From Dave Morrison.
NEO News (07/01/08) Population and impact frequency
This edition of NEO News contains one of our periodic updates on the progress of the Spaceguard survey, a topic that is intertwined with estimates of the population of NEAs as a function of size. As in the past, the most detailed such estimates come from Alan Harris. Reproduced below is his recent article on this subject, published in Nature last week. I have not included any of the graphics (two figures) or the references; for these, please reference the original article in Nature.
All estimates of NEA populations and impact rates are plagued by uncertainties concerning the albedos of NEAs and hence the conversions from the observed quantities (magnitudes) to size and energy. The are also uncertainties in the magnitude scales used by different observing groups. Models include different assumptions, and it is thus difficult to compare detailed numerical results. The results from Harris are internally self-consistent, but other self-consistent models yield slightly different conclusions, even using the same observational data. Harris reports (for early June) that 742 near-Earth asteroids of diameter greater than 1 km have been discovered. He estimated a total of 940, concluding that the Spaceguard Survey has identified about 79% of NEAs larger than 1 km. Lindley Johnson of NASA Headquarters, using the same data, uses the discovery of 744 (as of late June) but adopts a different total population of NEAs >1 km to yield a completeness of 86%. Either way, the Spaceguard Survey has been a great success.
The most important innovation in the Harris models discussed below is in the use of new astronomical data from the surveys to conclude that the size frequency distribution of NEAs is not a straight-line power law (his Figure 1 in the Nature paper). The dip in population of sub-km NEAs results in lower risks, as he discusses below.
In spite of the differences between models, it seems to me that with all the new data from Spaceguard, the population and impact frequency numbers are now pretty solid. But how we interpret them is an individual matter. Some feel that the risk from sub-km NEAs is unacceptable, others that it is negligible. It is in this area of interpretation that we see the strongest divergence of opinion about the magnitude of the remaining NEA impact risk.
David Morrison
======================================
Nature: Vol 453 pg 1178 June 2008
COMMENTARY: WHAT SPACEGUARD DID
by Alan Harris
The sky isn't falling, but there are still good reasons for keeping an eye on it. In 1991, a NASA-sponsored international working group convened to develop a thorough survey of near-Earth objects (NEOs) - predominately asteroids with an orbit that brings them within 1.3 astronomical units of the Sun. The objective of the survey would not be a mere sampling of the large asteroids that might constitute a risk to Earth, but rather a census. The report defined the 'Spaceguard Survey'. Spaceguard's goal was to identify most NEOs larger than 1 kilometre in diameter within a decade. The impact of an asteroid larger than 1 kilometre in diameter has the potential to cause a global climatic perturbation, similar to a 'nuclear winter', and could lead to billions of deaths worldwide. Such events, although less frequent than smaller 'impacts' such as the Tunguska event in Russia (see page 1157), nevertheless present a greater risk of death, even to individuals. Moreover, they carry the additional risk of ending civilization. So, it is clear to most why a survey might be important.
The idea was slow to catch on within NASA, but by May 1998, Carl Pilcher, the Science Director of Solar System Exploration in the NASA Office of Space Science, testified before the Subcommittee on Space and Aeronautics of US Congress that "NASA is committed to achieving the goal of detecting and cataloguing 90% of NEOs larger than 1 kilometre in diameter within ten years". This for many was the formal start of Spaceguard, so it is appropriate, a decade later, to ask whether its goals have been met. The pedantic answer is no, but in terms of risk reduction - or more precisely, knowing whether an impact will, or will not, occur in our lifetimes - Spaceguard identified a fraction of NEOs responsible for more than 90% of the potential impact risk, and found that impacts from that fraction pose a negligible risk in the next 50-100 years. The remaining short-term risk is almost entirely from any remaining undiscovered NEOs. In that sense, the Spaceguard Survey has been a remarkable success.
Two years ago, I was commissioned by NASA, through the NEO Program Office at the Jet Propulsion Laboratory in Pasadena, California, to assess the progress of Spaceguard. I filed my final report with NASA in March 2007 and have presented a brief summary of the main results. It is easy enough to keep count of the number of discovered objects larger than a given size, but to know when 90% have been found, one must estimate the total population. This is a bit of a bootstrap process, using the survey itself to estimate everything out there. In the simplest terms, if we scan the sky tonight, the number of detections of already-known objects compared to the total number of objects detected during a test interval gives us a measure of completeness. In detail, it is not so simple because not all NEOs are equally detectable.
