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.

25 June 2009

Shuttle Plumes Aid in Confirming Comet Explosion at Tunguska in 1908

Noctilucent clouds observed from Donnelley Dome near Fairbanks, Alaska, resulting from a post-space shuttle plume in August 2007 (Credit: M.J. Taylor and C.D. Burton/Utah State University).

Kelley, M. C., C. E. Seyler, and M. F. Larsen (2009), Two-dimensional turbulence, space shuttle plume transport in the thermosphere, and a possible relation to the Great Siberian Impact Event, Geophys. Res. Lett., doi:10.1029/2009GL038362, in press (accepted 22 June 2009).

From the article in Universe Today:

The 1908 Tunguska event has always been mysterious and intriguing because no one has been able to fully explain the explosion that leveled 830 square miles of Siberian forest. But the latest research has concluded that the Tunguska explosion was almost certainly caused by a comet entering the Earth’s atmosphere. And how researcher Michael Kelly from Cornell University came to that conclusion it quite interesting: He analyzed the space shuttle's exhaust plume and noctilucent clouds.

“It’s almost like putting together a 100-year-old murder mystery,” said Kelley, a professor of Engineering, who led the research team. “The evidence is pretty strong that the Earth was hit by a comet in 1908.” Previous speculation had ranged from comets to meteors.

Noctilucent clouds are brilliant, night-visible clouds made of ice particles and only form at very high altitudes and in extremely cold temperatures. These clouds appeared a day after the Tunguska explosion and also appear following a shuttle mission.

The researchers contend that the massive amount of water vapor spewed into the atmosphere by the 1908 comet’s icy nucleus was caught up in swirling eddies with tremendous energy by a process called two-dimensional turbulence, which explains why the noctilucent clouds formed a day later many thousands of miles away.
Noctilucent clouds over Saimaa. Credit: Wikipedia

Noctilucent clouds are the Earth’s highest clouds, forming naturally in the mesosphere at about 55 miles over the polar regions during the summer months when the mesosphere is around minus 180 degrees Fahrenheit (minus 117 degrees Celsius).

The space shuttle exhaust plume, the researchers say, resembled the comet’s action. A single space shuttle flight injects 300 metric tons of water vapor into the Earth’s thermosphere, and the water particles have been found to travel to the Arctic and Antarctic regions, where they form the clouds after settling into the mesosphere.

Kelley and collaborators saw the noctilucent cloud phenomenon days after the space shuttle Endeavour (STS-118) launched on Aug. 8, 2007. Similar cloud formations had been observed following launches in 1997 and 2003.

Following the Tunguska Event, the night skies shone brightly for several days across Europe, particularly Great Britain — more than 3,000 miles away. Kelley said he became intrigued by the historical eyewitness accounts of the aftermath, and concluded that the bright skies must have been the result of noctilucent clouds. The comet would have started to break up at about the same altitude as the release of the exhaust plume from the space shuttle following launch. In both cases, water vapor was injected into the atmosphere.
The scientists have attempted to answer how this water vapor traveled so far without scattering and diffusing, as conventional physics would predict.

“There is a mean transport of this material for tens of thousands of kilometers in a very short time, and there is no model that predicts that,” Kelley said. “It’s totally new and unexpected physics.”

This “new” physics, the researchers contend, is tied up in counter-rotating eddies with extreme energy. Once the water vapor got caught up in these eddies, the water traveled very quickly — close to 300 feet per second.

Scientists have long tried to study the wind structure in these upper regions of the atmosphere, which is difficult to do by such traditional means as sounding rockets, balloon launches and satellites, explained Charlie Seyler, Cornell professor of electrical engineering and paper co-author.

“Our observations show that current understanding of the mesosphere-lower thermosphere region is quite poor,” Seyler said. The thermosphere is the layer of the atmosphere above the mesosphere.

"1908 Tunguska Event Caused by Comet, New Research Reveals"
24 June 2009
Nancy Atkinson
Universe Today

Link: Article from Universe Today

"Tunguska impact riddle solved at last"
24 June 2009
SkyMania News

Link: Article from SkyMania

Link: Paper: Two-dimensional turbulence, space shuttle plume transport in the thermosphere, and a possible relation to the Great Siberian Impact Event

Link: Cornell University News Release

23 June 2009

New Fact Sheet from the Secure World Foundation on NEOs

There is a new fact sheet from the Secure World Foundation (SWF) on NEOs. Perhaps a good primer for those interested.

