination Office to begin in earnest the task of sifting through the options—strategies that currently include using a small spacecraft, called a gravity tractor, to pull an asteroid off-track; impacting it with a somewhat larger craft to knock it off course; and detonating a nuclear weapon near its surface to vaporize soil, propelling it in another direction.

Increasing the rate of discovery requires upgrades: Collaborating with the Air Force's Pan-STARR Telescope in Hawaii and the proposed Large Synoptic Survey Telescope (LSST) would be a good start. The task force also advocates launching a new space-based telescope. For about the cost of a typical NASA planetary mission, around $500 million, a tailor-made telescope would survey space for as-yet-unknown NEOs, potentially eliminating the mystery of what else is up there (and headed for us) in its first five years of operation.

Joe P. Hasler
12 November 2010
Popular Mechanics

Link: Article

Brian Geoffrey Marsden (1937-2010)

Retrospectives on Brian Geoffrey Marsden (1937-2010)

Press Announcement: Harvard-Smithsonian Center for Astrophysics (18 November 2010)

Post: Minor Planet Center (MPC) Announcement

Article: Scientific American Article ("Keeper of the Objects", 14 July 2003)

Post: Remembrance from Charlene Anderson (The Planetary Society)

Post: Discover Magazine Blog

Post: Sky and Telescope Blog

Post: New York Times ("Brian Marsden, Tracker of Comets, Dies at 73," 22 November 2010)

Credit: Harold Dorwin

 Image: © Roger Ressmeyer/CORBIS

Image: © Roger Ressmeyer/CORBIS

Although their views on Pluto's status were worlds apart, Clyde Tombaugh (left) and Brian Marsden were all smiles during this meeting outside Harvard Observatory in September 1987. Source: S&T: J. Kelly Beatty

Initial Update:

From Central Bureau for Astronomical Telegrams #2554 (also Simoastronomy blog entry):
Electronic Telegram No. 2554, Central Bureau for Astronomical Telegrams, INTERNATIONAL ASTRONOMICAL UNION, URL http://www.cbat.eps.harvard.edu/index.html. NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2010 CBAT, 2010 November 18 (CBET 2554) Daniel W. E. Green.

BRIAN G. MARSDEN (1937-2010)

It is with deep regret that we must announce the death today of Brian G. Marsden after a lengthy illness. He will be remembered as contributing much to celestial mechanics and the dynamics and orbits of minor bodies of the solar system and as having an encyclopedic knowledge of the history of astronomy. He was a dedicated servant to the astronomical community for many decades, serving as Director of the Central Bureau from 1968 to 2000 (and as Director Emeritus since then) and as Director of the Minor Planet Center from 1978 to 2006 (and as Director Emeritus since then). He also served extensively within Commissions 6 and 20 of the IAU over the years, being past President of both Commissions. And he was one of the most visible astronomers in the world over the years in terms of his generous availability to the news media on behalf of the astronomical community.

Link to Minor Planet Center announcement:

Brian Geoffrey Marsden was born on 1937 August 5 in Cambridge, England. His father, Thomas, was the senior mathematics teacher at a local high school. It was his mother, Eileen (nee West), however, who introduced him to the study of astronomy, when he returned home on the Thursday during his first week in primary school in 1942 and found her sitting in the back yard watching an eclipse of the sun. Using now frowned-upon candle-smoked glass, they sat watching the changing bite out of the sun. What most impressed the budding astronomer, however, was not that the eclipse could be seen, but the fact that it had been predicted in advance, and it was the idea that one could make successful predictions of events in the sky that eventually led him to his career.

When, at the age of 11, he entered the Perse School in Cambridge he was developing primitive methods for calculating the positions of the planets. He soon realized that earlier astronomers had come up with more accurate procedures for doing this over the centuries, and during the next couple of years this led to his introduction to the library of the Cambridge University Observatories and his study of how eclipses, for example, could be precisely computed. Together with a couple of other students he formed a school Astronomical Society, of which he served as the secretary. At the age of 16 he joined and began regularly attending the monthly London meetings of the British Astronomical Association. He quickly became involved with the Association's Computing Section, which was known specifically for making astronomical predictions other than those that were routinely being prepared by professional astronomers for publication in almanacs around the world. Under the watchful eyes of the director and assistant director of the Computing Section, this led him to prepare and publish predictions of the occasions when one of Jupiter's moons could be seen to pass directly in front of another. He also calculated the gravitational effects of the planets on the dates and sky positions of the returns of some periodic comets. He carried out these computations using seven-place logarithms. After all, this was long before pocket calculators had been invented, and the construction of large electronic computers was still then very much in its infancy. He always maintained that making such computations by primitive means significantly increased one's understanding of the science involved. During his last year of high school he also became a junior member of the Royal Astronomical Society.