How is Spaceguard doing? As of 10 June 2008, 742 near-Earth asteroids of diameter greater than 1 kilometre had been discovered. In my report I estimated a total of 940, and so the Spaceguard Survey has identified about 79%; not quite 90%, but not bad considering the uncertainties and the efforts required to reach 90%. Meanwhile the estimated risk of impact is dwindling. In the very largest size range, asteroids about 10 kilometres in diameter, the three already discovered are almost certainly all that exist. These would produce an impact similar to that which killed the dinosaurs 65 million years ago, with an estimated impact interval of around 108 years - roughly the last time dinosaurs walked on Earth. Oddly, an object that might cause a Tunguska-like event - roughly 50 metres in diameter - should collide with Earth only about every 1,500 years, and the last event we saw was only 100 years ago.
Recently, Mark Boslough at Sandia National Laboratories, in Albuquerque, New Mexico, suggested that the energy of the Tunguska event may have been as low as 3 megatonnes. That adjustment reduces the expected time between similar events to perhaps about once in 500 years, still leaving the chances of an event within a century as unlikely. 'Statistics of one' cannot be held too rigorously to formal probability estimates, but our view of the skies has produced a strong predictor for the frequency of impacts. It is so strong, in fact, that it could and should rule out some suggestions of past impacts such as the multiple kilometre-sized objects claimed by some to have pelted Earth during the Holocene period. Such an event is inconsistent with what we see in the skies, by about two orders of magnitude.
Another NASA study in 2003, estimated the expected damage from impacts of various sizes. Using those values of expected damage, and the impact frequency from the newly derived population, I estimated the 'risk spectrum' of impacts over the entire size range of those that can penetrate the atmosphere. Figure 2 shows that 'spectrum', first for the entire population, that is, the 'intrinsic risk' before any NEOs had been discovered, and secondly the 'residual risk' from the fraction of the NEO population that remains undiscovered. Since the objects that have been discovered have been found to have no, or a vanishingly small, probability of hitting Earth in the next 50 or more years, we can think of that fraction of the intrinsic risk as 'retired' for the short term over which we can predict impact trajectories, about a human lifetime.
Figure 2 shows that the risk from large impacts -- the kind that would cause global climatic disaster and potentially bring down our civilization - has been dramatically reduced, by more than an order of magnitude. In the smaller size range, from several-hundred-metre-diameter objects that could cause massive tsunamis if they crashed into an ocean, down to sub-hundred-metre objects the size of that in the Tunguska event - which could cause ground damage from airbursts - current surveys have done little to retire the risk. But the intrinsic risk from these events is very small, and in fact resembles that of other natural disasters such as tsunamis, earthquakes and volcanic eruptions in that they do not pose a global threat to life as we know it.
In the 2003 NASA report, the recommendation was made for a new survey to reduce the assessed residual impact risk from objects less than 1 kilometre in diameter by a further order of magnitude. It was estimated at that time that to achieve this goal would require discovering 90% of NEOs larger than 140 metres in diameter. This has become the new mantra of survey plans, but perhaps this should be reconsidered. Because of the steep dip in the population curve in the size range between about 50 metres and about 500 metres, the intrinsic impact frequency, and hence the impact risk, is about three times lower than was estimated in the 2003 report. So, in a way, two-thirds of the risk assumed to exist in those reports is gone already, without even looking at the sky. In the earlier reports, the 'residual risk' to be addressed by a next-generation survey was assumed to be approximately 300 fatalities per year, but using my new population estimate that figure drops to around 80 per year. In comparison to other risks in life, this is negligible.
What is the risk that your death will come from the sky? Before the Spaceguard Survey, it was thought to be comparable to the risk of dying in a commercial aeroplane accident. Currently, however, the residual risk from the remaining undiscovered NEOs is more comparable to the risk of death from a fireworks accident. At some point one has to ask how far down we need to drive the residual risk, especially because the cost of doing so increases steeply as the size of impactors decreases.
