This area will cover relevant news of the threat to the planet from Near Earth Objects (NEOs) including concepts and designs for mitigation. All opinions are those of the author.
University of Calgary graduate student Ellen Milley poses with a fragment of a meteorite in a small pond near Lloydminster, Sask., Canada Friday, Nov. 28, 2008. Scientists said Friday they had found remains of a meteor that illuminated the sky before falling to earth in western Canada earlier this month. University of Calgary scientist Alan Hildebrand and Milley found several meteor fragments near the Battle River along the rural Alberta-Saskatchewan border, near the city of Lloydminster late Thursday. (AP Photo/The Canadian Press, Geoff Howe)
A woman's hand, to show the scale, is seen by what scientists say is a fragment of a meteorite found in a small pond near Lloydminster, Sask., Canada Friday, Nov. 28, 2008. Scientists said Friday they had found remains of a meteor that illuminated the sky before falling to earth in western Canada earlier this month. University of Calgary scientist Alan Hildebrand and graduate student Ellen Milley found several meteor fragments near the Battle River along the rural Alberta-Saskatchewan border, near the city of Lloydminster late Thursday. (AP Photo/The Canadian Press, Geoff Howe)
From the article...
Scientists said Friday they had found remains of a meteor that illuminated the sky before falling to earth in western Canada earlier this month.
University of Calgary scientist Alan Hildebrand and graduate student Ellen Milley found several meteor fragments near the Battle River along the rural Alberta-Saskatchewan border, near the city of Lloydminster late Thursday.
They said there could be thousands of meteorite pieces strewn over a 7-square-mile area of mostly flat, barren land, with few inhabitants.
From a recent paper on using LIDAR to find meteor impacts on the Earth...
Anatomy of a young impact event in central Alberta, Canada: Prospects for the missing Holocene impact record Geology Volume 36, Issue 12 (December 2008) Article: pp. 955–958 C.D.K. Herd, D.G. Froese, E.L. Walton, R.S. Kofman, E.P.K. Herd, and M.J.M. Duke
Abstract: Small impact events recorded on the surface of Earth are significantly underrepresented based on expected magnitude-frequency relations. We report the discovery of a 36-m-diameter late Holocene impact crater located in a forested area near the town of Whitecourt, Alberta, Canada. Although undetectable using visible imagery, the presence of the crater is revealed using a bare-Earth digital elevation model obtained through airborne light detection and ranging (LiDAR). The target material comprises deglacial Quaternary sediments, with impact ejecta burying a late Holocene soil dated to ca. 1100 14C yr B.P. Most of the 74 iron meteorites (0.1–1196 g) recovered have an angular exterior morphology. These meteorites were buried at depths <25 cm and are interpreted to result from fragmentation of the original projectile mass, either at low altitude or during the impact event. Impact of the main mass formed the simple bowl-shaped impact structure associated with an ejecta blanket and crater fill. The increasing availability of LiDAR data for many terrestrial surfaces will serve as a useful tool in the discovery of additional small impact features.
VANCOUVER, British Columbia (Reuters) – Searchers have found the remains of a 10-ton meteor that produced a dramatic fireball in the skies over the Canadian Prairies this month, researchers said on Friday.
Thousands of meteorite fragments have been found densely strewn over a 20-square-kilometre (8 square mile) area south of the community of Lloydminster on the Alberta-Saskatchewan border, according to the University of Calgary.
Searchers have been scrambling to find the remains of the meteor since it streaked across the sky in the early evening of November 20, producing a fire ball that shone brightly enough to be seen over an area 700 km (435 miles) wide.
Investigation of the fireball that lit up the skies of Alberta and Saskatchewan on November 20 has determined that an asteroid fragment weighing approximately 10 tonnes entered the Earth’s atmosphere over the prairie provinces last Thursday evening. And University of Calgary researcher Alan Hildebrand has outlined a region in western Saskatchewan where chunks of the desk-sized space rock are expected to be found.