Link: Fact Sheet from SWF (PDF)

Link: News Announcement from SWF on NEOs

New Spaceguard Telescope in the UK

UK Spaceguard Centre

From the article...

A telescope worth £500,000 which will monitor the threat posed by asteroids to earth is being delivered to an observatory in Powys.

The Spaceguard Centre, in Knighton, has been given the Schmidt camera free of charge by the Institute of Astronomy at Cambridge University.

It will be used to spot near earth objects and then track them.

The telescope is not used in Cambridge anymore because of light pollution, but Powys' dark skies are said to be ideal.

The telescope is expected to arrive in Knighton later on Friday, but it could be months before it is installed.

It will be stored temporarily at a water bottling plant in the town.

The Spaceguard Centre started a campaign to raise £54,000 to install the Schmidt camera in January 2008.

The large telescope has a wide field of view and takes photographs of the sky.

A spokeswoman for the Spaceguard centre said the Schmidt camera was 40 years old and was worth about £500,000.

She described it as a "phenomenal piece of British engineering".

It is thought the telescope will work well in Knighton because the sky above the town is free, in the main, from light pollution.

Jay Tate, who runs the centre, has said previously: "Nasa searches for near earth objects and it funds six telescopes in the US and two in Italy and Australia, but no-one else is doing this sort of work in the UK.

"(The telescope) would mean we could search for objects as well as tracking them once they have been identified."

The Spaceguard Centre currently has a robotic telescope, which is able to track asteroids and its observatory attracts school parties and tourists.

Link: BBC Article

18 June 2009

NEO News (06/18/09) Summer Stories

From Dave Morrison.

NEO News (06/18/09) Summer Stories

This edition of NEO news is devoted to several current stories that are creating some press and public interest. Some are serious, others are just summer madness. In any case, it is perhaps useful that we be aware of these issues.

David Morrison


As first discussed a week ago in an article by Leonard David on, there is a move to stop releasing the routine observations of large fireballs that have been made by U.S. surveillance satellites. Peter Brown at University of Western Ontario and others have made good use of these data to define the impact frequency for objects in the meter size range and to help locate meteorite falls such as Tagish Lake. This is a serious issue, although some news sources are greatly exaggerating by claiming that the absence of global fireball data somehow increases public risk from impacts. Unfortunately, this topic feeds those who are already paranoid about government secrecy. Following is a sober summary of the issues from Nature on-line:

Satellite information on incoming meteors is blocked.
Geoff Brumfiel, Nature, 12 June 2009

The US military has abruptly ended an informal arrangement that allowed scientists access to data on incoming meteors from classified surveillance satellites. The change is a blow to the astronomers and planetary scientists who used the information to track space rocks, especially those that burn up over the oceans or in other remote locations. "These systems are extremely useful," says Peter Brown, an astronomer at the University of Western Ontario in London, Canada. "I think the scientific community benefited enormously."

When the policy changed is unclear. The website reported the end of the relationship on 10 June, but Brown says that he was told at the beginning of this year that there would be no further data releases. Mark Boslough, a physicist at Sandia National Laboratories in Albuquerque, New Mexico, says he was told this spring that he could no longer publicly discuss the classified data to which he had some access. Neither scientist could give a reason for the end of the arrangement, and the United States Air Force, which operates the satellites, did not respond in time for Nature's deadline. The Air Force did issue a 16 March memo on the military classification of fireball data, but Nature could not confirm its contents.

The Defense Support Program satellite network is part of the Pentagon's early-warning system. Since 1970, 23 infrared satellites in the series have been launched into geosynchronous orbit to monitor the globe for missile launches or atmospheric nuclear blasts.

But the same infrared sensors were perfect for spotting fireballs as they streaked across the atmosphere, according to Brian Weeden, a former Air Force captain who now works at the Secure World Foundation, a non-profit organization based in Superior, Colorado. The satellites could precisely detect the time, position, altitude and brightness of meteors as they entered Earth's atmosphere. Weeden, who left the Air Force in 2007, says that the military didn't consider that information particularly useful, or classified. "It was being dropped on the floor," he says.

Under an informal arrangement, at least some of the data seem to have been provided on an ad-hoc basis to scientists studying meteorites. Often it came in the form of an anonymous, tersely worded e-mail describing the coordinates, altitude and size of a fireball. Brown, who has collected the data since 1994, declined to specify who sent the reports.