Be that as it may, plans are continuing for next-generation surveys and they may serve another purpose. The Large Synoptic Survey Telescope (LSST), a ground-based, wide-field instrument with an 8.4 metre aperture, is planned to enter service by about 2012. Recognizing the diminishing value of driving our assessement of the impact risk so low, the LSST project has adopted the NEO survey as only one of many scientific goals for the telescope, and in particular has emphasized the scientific value of a Solar System survey.
Indeed, the Spaceguard Survey itself has yielded scientific results aside from the value of impact risk reduction. Recently William Bottke and his colleagues at the Southwest Research Institute in Boulder, Colorado, used orbital statistics of asteroids discovered by the surveys to propose that the event that killed off the dinosaurs came from an 'impact shower' resulting from the collisional breakup that produced the Baptistina asteroid family. The size frequency distribution of impactors is itself interesting. The drop in numbers from those of a few hundred metres in diameter to those of a few tens of metres is not yet explained, but is perhaps due to the transition, at around 200 metres diameter, from 'rubble pile' structure among larger asteroids, which are less resistant to disruption by collisions, to monolithic bodies in the smaller size range, which are more resistant to further collisional breakup. Thus, although continuing surveys for the sole purpose of risk reduction may be of diminishing value, the scientific rewards will remain high, and we can hope that ever more powerful surveys will continue in the future.
Alan Harris is a senior research scientist with the Space Science Institute, 4603 Orange Knoll Avenue, La Canada, California 91011-3364, USA.
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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 dmorrison@arc.nasa.gov. For additional information, please see the website http://impact.arc.nasa.gov. If anyone wishes to copy or redistribute original material from these notes, fully or in part, please include this disclaimer.
01 July 2008
The Planetary Society's Planetary Radio Show On Tunguska
Airdate: Monday, June 30, 2008
Running Time: 00:28:52
Listen: Windows Media | MP3
Early on the morning of June 30, 1908, a peaceful Siberian forest was suddenly leveled by the explosion of a meteor. Scientist, author and artist Bill Hartmann returns to Planetary Radio to talk about this event. Emily Lakdawalla provides another Phoenix Mars mission update. Bill Nye reports on his visit to Congress. Catch the winner of the Random Space Fact recording contest on this week's What's Up with Bruce Betts and Mat Kaplan, which includes a chance to win an Explorer's Guide to Mars poster.
Link: Planetary Radio Show (Monday, June 30, 2008)
Link: Planetary Radio (Windows Media)
Link: Planetary Radio (.mp3)
Running Time: 00:28:52
Listen: Windows Media | MP3
Early on the morning of June 30, 1908, a peaceful Siberian forest was suddenly leveled by the explosion of a meteor. Scientist, author and artist Bill Hartmann returns to Planetary Radio to talk about this event. Emily Lakdawalla provides another Phoenix Mars mission update. Bill Nye reports on his visit to Congress. Catch the winner of the Random Space Fact recording contest on this week's What's Up with Bruce Betts and Mat Kaplan, which includes a chance to win an Explorer's Guide to Mars poster.
Link: Planetary Radio Show (Monday, June 30, 2008)
Link: Planetary Radio (Windows Media)
Link: Planetary Radio (.mp3)
The Plantaery Society's NEO Fund
From an email solicitation from The Planetary Society to donate to their NEO fund.
Link: The Planetary Society NEO Fund
Dear Member,
On the 100th anniversary of the Tunguska asteroid explosion, how simply can I state Earth's situation without hyperbole? Let me give this a try:
* We know of 4,700 asteroids that could strike Earth.
* 700 of them could cause global disaster.
* We'll need to know within a few years if we need to deflect the closest NEO, Apophis, from its current orbit, or there may not be time to stop it.
* Congress is tying NASA's hands, or "blinding us" if you prefer, because of budgetary constraints.
* We have to determine the threat level without their help.
In case you were wondering, Apophis is the size of Yankee Stadium, and it's traveling at 45,000 kilometers per hour.
How likely are we to be hit and significantly damaged? The Tunguska Event occurred 100 years ago today. On that day, an asteroid exploded over Siberia, killing all life and flattening trees over 2000 square kilometers.
The Planetary Society is now working in two ways to prevent this from happening again. We are:
1. Working to keep the Arecibo Observatory in operation. It's 20 times more sensitive than any other radio-telescope instrument in the world. But it's scheduled to be closed because of budget problems.