He was an undergraduate at New College, University of Oxford. In his first year there he persuaded the British Astronomical Association to lend him a mechanical calculating machine, allowing him thereby to increase his computational productivity. By the time he received his undergraduate degree, in mathematics, he had already developed somewhat of an international reputation for the computation of orbits of comets, including new discoveries. He spent part of his first two undergraduate summer vacations working at the British Nautical Almanac Office. He also responded to an inquiry from Dorothy L. Sayers involving the ancient Roman poet Lucan. Incensed by what she perceived as grossly unfair criticism of Lucan by A. E. Housman and Robert Graves, she elicited his assistance during the last year of her life to support her view that Lucan's understanding of astronomy and geography was reasonably valid. Dr. Sayers' extensive correspondence in the course of this study is included in the last volume of her collected letters.

After Oxford, he took up an invitation to cross the pond and work at the Yale University Observatory. He had originally planned to spend just a year there carrying out research on orbital mechanics, but on his arrival in 1959 he was also enrolled as a Yale graduate student. With the ready availability of the university's IBM 650 computer in the observatory building, he had soon programmed it to compute the orbits of comets. Recalling his earlier interest in Jupiter's moons, he completed the requirements for his Ph.D. degree with a thesis on "The Motions of the Galilean Satellites of Jupiter".

At the invitation of director Fred Whipple, he joined the staff of the Smithsonian Astrophysical Observatory in Cambridge (MA) in 1965. Dr. Whipple was probably best known for devising the "dirty snowball" model for the nucleus of a comet a decade and a half earlier. At that time there was only rather limited evidence that the motion of a comet was affected by forces over and above those of gravitation (limited because of the need to compute the orbit by hand), and the Whipple model had it that those forces were due to the comet's reaction to vaporization of the cometary snow or ice by solar radiation. Dr. Marsden therefore developed a way to incorporate such forces directly into the equations that governed the motion of a comet. Application of a computer program that included these nongravitational effects to several comets soon gave results that were nicely compatible with Dr. Whipple's original idea. Continued refinement of the nongravitational terms, much of it done in collaboration with Zdenek Sekanina, a Czech astronomer and friend of Dr. Marsden whom he and Dr. Whipple succeeded in bringing to the U.S. as a refugee following the Soviet invasion of Prague in 1968, resulted in a wealth of improved computations of cometary orbits by the time Dr. Sekanina moved to California in 1980. It is noteworthy that the procedure devised and developed by Dr. Marsden is still widely used to compute the nongravitational effects of comets, with relatively little further modification by other astronomers.

The involvement of the Smithsonian Astrophysical Observatory with comets had been given a boost, shortly before Dr. Marsden's arrival there, by the transfer there from Copenhagen of the office of the Central Bureau for Astronomical Telegrams, a quaintly named organization that was established by the International Astronomical Union soon after its founding in 1920. The CBAT is responsible for disseminating information worldwide about the discoveries of comets, novae, supernovae and other objects of generally transient astronomical interest. It is the CBAT that actually names the comets (generally for their discoverers), and it has also been a repository\ for the observations of comets to which orbit computations need to be fitted. Dr. Marsden succeeded Dr. Owen Gingerich as the CBAT director in 1968. He was joined by Daniel Green as a student assistant a decade later, and Dr. Green took over as CBAT director in 2000. Until the early 1980s the Bureau really did receive and disseminate the discovery information by telegram (with dissemination also by postcard Circular), although e-mail announcements then understandably began to take over. The last time the CBAT received a telegram was when Thomas Bopp sent word of his discovery of a comet in 1995. Since word of this same discovery had already been received from Alan Hale a few hours earlier by e-mail, the object was very nearly just named Comet Hale, rather than the famous Comet Hale-Bopp that beautifully graced the world's skies for several weeks two years later.

The comet prediction of which he was most proud was of the return of comet Swift-Tuttle, which is the comet associated with the Perseid meteors each August. It had been discovered in 1862, and the conventional wisdom was that it would return around 1981. He followed that line for much of a paper he published on the subject in 1973. He had a strong suspicion, however, that the 1862 comet was identical with one seen in 1737, and this assumption allowed him to predict that Swift-Tuttle would not return until late-1992. This prediction proved to be correct, and this comet has the longest orbital period of all the comets whose returns have been successfully predicted.

Although the CBAT also traditionally made announcements of the discoveries of asteroids that came close to the earth, the official organization for attending to discoveries of asteroids (more than 99% of which are located in a belt between Mars and Jupiter) is the Minor Planet Center. Also operated by the International Astronomical Union, the MPC was located until 1978 at the Cincinnati Observatory. In that year the director, Dr. Paul Herget, was retiring, and it was necessary for the Center to find a new home. Accordingly, the IAU asked Dr. Marsden also to take over the direction of the MPC. Thanks to the transfer of associate director Conrad Bardwell with the MPC records from Cincinnati, this task was rendered easier. While the CBAT and the MPC still maintained their separate entities, there was a lot of common ground between them. Dr. Marsden was therefore able to introduce some efficiencies into their combined operation. On Mr. Bardwell's retirement at the end of 1989, Gareth Williams joined the MPC staff and later became associate director.