The fireball first appeared approximately 80 kilometres above and just east of the border city of Lloydminster, Alberta/Saskatchewan, and traveled SSE towards the Battle River valley fragmenting spectacularly in a series of explosions. The fireball penetrated the atmosphere at a steep angle of approximately 60 degrees from the horizontal and lasted about five seconds from 17:26:40 to 17:26:45 MST with the largest explosion at 17:26:44. The fireball was recorded on all-sky and security cameras scattered across Saskatchewan and Alberta in addition to being witnessed by tens of thousands of people who saw it streak across the sky, saw its arc- welding blue flash, or heard the subsequent explosions.
Hildebrand estimates that hundreds of meteorites larger than 50 grams could have landed since the rock was large and its entry velocity was lower than average. The object’s speed is calculated to be only roughly 14 km/sec when it entered the atmosphere versus the average of around 20 km/sec.
Scientist determines pieces of large meteor may have landed in central Sask.
2 days ago
SASKATOON — A leading researcher says one of the largest meteors to streak over Canada in the last decade broke up into pieces that may have landed in central Saskatchewan.
Planetary scientist Alan Hildebrand from the University of Calgary plans to spend the weekend in the Manitou Lake area near the town of Macklin, Sask., about 100 kilometres south of Lloydminster, near the Alberta boundary.
As co-ordinator of the Canadian Fireball Reporting Centre with the Canadian Space Agency, Hildebrand was busy Friday talking with some of the witnesses who sent him 300 e-mail reports about the fireball they saw light up the night sky Thursday.
With their descriptions of the meteor - its brightness, colour and sound - he pinpointed the most likely fall location to be near Manitou Lake.
"Right now, the important thing is not searching because we don't know which field to search in. It's a big world," Hildebrand said. "What's important now is finding proximal eyewitnesses, so you know where meteorites might have fallen."
Meteor sightings have been widely reported across the Prairies, from Edmonton to Regina to Swan River, Man. Witnesses heard sonic boom rumblings and reported it was as bright as the sun.
Cattle farmer Trevor Crisp had just finished hauling a load of animals when he arrived at his home near the village of Richard, about 200 kilometres west of Manitou Lake, for supper Thursday night. It was completely dark outside.
"All of a sudden everything lit up," said Crisp. "I thought it must have been a lightning strike.
"You could hear quite a rumble going through, and you could see a bit of vibration in the windows. It was pretty neat."
Tammy Evans was getting some sleep before her night shift as a nurse in North Battleford, Sask., when her worried 10-year-old daughter ran into the bedroom.
"She said there was a flash of light, and she said the house shook twice and it sounded like dinosaurs were walking."
Minutes later, Evans received a call from her brother-in-law who was driving to Edmonton.
"He said the whole sky lit up, and he had to squint because he couldn't see."
Hildebrand says the meteor could likely be seen up to 700 kilometres away, into the northern United States. It contained about a tenth of a kiloton of energy when it entered the earth's atmosphere, equal to 100 tons of the chemical explosive TNT.
"It would be something like a billion-watt light bulb."
Besides sonic boom sounds, he said witnesses also reported hearing hissing or crackling noises like frying bacon. Fireballs can act as radio transmitters, Hildebrand said, causing odd sounds.
He said other people saw the meteor break into pieces and turn red as it slowed down.
Because it came down over the bald prairie instead of ocean or forest, there's a good chance meteorites may be found, said Hildebrand. He just wants to get to them before they're covered or ruined by more snow.
Martin Beech, an associate professor of astronomy at the University of Regina, said meteorites are valuable to learning about the history of the solar system. The artifacts are 4.5 billion years old.
"Picking up a meteorite is almost equivalent to doing a space exploration mission between Mars and Jupiter," he said.
Richard Herd is curator of Canada's national meteorite collection in Ottawa, with samples from 1,100 different meteorites that have landed across the country.