2. Funding research through the Shoemaker NEO Grant fund. One of our recipients, Roy Tucker, is a co-discoverer of Apophis. He used his grant to buy the equipment which helped him discover Apophis.
Your support for our NEO Fund will help Shoemaker recipients, and facilities like the Arecibo Observatory, stay on watch for inbound NEOs. You'll also help develop strategies to protect us from a catastrophic hit.
Donate now and your support will help our best minds take on these all-too-real threats to our only home: Our planet Earth.
Sincerely,
Louis Friedman
Dr. Louis D. Friedman
Executive Director
P.S. As far as we now know, there are 700 NEOs heading our way that could cause global disaster. Are there more? Please donate today, so we can continue to fund NEO research.
Link: The Planetary Society NEO Fund
Dear Member,
On the 100th anniversary of the Tunguska asteroid explosion, how simply can I state Earth's situation without hyperbole? Let me give this a try:
* We know of 4,700 asteroids that could strike Earth.
* 700 of them could cause global disaster.
* We'll need to know within a few years if we need to deflect the closest NEO, Apophis, from its current orbit, or there may not be time to stop it.
* Congress is tying NASA's hands, or "blinding us" if you prefer, because of budgetary constraints.
* We have to determine the threat level without their help.
In case you were wondering, Apophis is the size of Yankee Stadium, and it's traveling at 45,000 kilometers per hour.
How likely are we to be hit and significantly damaged? The Tunguska Event occurred 100 years ago today. On that day, an asteroid exploded over Siberia, killing all life and flattening trees over 2000 square kilometers.
The Planetary Society is now working in two ways to prevent this from happening again. We are:
1. Working to keep the Arecibo Observatory in operation. It's 20 times more sensitive than any other radio-telescope instrument in the world. But it's scheduled to be closed because of budget problems.
2. Funding research through the Shoemaker NEO Grant fund. One of our recipients, Roy Tucker, is a co-discoverer of Apophis. He used his grant to buy the equipment which helped him discover Apophis.
Your support for our NEO Fund will help Shoemaker recipients, and facilities like the Arecibo Observatory, stay on watch for inbound NEOs. You'll also help develop strategies to protect us from a catastrophic hit.
Donate now and your support will help our best minds take on these all-too-real threats to our only home: Our planet Earth.
Sincerely,
Louis Friedman
Dr. Louis D. Friedman
Executive Director
P.S. As far as we now know, there are 700 NEOs heading our way that could cause global disaster. Are there more? Please donate today, so we can continue to fund NEO research.
Planetary Soceity Press Conference on Arecibo
From the Press Release..
The Planetary Society today joined with US Congressman Dana Rohrabacher, 46th District of California, to call for greater support for near-Earth object research and continued funding of the Arecibo radiotelescope to track potentially threatening objects in space. They were joined at the press conference by Alan W. Harris, Senior Research Scientist of the Space Science Institute, and Don Yeomans, Manager of NASA’s Near-Earth Object Program Office at the Jet Propulsion Laboratory.
June 30 marks the 100th anniversary of the Tunguska cataclysm when a fireball from space exploded over a Siberian forest, flattening more than 2000 square kilometers. If such an impact occurred over Los Angeles or Moscow today, the death toll would be catastrophic. The dangers our planet faces from near-Earth objects (NEOs) are the focus of The Planetary Society's year-long program, Target Earth.
Astronomers have already discovered that one asteroid, named Apophis, will pass closer to Earth in 21 years than our geosynchronous communications satellites, and its trajectory has a small probability of taking it on a collision course with Earth seven years after that. The Planetary Society awarded $50,000 in an Apophis Mission Design contest for the best idea for tagging a potentially hazardous asteroid, marking it in some way that it could be better tracked.
If an object is known to be dangerous decades before it will impact Earth, humanity will have the chance to alter the object's course and the planet's destiny.
"We can't afford to remain ignorant of a dangerous object that might be headed our way in 20, 30, or even 100 years," said Louis Friedman, Executive Director of The Planetary Society. “The lives of millions may be at stake.”
Earth orbits the solar system in a swarm of NEOs. Tracking these objects by radar is an ideal way to precisely know the probability of impact, and the Arecibo radiotelescope is the most powerful instrument for the job. However, Arecibo currently faces closure by the National Science Foundation due to lack of funds, and The Planetary Society joins its voice to many from the science community, urging Congress to reinstate the telescope's budget.