Even the short descriptions of events were enormously helpful. In 2002, Brown and his colleagues used a larger data set from the satellites to quantify the number of objects striking Earth each year (P. Brown et al. Nature 420, 294-296; 2002). Last year, they were used to narrow the search for remnants of the asteroid 2008 TC3 in the Sahara Desert in North Africa, and they were also crucial in recovering a meteorite fragment in 2000 from Tagish Lake in northern Canada. "In both of those cases it's hard to say whether this would have been picked up without the satellite data," Boslough says.

The data also provide a useful check against ground-based instruments monitoring low-frequency sound waves and dust from the fireball explosions, says Brown.

Brown says that whatever the reason, the end of the relationship has left the tight-knit meteorite community smarting. The global reach of the satellites and the data they supplied were unparalleled, he says. "There's nothing else that even comes close," he says.



There has been considerable Internet chatter about a claim that a 14-year-old boy in Essen, Germany, was knocked off his bicycle by a small meteorite. There were no other witnesses, but his story was apparently believed at least locally in Germany, and it has spread widely. The "facts" as reported are almost entirely wrong. However, we do not know what actually happened, or whether the implausible accounts come from the boy or local reporters. Much of the following information is from the Discover-Badastronomy website of Phil Plait (

The original English-language story is from the Telegraph in UK ( They wrote:

Gerrit Blank, 14, was on his way to school when he saw "ball of light" heading straight towards him from the sky. A red hot, pea-sized piece of rock then hit his hand before bouncing off and causing a foot wide crater in the ground. The teenager survived the strike, the chances of which are just 1 in a million - but with a nasty three-inch long scar on his hand.

He said: "At first I just saw a large ball of light, and then I suddenly felt a pain in my hand. Then a split second after that there was an enormous bang like a crash of thunder. The noise that came after the flash of light was so loud that my ears were ringing for hours afterwards. When it hit me it knocked me flying and then was still going fast enough to bury itself into the road," he explained.

Scientists are now studying the pea-sized meteorite which crashed to Earth in Essen, Germany. Chemical tests on the rock have proved it had fallen from space. Ansgar Kortem, director of Germany's Walter Hohmann Observatory, said: "It's a real meteorite, therefore it is very valuable to collectors and scientists."
What are we to make of this? Most of the "facts" don't bear close examination. The "meteorite" is pea sized and looks like a small piece of gravel. If it is a meteorite, it must have been the product of the explosion/disintegration of a larger meteor many kilometers high (since small meteorites can't make it through the atmosphere). It would have reached the ground at terminal velocity (which is low for a pea-size rock) several minutes after the high-altitude explosion. Such a small stone could not make a crater or do any damage to a paved street. It would also have been cool (it would quickly equilibrate with the air it was falling through). Compare this with the story reported in the newspapers:

Speed 30,000 mph - impossible (unless they mean the entry speed)
Red-hot - impossible
Brilliant fireball coming straight toward the boy - impossible
Loud sound at time it hit - impossible
Burned hand - not from the meteorite
Crater in road - not supported by photos

The question of whether this was a real meteorite apparently is also open. A writer to the badastronomy blog wrote: "I just checked the German sites reporting this. Ansgar Korte is quoted as saying “Ist es tatsächlich ein echter Meteorit, dann hat das Exemplar sogar einen gewissen Wert für Sammler und Mineralogen." That would correctly be translated to "IF it is a real meteorite, it would have a certain value for collectors and mineralogists." In any case, a pea-sized meteorite is easily purchased (and inexpensive) if someone wanted to fabricate a hoax.
I have no clue where the fault is, but I recommend skepticism in accepting this story as evidence of a person being hit directly by a meteorite.

David Morrison



Rusty Schweickart reports the following note from the AAAS public policy blog, quoting from the recent U.S. House Appropriations bill providing FY10 funding for NASA:

Near Earth object observations -- The recommendation includes $5,800,000 for near Earth object observations, an increase of $2,000,000 to support ongoing scientific research at the Arecibo Observatory in the fields of climate change and space weather...

The fact that this item is listed under NEOs suggests that the members of Congress may intend this as operating support for the Arecibo planetary radar, which has been so valuable in studying both the orbits and the physical characteristics of NEOs. However, the underlying issue of the continued operations of the entire Arecibo Observatory, which is managed and funded by the National Science Foundation, does not seem to be addressed in this section of the Appropriations bill.

Stay tuned Š.