The advances in electronic communication during the 1990s also permitted improvements in MPC operation. Perhaps the most important of these was the development, in 1996, of the Internet "Near-Earth Object Confirmation Page". This draws attention to candidate earth-approaching objects in need of follow-up observations as soon as they have been reported to the MPC, following the derivation by Dr. Marsden of a particularly ingenious method for estimating the uncertainty of the prediction by automatically computing a series of orbits that represent just the first and the last observations. In 1998 he developed a certain amount of notoriety by suggesting that an object called 1997 XF11 could collide with the earth. He did this as a last-ditch effort to encourage the acquisition of further observations, including searches for possible data from several years earlier. The recognition of some observations from 1990 made it quite clear that there could be no collision with 1997 XF11 during the foreseeable future. Without those 1990 observations, however, the object's orbit would have become very uncertain following a close to moderate approach to the earth in 2028; indeed, Dr. Marsden correctly demonstrated that there was the possibility of an earth impact in 2040 and in several neighboring years. He was thereby able eventually to persuade his principal critics routinely to perform similar uncertainty computations for all near-earth objects as they were announced. Again, as more data accrue, it is almost certain to happen that all possible impacts with moderately large objects (i.e., those at least several hundred feet across) during the next century, say, will disappear. While the production of such computations was directly due to his encouragement, it was always with some amusement that he saw cases where further data forced his former critics sheepishly to withdraw their earlier frightening statements about a potentially dangerous object.

Dr. Marsden was particularly fascinated by the appearance of a group of comets that passed close to the sun. Known as members of the Kreutz group, after a German astronomer who studied them in the late nineteenth century, the discovery of three more of these sungrazing comets in the mid-twentieth century led him to undertake a detailed examination of how the individual comets may have evolved from each other. He published this examination in 1967, following it up with a further study in 1989 involving a more recent bright Kreutz comet, as well as several much fainter objects that had been detected from sun-observing coronagraphs out in space. Beginning in 1996, these were being found by the SOHO coronagraphs at rates ranging from a few dozen to more than one hundred per year. Unfortunately, the faintness of the comets and the poor accuracy with which they could be measured made it difficult to establish their orbits as satisfactorily as Dr. Marsden would have liked. More significantly, however, he was able to recognize that the SOHO data also contained another group of comets with similar orbits, these comets now known as members of the "Marsden group". Unlike the individual Kreutz comets, which have orbital periods of several centuries, it seems that the Marsden comets have orbital periods of only five or six years, leading him to try and recognize the same object at different passages near the sun and thereby predict future returns. Two other well-populated groups have also been detected in the SOHO data.

Another series of astronomical discoveries that greatly interested him were what he always called the "transneptunian objects", although many of his colleagues have insisted on calling them "objects in the Kuiper Belt". When what those same colleagues considered to be the first of these was discovered in 1992, Dr. Marsden immediately remarked that this was untrue, because Pluto, discovered in 1930 and admittedly somewhat larger in size, had to be the first. More specifically, he was the first to suggest, correctly, that three further transneptunian objects discovered in 1993 were exactly like Pluto in the sense that they all orbit the sun twice while Neptune orbits it thrice. This particular recognition set him firmly on the quest to "demote" Pluto. Success required the discovery of transneptunian objects more comparable to Pluto in size, something that finally happened in 2005 with the discovery of the object that came to be known as Eris. At its triennial meeting in 2006 in Prague, the IAU voted to designate these objects, together with two further transneptunian objects now known as Makemake and Haumea, as well as the largest asteroid, Ceres, members of a new class of "dwarf planet".

It was also at the IAU meeting in Prague that Dr. Marsden stepped down as MPC director, and he was quite entertained by the thought that both he and Pluto had been retired on the same day. While he remained working at the MPC (and also the CBAT) in an emeritus capacity, the directorship was passed to Dr. Timothy Spahr, whom he had brought to the MPC in 2000.

Dr. Marsden served as an associate director of the Harvard-Smithsonian Center for Astrophysics (the combination of the Smithsonian Astrophysical Observatory and the Harvard College Observatory) for 15.75 years from the beginning of 1987 (the longest tenure for any of the Center's associate directors). He was chair of the Division of Dynamical Astronomy of the American Astronomical Society during 1976-1978 and president of the IAU commissions that oversaw the operation of the minor Planet Center (1976-1979) and the Central Bureau for Astronomical Telegrams (2000-2003). He continued to serve subsequently on the two solar-system nomenclature committees of the IAU, being the perennial secretary of the one that decides on names for asteroids. He also continued to publish a "Catalogue of Cometary Orbits", the first of these having appeared in 1972 and its successors roughly at intervals of two years.