Over the past few years, our knowledge of NEOs has greatly increased as researchers have discovered and tracked many comets and asteroids that travel through our neighborhood of space. The Planetary Society has funded several NEO researchers through its Gene Shoemaker grant program. Still, many more objects remain to be found, and the orbits of many known objects need to be better refined.
Link: The Planetary Society Press Release
The Planetary Society today joined with US Congressman Dana Rohrabacher, 46th District of California, to call for greater support for near-Earth object research and continued funding of the Arecibo radiotelescope to track potentially threatening objects in space. They were joined at the press conference by Alan W. Harris, Senior Research Scientist of the Space Science Institute, and Don Yeomans, Manager of NASA’s Near-Earth Object Program Office at the Jet Propulsion Laboratory.
June 30 marks the 100th anniversary of the Tunguska cataclysm when a fireball from space exploded over a Siberian forest, flattening more than 2000 square kilometers. If such an impact occurred over Los Angeles or Moscow today, the death toll would be catastrophic. The dangers our planet faces from near-Earth objects (NEOs) are the focus of The Planetary Society's year-long program, Target Earth.
Astronomers have already discovered that one asteroid, named Apophis, will pass closer to Earth in 21 years than our geosynchronous communications satellites, and its trajectory has a small probability of taking it on a collision course with Earth seven years after that. The Planetary Society awarded $50,000 in an Apophis Mission Design contest for the best idea for tagging a potentially hazardous asteroid, marking it in some way that it could be better tracked.
If an object is known to be dangerous decades before it will impact Earth, humanity will have the chance to alter the object's course and the planet's destiny.
"We can't afford to remain ignorant of a dangerous object that might be headed our way in 20, 30, or even 100 years," said Louis Friedman, Executive Director of The Planetary Society. “The lives of millions may be at stake.”
Earth orbits the solar system in a swarm of NEOs. Tracking these objects by radar is an ideal way to precisely know the probability of impact, and the Arecibo radiotelescope is the most powerful instrument for the job. However, Arecibo currently faces closure by the National Science Foundation due to lack of funds, and The Planetary Society joins its voice to many from the science community, urging Congress to reinstate the telescope's budget.
Over the past few years, our knowledge of NEOs has greatly increased as researchers have discovered and tracked many comets and asteroids that travel through our neighborhood of space. The Planetary Society has funded several NEO researchers through its Gene Shoemaker grant program. Still, many more objects remain to be found, and the orbits of many known objects need to be better refined.
Link: The Planetary Society Press Release
30 June 2008
Move An Asteroid 2008 Technical Paper Winners Annouced
From a competition I helped organize with the Space Generation Advisory Council (SGAC). I must thank the judges at SpaceWorks, my home organization, for assisting me in reviewing all the entrants. We hope to continue this competition next year.
Space Generation Advisory Council Announces Winners of “Move An Asteroid 2008” International Competition on 100th Anniversary of Tunguska Explosion
The Space Generation Advisory Council, the world’s largest group representing youth perspectives on space exploration to the United Nations and national space programs today announced the winners of an international youth technical paper competition to develop unique and innovative concepts for how to deflect an asteroid or comet that could impact the Earth (referred to as mitigation). The SGAC announced the competition results on the 100th anniversary of the last major impact of the Earth by an asteroid or comet, known as the Tunguska explosion. Financial support for this competition is provided by Northrop Grumman Corporation, Lockheed Martin Corporation, SpaceWorks Commercial, and The Planetary Society.
First place in the competition is awarded to Mary D'Souza of the Department of Mechanical Engineering at the University of Queensland in Australia for her paper entitled “A Body Solar Sail Concept for the Deflection of 99942 Apophis.” Ms. D'Souza’s concept involves wrapping an asteroid in a reflective film (referred to as a “body” solar sail). Such a coating may increase the asteroid’s reflectivity, enabling deflection by solar radiation pressure. Ms. D'Souza will receive a trip to present her paper at this year's Space Generation Congress (SGC) and International Astronautical Congress (IAC) which take place in Glasgow, Scotland from late September until early October 2008.