An ABC-TV mini-series called "Impact" will be broadcast in the U.S. on June 21. You will find the trailer and some comments on the Badastronomy website at (

The movie plot seems to be that a giant meteor storm hits the Moon, excavating huge rocks (bigger than mountains) that rain down on Earth. Then comes the bad part. The meteors contained a "piece of a brown dwarf" which is embedded in the Moon and has increased its mass to twice the mass of the Earth (perhaps they were thinking of a white dwarf, which is extremely dense, not a brown dwarf). Apparently this produced an increase in gravitational mass but not inertial mass (another miracle of nature) because the Moon is now headed for a collision with the Earth. If you care about the outcome, you will need to watch the film.


Stories about the fictional planet Nibiru and its collision with Earth in December 2012 have blossomed on the Internet. Claims about a 2012 doomsday are the theme of a new from Columbia Pictures titled "2012", to be released in November 2009. Apparently cosmic impacts are a part of the plot.

The film's trailer, appearing in theaters and on their website, shows a tidal wave breaking over the Himalayas, with only the following words: "How would the governments of our planet prepare 6 billion people for the end of the world? [long pause] They wouldn't. [long pause] Find out the Truth. Google search 2012".

The film publicity includes creation of a faux scientific website ( for "The Institute for Human Continuity", which is entirely fictitious. According to this website, the IHC is dedicated to scientific research and public preparedness. Its mission is the survival of mankind. The website explains that the Institute was founded 1978, and in 2004 IHC scientists confirmed with 94% certainty that the world would be destroyed in 2012. This website encourages people to register for a lottery to select those who will be saved. I learned from Wikipedia that this sort of fake website is a new advertising technique called "Viral Marketing", by analogy with computer viruses.
For lots more information on the Nibiru and 2012 hoaxes see ( For the film, we will have to wait until late November.


NEO News (now in its fourteenth year of distribution) is an informal compilation of news and opinion dealing with Near Earth Objects (NEOs) and their impacts. These opinions are the responsibility of the individual authors and do not represent the positions of NASA, Ames Research Center, the International Astronomical Union, or any other organization. To subscribe (or unsubscribe) contact For additional information, please see the website If anyone wishes to copy or redistribute original material from these notes, fully or in part, please include this disclaimer.

05 June 2009

NEO News (06/04/09) Planetary Defense at Granada pt 2

From Dave Morrison.

NEO News (06/04/09) Planetary Defense at Granada pt 2

The edition of NEO News is a continuation of my last message, which was sent 05/29/09.The focus here is on international political support, as well as technical issues associated with protecting our planet from asteroid impacts. A future message will summarize the conclusions and recommendations from the conference.

David Morrison



The International Academy of Astronautics was the primary sponsor of this planetary defense conference, which was held April 27-30 in Granada, Spain. Jean-Michel Contant welcomed the attendees on behalf of the IAA and committed the organization to support future Planetary Defense Conferences at two-year intervals. The next meeting will be in Bucharest, Romania, on May 9-14, 2011.

The IAA has recently completed its own study of the impact threat, summarized at this meeting by Ivan Bekey, called "Dealing with the Threat to Earth from Asteroids and Comets" (2009, 140 pages). The abstract of this document says "The Earth has been struck by asteroids and comets many times throughout its history. This report of the International Academy of Astronautics addresses the nature of the threat, expected future impacts, and the consequences of impacts from various size NEOs. It reviews current programs to detect, track, and characterize NEOs, and the future improvements required in order to take responsible and timely action. It identifies a number of techniques that could alter an incoming NEO's orbit so as to avoid an impact. It addresses the organizational aspects that will have to be dealt with if a serious international capability is to be developed and employed to mitigate the threat. It then addresses behavioral factors and the sociological and psychological aspects of the threat and attempts at its mitigation before, during, and after an intercept attempt, whether successful or not. Lastly the report examines some of the principal international policy implications that must be dealt with if the world is to act in a timely, unified, and effective way with the very real threat due to NEOs." To access full text go to this website: The report contains useful information, but since it was 4 years in preparation, parts of it are rather dated.

D. Koschny of ESA (the European Space Agency) reported on an initiative to include asteroid impacts within the European Space Situational Awareness Programme. Situational awareness is concerned with perception of the environment critical to decision-makers in complex, dynamic areas such as aviation, air traffic control, and military command and control. The objective of the European Space Situational Awareness initiative is to support the European independent utilization of and access to space for research or services, through providing timely and quality data, information, services and knowledge regarding the environment, the threats, and the sustainable exploitation of the outer space. The components of this initiative are space surveillance, space weather, and NEOs. For NEOs, they intend to study tracking, orbit determination, orbital databases, and identification of impact risks. The main objective is to issue impact warnings. They intend to provide information on the impact probability and/or miss distance of NEOs. To do this, they will assess impact analyses and perform their own risk assessments.
As these are all tasks that are already being addressed by the NASA NEO Program, the initial ESA activity may be to transmit this information to European decision-makers. No independent European detection or orbital analysis plans were suggested.