He said the biggest meteorite fall occurred northeast of Edmonton near the town of Bruderheim in 1960. More than 700 fragments recovered totalled 300 kilograms.
About 75 fireball events are reported each year.
Rick Huziak, an amateur astronomer in Saskatoon, helps operate a fireball camera on top of the University of Saskatchewan physics building that captured video of the meteor.
Although the camera records one every two to three weeks, this meteor was among the brightest seen in Canada in the last dozen years, he said.
"It was quite spectacular. The ground lights up all over the place."
Huziak said only one in a thousand fireballs actually drop meteorites. Most meteors burn up completely.
Phil Langill, director of the Rothney Astrophysical Observatory at the University of Calgary, said he wasn't lucky enough to see the meteor.
But if someone is lucky enough to find one of its meteorites, they should be careful not to contaminate it.
"So if anybody finds it, they should pick it up carefully with a Ziploc bag or something like that and not touch it with their hands."
Figure 1a. The terminal trajectory for Earth impacting asteroid 2008 TC3. The view is looking down on the ecliptic plane.
Figure 1b. The terminal trajectory for Earth impacting asteroid 2008 TC3. The view is from the sun. Note that the asteroid enters Earth shadow at about 1:49 UT so that the final portion of the trajectory is behind the Earth.
Figure 2. The predicted path of the asteroid is noted at 10 km intervals from 100 to 0 km altitude, neglecting atmospheric drag. The red dots indicate the reported instances of atmospheric entry at 65.4 km altitude and for the airburst at 37 km.
Figure 3,. Dispersion of 900 variant orbits, all of which could fit the existing observational data, at an altitude of 50 km. The nominal (most likely) position is denoted by the red dot in the center of the diagram. The results of this Monte Carlo simulation demonstrate that most possible orbits fell within 1 km from the mean, which is at (31.804°E, 20.858°N). The 1-, 2- and 3-sigma uncertainty ellipses are noted in red. Statistically and respectively, these ellipses capture 39%, 86% and 99% of the cases. The time of impact uncertainty at a given altitude is 0.16 seconds, 1-sigma.
Figure 4. Meteosat 8 / EUMETSAT infrared image of the 2008 TC3 explosion. The scale at the right gives the image intensity. Copyright 2008 EUMETSAT
From JPL, update on 2008 TC3:
Summary
A spectacular fireball lit up the predawn sky above Northern Sudan on October 7, 2008. This explosion was caused by the atmospheric entry of a small near-Earth asteroid, estimated to be no more than a few meters in diameter. The explosion likely scattered small meteorite fragments across the Nubian desert below. Although such small impact events occur several times per year around the globe, this case was unprecedented because the asteroid was actually discovered the day before it reached the Earth and the impact location and time were for the first time predicted in advance.
At 6:39 UT (UT = GMT) on the morning of October 6, 2008, Richard Kowalski, at the Catalina Sky Survey, discovered this small near-Earth asteroid using the Mt. Lemmon 1.5 meter aperture telescope near Tucson, Arizona. When the discovery observations were reported to the Minor Planet Center (MPC) in Cambridge Massachusetts, a preliminary orbit computation immediately indicated that the object was headed for an Earth impact within 21 hours. The MPC quickly made the discovery and subsequent "follow-up" observations available to the astronomical community and contacted the NASA/JPL Near-Earth Object Program Office. The MPC also notified NASA Headquarters of the impending impact so that subsequent US government interagency alerts and inter-governmental notifications could begin. By the time this object (now designated as 2008 TC3) entered the Earth's shadow 19 hours after discovery, some 570 astrometric (positional) measurements had been reported from 26 observatories around the world, both professional and amateur.
Within an hour of receiving the initial data set, JPL predicted that the object would enter the Earth's atmosphere above northern Sudan around 02:46 UT on October 7. As the day progressed and more and more data arrived from the MPC, JPL continued to improve the orbit for 2008 TC3 and forwarded updated predictions to NASA Headquarters. On the afternoon of Oct 6th, NASA Headquarters alerted officials at the National Security Council, the Office of Science and Technology Policy, the Department of State, and the Department of Defense Northern Command and Joint Space Operations Center. NASA also issued a press release at approximately 21:30 UT announcing the predicted impact later that night.