Among the various awards he received from the U.S., the U.K. and a handful of other European countries, the ones he particularly appreciated were the 1995 Dirk Brouwer Award (named for his mentor at Yale) of the AAS Division on Dynamical Astronomy and the 1989 Van Biesbroeck Award (named for an old friend and observer of comets and double stars), then presented by the University of Arizona, now by the AAS, for service to astronomy.

Dr. Marsden married Nancy Lou Zissell, of Trumbull, Connecticut, on 1964 December 26, and fathered Cynthia (who is married to Gareth Williams, still MPC associate director), of Arlington, Massachusetts; and Jonathan, of San Mateo, California. There are three Californian grandchildren, Nikhilas, Nathaniel and Neena. A sister, Sylvia Custerson, continues to reside in Cambridge, England.

From Wikipedia:

Brian Geoffrey Marsden (born 5 August 1937, died 18 November 2010) was a British astronomer born in Cambridge, England, and educated at Oxford and Yale. Dr. Marsden was the longtime director of the Minor Planet Center (MPC) at the Harvard-Smithsonian Center for Astrophysics (director emeritus from 2006 to 2010).

He specialized in celestial mechanics and astrometry, collecting data on the positions of asteroids and comets and computing their orbits, often from minimal observational information and providing their future positions on International Astronomical Union (IAU) circulars. In addition to serving as MPC director since 1978, he served as the director of the Central Bureau for Astronomical Telegrams (CBAT) from 1968 to 1999.

Marsden helped recover once lost asteroids and lost comets. Some asteroid and comet discoveries of previous decades were "lost" because not enough observational data had been obtained at the time to determine a reliable enough orbit to know where to look for re-observation at future dates. Occasionally, a newly discovered object turns out to be a rediscovery of a previously lost object, which can be determined by calculating its orbit backwards into the past and matching calculated positions with the previously recorded positions of the lost object. In the case of comets this is especially tricky because of nongravitational forces that can affect their orbits (one of which is emission of jets of gas from the comet nucleus), but Marsden has specialized in calculating such nongravitational forces. Notably, he successfully predicted the 1992 return of the once-lost periodic comet Swift-Tuttle.

He once proposed that Pluto should be cross-listed as both a planet and a minor planet and assigned the asteroid number 10000; however, this proposal was not accepted. A similar proposal was, however, finally accepted in 2006 when Pluto was designated minor planet 134340 and also declared a dwarf planet.

Link: Wikipedia (Brian G. Marsden)

Link: Article from from Universe Today

Link: Press Announcement: Harvard-Smithsonian Center for Astrophysics (18 November 2010)

Link: Scientific American Article ("Keeper of the Objects", 14 July 2003)

Link: Remembrance from Charlene Anderson (The Planetary Society)

Paper: "Mission feasibility analysis on deflecting Earth-crossing objects using a power limited laser ablating spacecraft"

Mission feasibility analysis on deflecting Earth-crossing objects using a power limited laser ablating spacecraft

Advances in Space Research, Volume 45, Issue 1, p. 123-143

Authors: Song, Young-Joo; Park, Sang-Young; Choi, Kyu-Hong

Affiliation: AA(Astrodynamics and Control Laboratory, Department of Astronomy, Yonsei Universit

Abstract: This paper analyzes several mission capabilities to deflect Earth-crossing objects (ECOs) using a conceptual future spacecraft with a power limited laser ablating tool. A constrained optimization problem is formulated based on nonlinear programming with a three-dimensional patched conic method. System dynamics are also established, considering the target ECO’s orbit as being continuously perturbed by limited laser power. The required optimal operating duration and operating angle history of the laser ablating tool are computed for various types of ECOs to avoid an Earth impact. The available final warning time is also determined with a given limited laser power. As a result, detailed laser operating behaviors are presented and discussed, which include characteristics of operating duration and angle variation histories in relation to the operation’s start time and target object’s properties. The calculated durations of the optimal laser operation are also compared to those estimated with first-order approximations previous studies. It is discovered that the duration of the laser operation estimated with first-order approximations could result in up to about 50% error if the operation is started at the final warning time. The laser operation should be started as early as possible because an early start requires a short operating duration with a small operating angle variation. The mission feasibility demonstrated in the present study will give various insights into preparing future deflection missions using power limited spacecraft with a laser ablation tool.