Second place is awarded to Mr. Andrew Bacon of the Department of Electronic and Electrical Engineering at the University of Bath in Bath, United Kingdom for his paper entitled “The Use of Electromechanical Resonators for the Mitigation of Earth Threatening Asteroids and Comets.” Mr. Bacon’s concept involves the use of electromechanical resonators to build up waves within an asteroid or comet that would break it up. Mr. Bacon will receive a trip to present his paper at this year’s SGC.
"We received submissions from all over the world and thank all the participants for developing creative Near Earth Object (NEO) mitigation strategies. The first and second place winners demonstrated an ability to think creatively about the problem and to explain it to the judges.”, said A.C. Charania, administrator of the Move An Asteroid 2008 Competition. "We hope to continue this competition next year and look forward to the presentations of the winners at this year’s Space Generation Congress (SGC) and International Astronautical Congress (IAC)."
"It is great to see such an interest in this topic from young people all over the world. Hopefully with competitions like this, SGAC can further increase the involvement of youth in this important field of current space research.", said Alex Karl, Co-Chairperson of the Space Generation Advisory Council.
Link: Move An Asteroid 2008 Website
Link: SGAC Press Release PDF
Link: Press Release
Space Generation Advisory Council Announces Winners of “Move An Asteroid 2008” International Competition on 100th Anniversary of Tunguska Explosion
The Space Generation Advisory Council, the world’s largest group representing youth perspectives on space exploration to the United Nations and national space programs today announced the winners of an international youth technical paper competition to develop unique and innovative concepts for how to deflect an asteroid or comet that could impact the Earth (referred to as mitigation). The SGAC announced the competition results on the 100th anniversary of the last major impact of the Earth by an asteroid or comet, known as the Tunguska explosion. Financial support for this competition is provided by Northrop Grumman Corporation, Lockheed Martin Corporation, SpaceWorks Commercial, and The Planetary Society.
First place in the competition is awarded to Mary D'Souza of the Department of Mechanical Engineering at the University of Queensland in Australia for her paper entitled “A Body Solar Sail Concept for the Deflection of 99942 Apophis.” Ms. D'Souza’s concept involves wrapping an asteroid in a reflective film (referred to as a “body” solar sail). Such a coating may increase the asteroid’s reflectivity, enabling deflection by solar radiation pressure. Ms. D'Souza will receive a trip to present her paper at this year's Space Generation Congress (SGC) and International Astronautical Congress (IAC) which take place in Glasgow, Scotland from late September until early October 2008.
Second place is awarded to Mr. Andrew Bacon of the Department of Electronic and Electrical Engineering at the University of Bath in Bath, United Kingdom for his paper entitled “The Use of Electromechanical Resonators for the Mitigation of Earth Threatening Asteroids and Comets.” Mr. Bacon’s concept involves the use of electromechanical resonators to build up waves within an asteroid or comet that would break it up. Mr. Bacon will receive a trip to present his paper at this year’s SGC.
"We received submissions from all over the world and thank all the participants for developing creative Near Earth Object (NEO) mitigation strategies. The first and second place winners demonstrated an ability to think creatively about the problem and to explain it to the judges.”, said A.C. Charania, administrator of the Move An Asteroid 2008 Competition. "We hope to continue this competition next year and look forward to the presentations of the winners at this year’s Space Generation Congress (SGC) and International Astronautical Congress (IAC)."
"It is great to see such an interest in this topic from young people all over the world. Hopefully with competitions like this, SGAC can further increase the involvement of youth in this important field of current space research.", said Alex Karl, Co-Chairperson of the Space Generation Advisory Council.
Link: Move An Asteroid 2008 Website
Link: SGAC Press Release PDF
Link: Press Release
YouTube Video: "Scientists baffled by flattened forest -- 100 years on"
A century ago 2,000 square kilometres of Siberian forest were flattened in an apparent explosion. The event has puzzled scientists ever since and, although theories abound as to the cause of the blast, nobody has managed to find out exactly why 80 million trees toppled over near the Tunguska River in 1908.
Link: YouTube Video (Scientists baffled by flattened forest -- 100 years on)
YouTube Video: "A visit to the site of the Tunguska explosion"
New Scientist features editor David Cohen narrates his journey to the site of the Tunguska explosion in Siberia.
Link: YouTube Video (A visit to the site of the Tunguska explosion)
The Planetary Society's Press Release on Tunguska Anniversary
From the press release...