Detections of the actual atmospheric impact event suggested that it was an airburst explosion at an altitude of 37 km with an energy equivalent to about one kiloton of TNT explosives. The time and place of the predicted impact agree very well with a number of atmospheric entry observations including those from U.S. government satellites, infrasound signals from at least one ground station, images from the Meteosat 8 weather satellite and a sighting by a KLM airline pilot flying over Chad. The latest JPL trajectory estimate, which carefully considers all available data, including some measurements not available until after the event, is accurate to within a few kilometers at the time of atmospheric entry.
This dramatic prediction of an actual impact underscored the successful evolution of the Near-Earth Object (NEO) Program's discovery and orbit prediction process. The discovery was made, observations were provided by 26 international observatories, the orbit and impact computations were determined, verified and announced well before the impact, which took place only 20.5 hours after the discovery itself. While improvements to the impact prediction process still need to be made, the system worked well for the first predicted impact by a near-Earth object.
Asteroid 2008 TC3 Strikes Earth: Predictions and Observations Agree Steve Chesley, Paul Chodas, and Don Yeomans November 4, 2008
The long-lasting persistent train after the impact of 2008 TC3 over the Sudanese skies (NASA)
From Universe Today Post...
A month after asteroid 2008 TC3 hit the Earth's atmosphere, the first ground-based image of the event has surfaced on the Internet. Admittedly, it's not the fireball everyone has been waiting to see, but it is visual evidence that something hit us above Sudan on October 7th. The image above was taken from a frame of video that was being recorded by Mr. Mohamed Elhassan Abdelatif Mahir in the dawn following the asteroid impact with the atmosphere. The smoky feature is the remnant of the fireball as the 3 meter-wide asteroid blasted through the upper atmosphere, eventually exploding. The long-lasting persistent train is seen hanging in the air, high altitude winds causing it to twist in the morning sunlight.
We may not have a dazzling fireball re-entry video of 2008 TC3, but this striking image provides the first ground-based evidence of the direct hit, and may help refine the search for any meteorites from the disintegrated asteroid…
Although details are sketchy, it would appear that a person on the ground observed the skies of Sudan shortly after 2008 TC3 exploded in the upper atmosphere. It is unclear whether the observer was part of a meteorite-hunting team, or a Sudanese resident videoing the scene, but it is very fortunate he captured this footage. Dr. Muawia H. Shaddad of the University of Karthoum communicated this single frame, and the picture is being showcased as the November 8th NASA Astronomy Picture of the Day.
It is currently the only ground-based evidence that something hit the Earth at the right time and right location as predicted by scientists using the Mount Lemmon telescope in Arizona as part of the NASA-funded Catalina Sky Survey for near-Earth objects. However, as Nancy reported on October 13th, indirect support for an atmospheric fireball came from a webcam on a beach in Egypt. Also, at 02:43 UTC on that Tuesday morning, an infrasound array in Kenya detected an explosion in the atmosphere (with an energy equivalent of 1.1–2.1 kT of TNT). These observations were backed up by the European weather satellite METEOSAT-8, capturing the fireball from orbit. The pilot of a KLM airliner also witnessed a bright flash, 750 miles from the impact location.
This was the first time that an asteroid has been discovered before it hit the Earth, thereby proving an early-warning system for future asteroid impacts is possible. Although there are 5-10 space rock collision events per year, this is the first time we knew something about it before it happened. This is an amazing achievement as 2008 TC3 was only 3 meters in diameter.
Information on National Academies study entitled: "Review of Near-Earth Object Surveys and Hazard Mitigation Strategies." They will be having a meeting from December 9-11, 2008 in Washington, D.C.