Link: Paper

Link: AIAA Paper

Paper: "ASTEROIDFINDER – THE SPACE-BORNE TELESCOPE TO SEARCH FOR NEO"

ASTEROIDFINDER – THE SPACE-BORNE TELESCOPE TO SEARCH FOR NEO

International Conference on Space Optics 4 - 8 October 2010, Rhodes, Greece

Authors: M. Hartl, H. Mosebach, J. Schubert, H. Michaelis, S. Mottola, E. Kührt, K. Schindler

Abstract: This paper presents the mission profile as well as the optical configuration of the space-borne AsteroidFinder telescope. Its main objective is to retrieve asteroids with orbits interior to the earth’s orbit. The instrument requires high sensitivity to detect asteroids with a limiting magnitude of equal or larger than 18.5mag (V-Band) and astrometric accuracy of 1arcsec (1σ). This requires a telescope aperture greater than 400cm2, high image stability, detector with high quantum efficiency (peak > 90%) and very low noise, which is only limited by zodiacal background. The telescope will observe the sky between 30° and 60° in solar elongation. The telescope optics is based on a Cook type TMA. An effective 2°×2° field of view (FOV) is achieved by a fast F/3.4 telescope with near diffraction-limited performance. The absence of centre obscuration or spiders in combination with an accessible intermediate field plane and exit pupil allow for efficient stray light mitigation. Design drivers for the telescope are the required point spread function (PSF) values, an extremely efficient stray light suppression (due to the magnitude requirement mentioned above), the detector performance, and the overall optical and mechanical stability for all orientations of the satellite. To accommodate the passive thermal stabilization scheme and the necessary structural stability, the materials selection for the telescope main structure and the mirrors are of vital importance. A focal plane with four EMCCD detectors is envisaged. The EMCCD technology features shorter integration times, which is in favor regarding the pointing performance of the satellite. The launch of the mission is foreseen for the year 2013 with a subsequent mission lifetime of at least 1 year.

Link: Paper

Article on Asteroid 2010 WA (3 meter diameter): Close Approach at 10:44 p.m. EST (0344 GMT) on 16 November 2010, missing by 38,000 kilometers

Article on recent NEO close approaches to the Earth, selections from the article...

A tiny asteroid will zip close by Earth tonight (Nov. 16) at a range much closer than the moon, but poses no threat of striking our planet or even entering the atmosphere, NASA has announced.

The asteroid 2010 WA will pass Earth at 10:44 p.m. EST (0344 GMT), missing the planet by about 24,000 miles (38,000 kilometers), NASA's asteroid-watching team wrote on Twitter. It is nearly 10 feet (3 meters wide), so small it would simply break apart if it encountered Earth's atmosphere.

NASA officials said the asteroid is a "very small space rock" that will pass the Earth at roughly one-tenth the distance between our planet and the moon, according to NASA's AsteroidWatch Twitter feed. [5 Reasons to Care About Asteroids]

On average, the moon is about roughly 238,900 miles (384,402 km) from Earth. Some of the highest satellites above Earth fly in geostationary positions about 22,370 miles (36,000 km) up. The International Space Station sails through space about 220 miles (354 km) above Earth.

Asteroid 2010 WA is the fourth space rock in as many months to buzz harmlessly by the Earth within the moon's orbit. The asteroid 2010 TD54 passed the planet at nearly the same miss distance on Oct. 12. In September, a rare sighting of two asteroids – called 2010 RX30 and 2010 RF12 – was spotted when they both passed within the moon's orbit on the same day (Sept. 8).

Like 2010 WA, those earlier asteroid flybys posed no threat to Earth and most were small enough that they would burn up in the atmosphere if they hit it.

"Still, a good practice in detection," NASA's asteroid-tracking team wrote of 2010 WA on Twitter.

An asteroid about 16.5 feet (5 meters) across can be expected to pass Earth inside the orbit of the moon about once a day, NASA scientists have said. They typically enter Earth's atmosphere about once every two years, they added.

Bigger asteroids of about 460 feet (140 meters) wide can cause widespread damage around their impact sites. But much larger space rocks would have to strike Earth to cause global devastation.

There are an estimated 30 million unknown asteroids in our solar system, NASA has said.

Asteroid 2010 WA is not even the first space rock to slip by the Earth-moon system this month.

On Nov. 9, the small asteroid 2010 VL65 passed the Earth at a range of 610,000 miles (980,000 km) – about 2 1/2 times the distance between our planet and moon, NASA officials said. That asteroid was only 23 feet (7 meters) across – small enough to burn up completely in the atmosphere – and was only visible to seasoned skywatchers with telescopes.

NASA routinely tracks asteroids and comets that fly near Earth as part of its Near-Earth Object Observations program, which uses a network of ground and space telescopes to monitor the space rock environment around the planet. To date, the program has tracked about 85 percent of the largest asteroids that fly near Earth and 15 percent of asteroids in the 460-foot class, according to the latest report.

The U.S. space agency also plans to send astronauts to an asteroid by 2025 under a space plan ordered by President Obama. The mission could help scientists better understand the composition of asteroids, as well as develop better methods of deflecting them before they pose a threat to Earth, agency officials have said.