Rusty Schweickart provided an update to this meeting on the "Call for Global Response" of the international panel on Asteroid Threat Mitigation of the Association of Space Explorers (made up of astronauts and cosmonauts who have flown in space). Their report has been submitted to the UN committee on the Peaceful uses of Outer Space (COPUOS) and is currently entering a process of deliberation and potential action within the UN. We will be reporting on it in the future.


Mike A'Hearn of the University of Maryland summarized the current study of the NEO Hazard being carried out by the National Research Council of the National Academy of Sciences. This study, chaired by Irwin Shapiro, the Director emeritus of the Harvard College Observatory, is primarily addressing requests from Congress. They are considering the challenge of surveying potentially hazardous NEAs at smaller sizes, to reach 90% completeness at a diameter of 140 m. They are also considering a wide variety of techniques for characterization and mitigation. Congressional staff members have told the NAS-NRC steering committee that the Congress is interested in understanding how international collaboration should work in this area. This NRC study and recommendations should be completed at the end of 2009.

The capabilities of two large ground-based survey projects were
discussed: Pan-STARRS presented by M. Granvik (with the first of four survey telescopes near completion in Hawaii, funded by the U.S. Air Force), and LSST presented by Z. Ivezic (a single wide-field 8-m telescope to be constructed in Chile, with detailed studies underway supported by the U.S. National Science Foundation and the U.S.
Department of Energy). Space-based asteroid detection in the thermal infrared was discussed by Amy Mainzer of JPL, who described the capabilities of WISE (the NASA Widefield Infrared Survey Explorer), which is to be launched in November 2009, and of a possible dedicated infrared NEA survey called NEO-CAM to follow.

Peter Garretson (Lt. Col., US Air Force) reported the results of a scripted multi-agency deflection and disaster exercise. Participants included middle-level representatives of U.S. Air Force, NASA, National Security Council, Department of Defense, Department of State, Department of Homeland Security, Navy, Coast Guard, Federal Emergency Management Agency, and Defense Threat Reduction Agency. The objective was to better understand how responsible government organs would respond in the absence of clear policy on roles and missions.
The table-top simulation involved two specific threats: a binary asteroid the size of Apophis targeted in the Atlantic Ocean off the coast of Nigeria, and a 50-m metallic asteroid targeted on the Eastern U.S. near Washington DC. They studied possible mitigation of the ocean impact given 7 years warning, and disaster management for the U.S. impact given 72 hours warning. The participants were aware of lack of previous planning. While a number of useful analogs exist, as well as procedures that could be used or adapted, attempts or do so in the moment are likely to be much less successful than advance preparation. Participants recommended that the NEO scenario should be elevated to higher levels with more senior players. They also concluded that proper planning and response to a NEO emergency requires delineation of organizational responsibilities including lead agency and notification standards, but they were not able to agree on which should be the lead agency. This was the first time such a multi-agency exercise had taken place in the U.S. Dealing with similar issues on an international scale would be even more problematic.


Lance Benner (JPL) provided an update on the always-spectacular discoveries using the Arecibo and Goldstone radars, which are our most powerful tools for both orbital and physical characterization of NEAs (if they come with radar range). He showed an interesting comparison between the radar and spacecraft images of Itokawa; the radar got the size and shape right but could not resolve the fine detail, including the many boulders on the surface. Among the newly imaged objects were 1992 UY4, 1998 CS1, and the binary NEA 2000 DP107. Radar data indicate that about 10% of NEAs are actually contact binaries, and he stressed how different NEAs are, with "no such thing as a typical NEA."

Rick Binzel (MIT) reviewed telescopic data on the physical properties of NEAs. Large telescopes are being used to obtain visible and near-infrared colors, spectrophotometry, and polarimetry. He introduced a more accurate classification of 42-channel spectrophotometry to create what he calls the Bus-DeMeo taxonomy, with more than 20 classes. Reminding the audience that we have thousands of direct samples of NEAs in the form of meteorites, Binzel noted that one of the objectives of telescopic studies is to link the remote measurements of NEA spectra with specific meteorite types. He used such an analysis to conclude that Apophis has the surface composition of a LL Chondrite. If this is correct, we can use lab study of meteorites to estimate that Apophis is composed primarily of olivine and pyroxene with relatively low metal content. The bulk density of this material is 3.2 g/cc. Similar telescopic data for
2008 TC3 can be calibrated from the recovered meteorites. Binzel called this classification of NEAs from telescopic data "our first line of defense against NEOs."