PRESS RELEASE
Date Released: Saturday, June 28, 2008
Source: Planetary Society - Comments Comments
Target Earth: How Prepared Are We for Another Tunguska?
100th Anniversary of Vast Explosion in Siberia
Speaking:
US Congressman Dana Rohrabacher, 46th District of California
Louis Friedman, Executive Director, The Planetary Society
Bruce Betts, Director of Projects, The Planetary Society
Alan W. Harris, Senior Research Scientist, Space Science Institute
Don Yeomans, Manager of NASA's Near-Earth Object Program Office, Jet Propulsion Laboratory
Date: Monday, June 30, 2008
Time: 11:00 AM
Place: The Planetary Society, 65 N Catalina Avenue, Pasadena, CA
A fireball from the sky exploded over the forest near Siberia's Podkamennaya Tunguska River 100 years ago today. The blast leveled 2000 square kilometers of trees, flattening them like matchsticks. Imagine what would happen if a similar object from space - probably an asteroid - exploded over one of Earth's cities today.
Join us at a press conference hosted by The Planetary Society that will feature representatives from the government, science and space advocacy outlining the threat that near-Earth objects pose to the world today and what we can do to make our planet safer.
* See images of a vast Siberian forest leveled.
* Discover what a similar explosion would do to a city like Los Angeles or New York today.
* Learn what's happening in Congress regarding saving the world's largest radiotelescope, Arecibo, to help track near-Earth objects.
* Hear what steps we are taking, and still need to take, to make our world safer from impact threats.
Participants will be available for questions during the press conference and private interviews following it. Please RSVP or call Susan Lendroth for more details, 626-793-5100 ext 237 or susan.lendroth@planetary.org.
Link: SpaceRef Press Release
PRESS RELEASE
Date Released: Saturday, June 28, 2008
Source: Planetary Society - Comments Comments
Target Earth: How Prepared Are We for Another Tunguska?
100th Anniversary of Vast Explosion in Siberia
Speaking:
US Congressman Dana Rohrabacher, 46th District of California
Louis Friedman, Executive Director, The Planetary Society
Bruce Betts, Director of Projects, The Planetary Society
Alan W. Harris, Senior Research Scientist, Space Science Institute
Don Yeomans, Manager of NASA's Near-Earth Object Program Office, Jet Propulsion Laboratory
Date: Monday, June 30, 2008
Time: 11:00 AM
Place: The Planetary Society, 65 N Catalina Avenue, Pasadena, CA
A fireball from the sky exploded over the forest near Siberia's Podkamennaya Tunguska River 100 years ago today. The blast leveled 2000 square kilometers of trees, flattening them like matchsticks. Imagine what would happen if a similar object from space - probably an asteroid - exploded over one of Earth's cities today.
Join us at a press conference hosted by The Planetary Society that will feature representatives from the government, science and space advocacy outlining the threat that near-Earth objects pose to the world today and what we can do to make our planet safer.
* See images of a vast Siberian forest leveled.
* Discover what a similar explosion would do to a city like Los Angeles or New York today.
* Learn what's happening in Congress regarding saving the world's largest radiotelescope, Arecibo, to help track near-Earth objects.
* Hear what steps we are taking, and still need to take, to make our world safer from impact threats.
Participants will be available for questions during the press conference and private interviews following it. Please RSVP or call Susan Lendroth for more details, 626-793-5100 ext 237 or susan.lendroth@planetary.org.
Link: SpaceRef Press Release
On this day...in 1908...Tunguska (roundup of several articles)
On this, the 100th anniversary of the Tunguska explosion, here is roundup of articles.
"Fire in the sky: Tunguska at 100"
Paul Rincon
BBC News
Link: BBC Article
"Huge Tunguska Explosion Remains Mysterious 100 Years Later"
Link: Space.com article
"Tunguska: The day the sky exploded"
Link: NewScientist article
"Asteroid anniversary recalls Earth's rocky history"
Link: USAToday article
"June 30, 1908: A Very Close Encounter of the Second Kind"
Link: Wired.com article
"Apocalypse Then. Next One, When?"