Small Asteroid to Give Earth a Close Shave
Tariq Malik
SPACE.com Managing Editor
posted: 16 November 2010

Link: Article

October 2010 Issue of Cosmic Research Journal: Multiple NEO Papers

October 2010 issue (Volume 38 / 2000 - Volume 48 / 2010) of Cosmic Research has multiple papers on NEOs and planetary defense:

On coordinated approach to the problem of asteroid-comet impact hazard
B. M. Shustov

The space situational awareness program of the European Space Agency
N. Bobrinsky and L. Del Monte

The near-Earth objects segment of the european space situational awareness program
G. Drolshagen, D. Koschny and N. Bobrinsky

Relevance of asteroid occultation measurements to determination of characteristics of near-Earth objects
D. Koschny, J. Drolshagen and N. Bobrinsky

Investigation of the motion of (99942) apophis asteroid using the SKIF cyberia multiprocessor computing system
L. E. Bykova and T. Yu. Galushina

Estimation of the determination accuracy of orbit parameters of the apophis asteroid from measurement results
B. Ts. Bakhshiyan, A. A. Sukhanov and K. S. Fedyaev

Using Venus for locating space observatories to discover potentially hazardous asteroids
D. W. Dunham and A. L. Genova

A permanently-acting NEA damage mitigation technique via the Yarkovsky effect
D. C. Hyland, H. A. Altwaijry, S. Ge, R. Margulieux and J. Doyle, et al.

A mission template for exploration and damage mitigation of potential hazard of Near Earth Asteroids
D. C. Hyland, H. A. Altwaijry, R. Margulieux, J. Doyle and J. Sandberg, et al.

The Aster project: Flight to a near-Earth asteroid
A. A. Sukhanov, H. F. de C. Velho, E. E. Macau and O. C. Winter

Instruments and methods of discovering hazardous asteroids by ground-based and space optical devices
V. G. Kurt

Storing and processing astrometric and photometric data on NEA: Current state and future in Russia
S. A. Naroenkov

A method of controlling asteroid collision with the Earth
E. A. Gonzaga

ESA research and development activity on SSA-NEO preliminary definition
R. Franco

Estimation of accuracy of close encounter performed by the bootstrap method
J. Desmars, J. -E. Arlot and A. Vienne

Gravitational maneuvers as a way to direct small asteroids to trajectory of a rendezvous with dangerous near-Earth objects
R. R. Nazirov and N. A. Eismont

Link: Cosmic Research journal page

Paper: Initial Parameter Study of the Response of Simple Asteroid or Cometary Nuclei Models to a Nuclear Burst

Title: Initial Parameter Study of the Response of Simple Asteroid or Cometary Nuclei
Models to a Nuclear Burst

Authors: P. A. Bradley1, C. S. Plesko1,2, R. P. Weaver1, R. R. C. Clement1, J. A. Guzik1, L. A. Pritchett-Sheets1, and W. F. Huebner3, 1Applied Physics Division, MS T087, Los Alamos National Laboratory (pbradley@lanl.gov), 2U. C. Santa Cruz Earth and Planetary Sciences Dept., and 3Southwest Research Institute

Abstract: There is much popular press about Potentially Hazardous Objects (PHOs) and how to mitigate their threat. The two mitigation options are destruction or deflection of the PHO. Presently, the most technically feasible method of deflection is a nuclear stand-off burst [1]. However, many questions remain as to the response of an asteroid or comet to a nuclear burst. Recent increases in computing power and scientific understanding of the physical properties of asteroids and comets make it possible to numerically simulate the response of these porous and inhomogeneous bodies to strong shocks and radiation. Here we use the radiation-hydrocode RAGE to explore the coupling of radiation energy from a nuclear burst to a grid of simplified PHO models. We use simple 2-D axisymmetric models of 100 m diameter spherical PHOs composed of different materials to study their response to nuclear bursts of 10, 100, and 1000 kt with distances of 20 and 70 m.

From paper...

Even with our simplified models, we see that bursts of about 10 kt will be effective in deflecting a 100 m diameter solid PHO away from Earth if the lead time is about 1 to 4 years. Assuming there is no issue with fragmentation, our calculations of a 100 kt burst 20 m from a target PHO show that it is capable of deflecting a PHO with no more than 4 months of lead time. We will need to run similar calculations for PHO models that have a realistic shape, composition, rotation rate, strength, and porosity for ”playbook” entries.