The use of small spacecraft for detailed physical characterization of NEAs was the subject of several presentations and poster papers. The Japanese Hayabusa mission to Itokawa is an outstanding example of this approach. David Morrison stressed that flybys are of little use for small NEA targets, with a rendezvous required to determine such key properties as mass, density, and surface topography. He described a low-cost mission called MAAT that has been studied at NASA Ames Research Center. Another paper described the Didymos explorer mission designed to explore a binary NEA. Another proposed Apophis mission called Foresight is intended to tag Apophis with a radio transponder for very precise orbit determination, and PROBA-IP is an ESA technology demonstration mission targeted to Apophis. There was considerable discussion of the great value of a combined rendezvous and ballistic impact mission. Such a mission called Don Quijote was studied by ESA but now seems to have been dropped. However, ESA is working with Japan on an alternative NEA rendezvous mission without the impactor.


This was an excellent meeting: well attended and with some fine technical and policy papers presented. Most of the leaders in the NEO defense arena were present, as well as many new participants, especially many young scientists from Europe.

Several speakers assumed that the current estimates of the impact rate are greater than previously thought, adding urgency to this threat. Judging by some of the presentations at this meeting, these assessments were based on faulty or misinterpreted data. As Al Harris (Space Science Institute) showed (discussed in NEO News 05/29/09), at least 90% of the risk associated with impact by an unknown asteroid has been eliminated by the Spaceguard Survey, and in addition the NEO population data summarized by Harris indicate fewer sub-km asteroids by at least a factor of 2, relative to previous power-law estimates.
It is curious to see claims by policy analysts that the impact threat is increasing while the scientific community comes to the opposite conclusion.

There was thus a certain unreality about some of the discussions.
Many international and European organizations are becoming concerned about the impact hazard just at the time it is being rapidly reduced by the Spaceguard Survey. While there have been some excellent paper studies (for example, the U.K. impact hazard study in 2001), so far only two nations have made significant contributions to actually mitigating the impact hazard: the United States and Japan. The U.S.
has financed the Spaceguard survey, the Minor Planet Center, the NEO Program Office at JPL, the planetary radar systems at Arecibo and Goldstone, studies of the next generation of survey telescopes (including construction of the Pan-STARRS-1, casting the 8-m mirror for the LSST, building the WISE infrared survey satellite, and sending the NEAR-Shoemaker mission which orbited and landed on Eros).
Japan has carried out the only spacecraft study of a sub-km NEA, Itokawa, including brief landing and collection of a sample now en route back to Earth.

Three surprising new results presented at this meeting stand out in my mind. (1) The strange case of the Carancas meteorite fall on the Altiplano at the Peru-Bolivia border on September 15, 2007, which was described by Tancredi. A stony (ordinary chondrite) meteorite with an original mass of a few tons hit at a few km/s speed and formed a 15-m wide crater. This should not happen according to conventional models.
(2) Boslough's supercomputer simulations of the Tunguska impact indicate that stony objects <40m in diameter can produce highly destructive airbursts, and somewhat larger airbursts can also generate substantial melting of silicates at the surface when their fireball reaches the ground. (3) The unique case of 2008 TC3 showed that even with the current survey systems it is possible to detect a small NEA very close to impact, accurately predict the impact time and place, and recover meteorites. This is also our first chance to directly compare remote sensing observations of the parent object in space with "ground truth" from recovered samples. TC3 has greatly increased interest in detection of small asteroids within a few days of impact.


NEO News (now in its fourteenth year of distribution) is an informal compilation of news and opinion dealing with Near Earth Objects
(NEOs) and their impacts. These opinions are the responsibility of the individual authors and do not represent the positions of NASA, Ames Research Center, the International Astronomical Union, or any other organization. To subscribe (or unsubscribe) contact For additional information, please see the website If anyone wishes to copy or redistribute original material from these notes, fully or in part, please include this disclaimer.
Note: Any opinions expressed on the blog are solely those of the author. The site is not sponsored by, nor does it represent the opinions of, any organization, corporation, or other entity.