Andrew C. Revkin
30 June 2008
Link: New York Times article
"The Tunguska Event: A Century Later, It’s Still Mysterious"
Link: Discover Magazine article
"Target Earth: Hie Prepared Are We"
Planetary Society Press Release
26 June 2008
Link: Planetary Society Press Release
"Tunguska: 100 Years and Counting"
J. Kelly Beatty
30 June 2008
Link: Sky and Telescope Article
"The Tunguska Event--100 Years Later"
30 June 2008
Link: NASA News Article
Link: NASA Article Podcast (.mp3)
"A Century of Tunguska"
30 June 2008
Link: Archy Article on Tunguska
"Impact Earth: Avoiding another asteroid"
02 July 2008
Link: The Independent Article
"Fire in the sky: Tunguska at 100"
Paul Rincon
BBC News
Link: BBC Article
"Huge Tunguska Explosion Remains Mysterious 100 Years Later"
Link: Space.com article
"Tunguska: The day the sky exploded"
Link: NewScientist article
"Asteroid anniversary recalls Earth's rocky history"
Link: USAToday article
"June 30, 1908: A Very Close Encounter of the Second Kind"
Link: Wired.com article
"Apocalypse Then. Next One, When?"
Andrew C. Revkin
30 June 2008
Link: New York Times article
"The Tunguska Event: A Century Later, It’s Still Mysterious"
Link: Discover Magazine article
"Target Earth: Hie Prepared Are We"
Planetary Society Press Release
26 June 2008
Link: Planetary Society Press Release
"Tunguska: 100 Years and Counting"
J. Kelly Beatty
30 June 2008
Link: Sky and Telescope Article
"The Tunguska Event--100 Years Later"
30 June 2008
Link: NASA News Article
Link: NASA Article Podcast (.mp3)
"A Century of Tunguska"
30 June 2008
Link: Archy Article on Tunguska
"Impact Earth: Avoiding another asteroid"
02 July 2008
Link: The Independent Article
29 June 2008
Article: German Smallsat NEO Detection Mission (similar to Canadian NEOSSat)
Similar to the Canadian NEOSSat mission, from the article...
German scientists said Thursday they are planning a satellite especially to hunt space rocks that might slam into the planet Earth and wipe out complete cities or countries. The modest satellite, costing 15 million euros (24 million dollars), would scan space for near earth objects. An NEO is a celestial body which orbits the Sun on a track that crosses Earth's orbit.
The German space agency DLR said modelling showed there must be more than 1,000 such objects more than 100 metres wide, but only nine have been discovered so far.
It spoke as the centenary approaches of the June 30, 1908 Tunguska Event.
The DLR said its interpretation of that event was that a rock 30 to 50 metres wide entered the atmosphere over Siberia and exploded 8 to 12 kilometres above the surface, destroying 2,000 square kilometres of forest.
"It's vital to identify NEOs before they get onto a collision course with the Earth," said Ekkehard Kührt of the DLR planetary research institute.
Development work on the satellite is probably to begin this autumn. The satellite would also track space junk, which consists of satellite debris orbiting the Earth.
DLR says that with sufficient warning time, such as 10 years, an NEO could be nudged away into an orbit that did not threaten the Earth. A spacecraft could crash into the NEO and knock off a chunk, leading to a change in the NEO's track.
Earth Times
26 June 2008
Link: Earth Times Article
German scientists said Thursday they are planning a satellite especially to hunt space rocks that might slam into the planet Earth and wipe out complete cities or countries. The modest satellite, costing 15 million euros (24 million dollars), would scan space for near earth objects. An NEO is a celestial body which orbits the Sun on a track that crosses Earth's orbit.
The German space agency DLR said modelling showed there must be more than 1,000 such objects more than 100 metres wide, but only nine have been discovered so far.
It spoke as the centenary approaches of the June 30, 1908 Tunguska Event.
The DLR said its interpretation of that event was that a rock 30 to 50 metres wide entered the atmosphere over Siberia and exploded 8 to 12 kilometres above the surface, destroying 2,000 square kilometres of forest.
"It's vital to identify NEOs before they get onto a collision course with the Earth," said Ekkehard Kührt of the DLR planetary research institute.
Development work on the satellite is probably to begin this autumn. The satellite would also track space junk, which consists of satellite debris orbiting the Earth.
DLR says that with sufficient warning time, such as 10 years, an NEO could be nudged away into an orbit that did not threaten the Earth. A spacecraft could crash into the NEO and knock off a chunk, leading to a change in the NEO's track.
Earth Times
26 June 2008
Link: Earth Times Article
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