Link: Paper Reference

Link: Paper (PDF)

Paper: Solar radiation pressure on (99942) Apophis

Title: Solar radiation pressure on (99942) Apophis

Authors: J. Žižkaa, b, and D. Vokrouhlickýa, ,
a Institute of Astronomy, Charles University, V Holešovičkách 2, 18000 Prague 8, Czech Republic
b Nicholas Copernicus Observatory and Planetarium, Kravı´ hora 2, 61600 Brno, Czech Republic

Abstract: Near-Earth asteroid (99942) Apophis currently resides among the top positions on the list of objects with small, yet non-zero impact probability with the Earth. For that reason an unusual observational and theoretical effort has been dedicated to precisely characterize its future orbit. Here we discuss orbital perturbation of Apophis due to incident and reflected solar radiation pressure (SRP). We both revisit recent analytical estimate of the SRP effects for this body and also formulate a numerical approach allowing us to compute the SRP orbital perturbation under general assumptions. Contrary to some previous results, we show that SRP has a much smaller effect on the Apophis trajectory than does the thermal re-radiation force which produces the Yarkovsky effect. When the Yarkovsky effect becomes constrained enough in the future, our approach may be used to improve the orbit determination for this asteroid.

Link: Paper

Link: Article ("Apophis asteroid encounter in 2013 should help answer impact worries")

Article on recent meeting in Europe on Mission Planning and Operations Group (MPOG): Continued discussion on global coordinating group for planetary defense

Article from Leonard David on the recent meeting to discuss the proposals for a global Mission Planning and Operations Group (MPOG) at the European Space Agency's European Space Operations Center on October 27-29, 2010. Selections from the article...

To help focus a world-class planetary defense against threatening near-Earth objects, the space experts are seeking to establish a high-level Mission Planning and Operations Group, or MPOG for short.

Veteran astronauts and space planners gathered here at the European Space Agency's European Space Operations Center Oct. 27-29 to shape the asteroid threat response plan and establish an Information Analysis and Warning Network.

While the technical issues – early warning and deflection – are challenging, they essentially pale in comparison with the very sticky issues that will confront the community of nations when they have to make a collective decision to act on an actual threat, Schweickart told SPACE.com. [5 Reasons to Care About Asteroids]

"This really has to be a collective decision," Schweickart said, "since, in the deflection process, there will be a trail of nations across which the impact point moves as we shift it off the Earth."

The space agencies in the MPOG workshop grappled with the questions of what would have to be performed and how they would do it, Schweickart said, "either as the 'designated hitter,' as it were ... or collectively in some way. These are difficult geopolitical challenges, and the workshop provided the first face-to-face setting for many of the space agencies to grapple with it together."

The workshop touched upon a number of strategies to deflect an incoming object, but there was also discussion of using a "physics package," space slang for a nuclear bomb if need be. There remains a good deal of discussion over which deflection strategy best serves the planet and humankind – if time is on our side.

In a post-workshop handout, the attendees concluded that:

- A Mission Planning and Operations Group should be established.

- The MPOG should identify to space agencies the technical issues involved in planetary defense, to take advantage of synergies between human exploration, science, and study of the NEO hazard.

- The MPOG should propose research themes in NEO deflection for use by space agencies, addressing those areas most critical for effective deflection strategies.

- There is great value in finding hazardous NEOs early, to reduce the costs of deflection missions. Early detection would require upgraded NEO search and tracking capabilities.

The results of the workshop will be folded into the ongoing work of the United Nations Committee on the Peaceful Uses of Outer Space in its sessions next spring and summer. This will all come together as a set of recommendations or procedures that will be put before the U.N. General Assembly in about a year.

Link: Space.com article

Rusty Schweickart's Lecture at Stanford: "The Asteroid Challenge: Will We Be Ready?"

Guest lecturer Rusty Schweickart gives a lecture entitled, "The Asteroid Challenge: Will We Be Ready?" for Professor Lynn Rothschild's Astrobiology and Space Exploration course.

Link: YouTube (The Asteroid Challenge: Will We Be Ready?)

National Geographic Documentary on Asteroid Threat and 2008 TC3

Purdue University's 'Impact: Earth!' asteroid impact effects calculator

The parameters screen of the "Impact: Earth!" website allows users to input the diameter and density of the projectile, the impact angle and velocity, and whether the projectile will hit water or rock. (Information Technology at Purdue image/Michele Rund)

The results screen shows users the likely scenario of their impact, including crater size, seismic effects, air blast, energy equivalent and global damage. (Information Technology at Purdue image/Michele Rund)

From the Purdue University press release....

Purdue University on Wednesday (Nov. 3) unveiled ''Impact: Earth!'' a new website that allows anyone to calculate the potential damage a comet or asteroid would cause if it hit the Earth.

The interactive website is scientifically accurate enough to be used by homeland security and NASA, but user-friendly and visual enough for elementary school students, said Jay Melosh, the distinguished professor of earth and atmospheric sciences and physics at Purdue who led the creation of the impact effects calculator.