Here is more information on the project:
Project Scope
Background In response to long-standing interest in the hazards posed by Near-Earth Objects (NEOs), NASA was directed by Congress in 2005 to initiate a program to detect, track, catalogue, and characterize 90 percent of the objects in space larger than 140 meters in diameter, with a perihelion distance of less than 1.3 astronomical units. As the first step in the definition of this program, NASA was required to prepare and deliver to Congress a report containing an analysis of possible alternative approaches to conducting the requested survey, and an assessment of possible alternatives that could be employed to divert a NEO on a likely collision course with Earth. In response to these instructions, NASA undertook a series of activities culminating in the publication in March 2007 of Near-Earth Object Survey and Deflection Analysis of Alternatives: Report to Congress and 2006 Near-Earth Object Survey and Detection Study.
In response to these documents, Congress included language in the Joint Explanatory Statement attached to the Consolidated Appropriations Act 2008 calling on NASA to contract with the National Research Council to undertake a two-phase study to review those two NASA studies and other relevant literature, and to provide recommendations focusing on both the optimal approach to surveying the NEO population and the optimal approaches to developing a deflection capability.
Statement of Task The National Research Council Space Studies Board, in cooperation with the Aeronautics and Space Engineering Board, shall conduct a two-part study to address issues in the detection of potentially hazardous NEOs and approaches to mitigating identified hazards. Both tasks should include an assessment of the costs of various alternatives, using independent cost estimating. Options that blend the use of different facilities (ground- or space-based), or involve international cooperation, may be considered. Each study phase will result in a report to be delivered on the schedule provided in the contract. Key questions to be addressed during each phase of the study are the following:
Task 1: NEO Surveys What is the optimal approach to completing the NEO census called for in the George E. Brown, Jr. Near-Earth Object Survey section of the 2005 NASA Authorization Act to detect, track, catalogue and characterize the physical characteristics of at least 90% of potentially hazardous NEOs larger than 140 meters in diameter by the end of year 2020? Specific issues to be considered include, but are not limited to, the following: --What observational, data-reduction, and data-analysis resources are necessary to achieve the Congressional mandate of detecting, tracking, and cataloguing the NEO population of interest? --What physical characteristics of individual objects above and beyond the determination of accurate orbits should be obtained during the survey to support mitigation efforts? --What role could be played by the National Science Foundation's Arecibo Observatory in characterizing these objects? --What are possible roles of other ground- and space-based facilities in addressing survey goals, e.g., potential contributions of the Large Synoptic Survey Telescope (LSST) and the Panoramic Survey Telescope and Rapid Response System (Pan STARRS)?
Task 2: NEO Hazard Mitigation What is the optimal approach to developing a deflection capability, including options with a significant international component? Issues to be considered include, but are not limited to, the following: --What mitigation strategy should be followed if a potentially hazardous NEO is identified? --What are the relative merits and costs of various deflection scenarios that have been proposed?
This project is sponsored by NASA. The start date for this project is November 4, 2008.
Schedule: An interim report, based upon Task 1, shall be produced and delivered to NASA by September 30, 2009. A final report including both Tasks 1 and 2 will be delivered by December 31, 2009.
From ESA, regarding student involvement in the upcoming IAA Planetary Defense Conference:
ESA is holding a competition for the upcoming Planetary Defense Conference in 2009, in order to stimulate some innovative research and encourage European research students to participate. The Advanced Concepts Team (ACT) has come up with a few concepts that young researchers from various fields may wish to research. The titles of the different concepts are:
* Deflecting Binary asteroid systems * Graveyard orbit deflection * Maximum charge of a satellite * Deflection strategies using multiple spacecraft * Avoiding reaggregation by electrostatic charge * The Magnetostatic Tractor * Lorentz Deflection during an Earth fly-by * Observing Apophis with LISA * Changing the internal structure of asteroids
To see details of these concepts, or for more information on how to take part, visit our webpage:
Abstracts must be submitted before _1 December 2008.
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