''The site is intended for a broad global audience because an impact is an inevitable aspect of life on this planet and literally everyone on Earth should be interested,'' said Melosh, who is an expert in impact cratering. ''There have been big impacts in the past, and we expect big impacts in the future. This site gives the lowdown on what happens when such an impact occurs.''

More than 100 tons of material from asteroids and comets hits the Earth every day, he said. Even fragments as large as a sedan hurtle toward the planet a few times each year, but these burn up as they enter the atmosphere.

''Fairly large events happen about once a century,'' Melosh said. ''The biggest threat in our near future is the asteroid Apophis, which has a small chance of striking the Earth in 2036. It is about one-third of a mile in diameter, and the calculator will tell what will happen if it should fall in your backyard.''

Users first enter a few parameters such as the diameter of the impact object, its density, velocity, angle of entry and where it will hit the Earth. The site then estimates the consequences of its impact, including the atmospheric blast wave, ground shaking, size of tsunami generated, fireball expansion, distribution of debris and size of the crater produced. The calculator is available at http://www.purdue.edu/impactearth

Massive asteroids, like the 9-mile-wide Chicxulub that killed the dinosaurs 65 million years ago, are very rare, but smaller and more common asteroids have left craters that remain today. For instance, Arizona's famous Barringer Crater - nearly a mile wide - is evidence of an impact 50,000 years ago from an asteroid estimated to be 164 feet in diameter and composed of nickel and iron.

According to the impact calculator, if an asteroid of similar composition but twice as large hit about 20 miles outside of Chicago, the impact energy would be equivalent to about 97 megatons of TNT. The resulting crater would be almost two miles wide and the impact would ignite a fireball with a one-mile radius. A magnitude 6 earthquake would shake the city approximately six seconds after impact, the air blast would shatter windows, and the Windy City would be coated in a fine dust of ejecta. The site states that impacts of this size occur roughly once every 15,000 years.

"Impact: Earth" is a more visual and user-friendly update to an impact calculator Melosh created with Robert Marcus and Gareth Collins about eight years ago while at the University of Arizona. Melosh and Collins collaborated with Information Technology at Purdue (ITaP) to update the program and create a graphic interface to make the site easier and more fun to use, he said.

''There were a lot of requests for calculations of tsunamis that would be produced from an ocean impact, and we've added that,'' said Collins, who is a natural environment research council fellow at Imperial College London. ''In addition, the program now visually illustrates the information the user enters, and we plan to connect the program with GoogleEarth to show a map of the effects.''

John Spray, director of the planetary and space science center at the University of New Brunswick in Canada, said the impact calculator is a valuable source for the scientifically accurate reconstruction of impact effects.

"This calculator is a critical tool for determining the potential consequences of an impact," said Spray, who also runs the Earth Impacts Database of confirmed impact craters. "It is widely used by government and scientific agencies, as well as impact research groups and space enthusiasts throughout the world."

In the week after the first impacts effects calculator launched there were 10 million hits from around the world. Today governmental agencies link to and use the site, including the Department of Homeland Security, NASA, the U.S. Geological Survey and the U.S. Air Force. The program is available in multiple languages and also is used by foreign governmental agencies, Melosh said.

"It is a valuable tool to quantify the important impact processes that might affect the people, buildings and landscape in the vicinity of an impact event," he said. "With the program we include a scientific paper that describes the approximations and equations and discusses the uncertainty in our predictions. One can delve as much into the science as they would like."

The calculator also has been a valuable tool in sparking young students' interest in science, Melosh said.

"The calculator has been used by teachers and students from kindergarten through high school both for school projects and for fun," he said. "At one point we debated whether or not to use scientific notation in the results, but a teacher asked us to keep it. She told us that it inspired her class and the students worked hard to learn the method so they could fully understand the results."

The ''Impact:Earth!'' calculator website was developed by Information Technology at Purdue (ITaP), which develops online tools to support learning and scientific discovery, including the nationally acclaimed classroom technologies HotSeat and Mixable. The site will be updated with additional features in coming months, according to the team.

Melosh is part of the science team of NASA's EPOXI mission that will be evaluating the comet Hartley 2 on Thursday (Nov. 4). The mission uses the Deep Impact spacecraft that will fly to within 434 miles of the comet. This will be only the fifth time in history that a spacecraft has been close enough to take images of a comet's center.

"Comets and asteroids have become a part of our popular culture, but we don't really know a lot about their composition and internal processes as they fly through space," Melosh said. "We have much more to learn about these objects that are often our closest neighbors in space. We do know that sometimes they enter into a collision course with the Earth, and this site offers an authoritative place to go to learn about the detailed effects of an impact."

The older version of the impact calculator, which may be easier to use for those with a slow Internet connection or older computer, is available at http://impact.ese.ic.ac.uk

Link: Impact Earth Website from Purdue University

Link: Purdue University Press Release