From Dave Morrison at NASA...
NEO News (12/28/07) Odds of Mars Impact Increase
Date Released: Friday, December 28, 2007
Source: Jet Propulsion Laboratory
Updated Dec. 28, 2007 -- Astronomers have identified asteroid 2007 WD 5 in archival imagery. With these new observations, scientists at NASA's Near-Earth Object Program Office at the Jet Propulsion Laboratory in Pasadena, Calif have refined their trajectory estimates for the asteroid. Based on this latest analysis, the odds for the asteroid impacting Mars on Jan. 30 are now 1-in-25 -- or about 4 percent.
Note from David Morrison: In case of a close pass (but a miss), it is normal for the impact odds to increase before they drop to zero. This is because there is a time, as knowledge of the orbit improves, when the error ellipse (the uncertainty in the miss distance) shrinks while the target (in this case Mars) remains within the ellipse. Thus the change in odds of a hit from 1 in 75 to 1 in 25 does not mean it will hit -- it still has a 96% chance of missing -- but it sure is interesting! It would be even more "interesting" if the target were Earth not Mars. Think about it.
-------------------------------
WASHINGTON - Astronomers funded by NASA are monitoring the trajectory of an asteroid estimated to be 50 meters (164 feet) wide that is expected to cross Mars' orbital path early next year. Observations provided by the astronomers and analyzed by NASA's Near-Earth Object Office at the Jet Propulsion Laboratory in Pasadena, Calif., indicate the object may pass within 30,000 miles of Mars at about 6 a.m. EST (3 a.m. PST) on Jan. 30, 2008.
"Right now asteroid 2007 WD5 is about half-way between Earth and Mars and closing the distance at a speed of about 27,900 miles per hour," said Don Yeomans, manager of the Near Earth Object Office at JPL. "Over the next five weeks, we hope to gather more information from observatories so we can further refine the asteroid's trajectory."
NASA detects and tracks asteroids and comets passing close to Earth. The Near Earth Object Observation Program, commonly called "Spaceguard," plots the orbits of these objects to determine if any could be potentially hazardous to our planet.
Asteroid 2007 WD5 was first discovered on Nov. 20, 2007, by the NASA-funded Catalina Sky Survey and put on a "watch list" because its orbit passes near Earth. Further observations from both the NASA-funded Spacewatch at Kitt Peak, Ariz., and the Magdalena Ridge Observatory in New Mexico gave scientists enough data to determine that the asteroid was not a danger to Earth, but could potentially impact Mars. This makes it a member of an interesting class of small objects that are both near Earth objects and "Mars crossers."
Because of current uncertainties about the asteroid's exact orbit, there is a 1-in-75 chance of 2007 WD5 impacting Mars. If this unlikely event were to occur, it would be somewhere within a broad swath across the planet north of where the Opportunity rover is located.
"We estimate such impacts occur on Mars every thousand years or so," said Steve Chesley, a scientist at JPL. "If 2007 WD5 were to thump Mars on Jan. 30, we calculate it would hit at about 30,000 miles per hour and might create a crater more than half-a-mile wide." The Mars Rover Opportunity is exploring a crater approximately this size right now.
Such a collision could release about three megatons of energy. Scientists believe an event of comparable magnitude occurred here on Earth in 1908 in Tunguska, Siberia, but no crater was created. The object was disintegrated by Earth's thicker atmosphere before it hit the ground, although the air blast devastated a large area of unpopulated forest.
NASA and its partners will continue to track asteroid 2007 WD5 and will provide an update in January when further information is available. For more information on the Near Earth Object program, visit: http://neo.jpl.nasa.gov/.
An audio interview/podcast regarding 2007 WD5 is available at: http://www.jpl.nasa.gov/multimedia/podcast/mars-asteroid-20071221/
A videofile related to this story is available on NASA TV and the Web. For information and schedules, visit: http://www.nasa.gov/ntv.
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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.
31 December 2007
21 December 2007
Planetary Society Blog Update on 2007 WD5 (with additional Chesley comments)
From the Planetary Society Blog (Emily Lakdawalla):
"WD5 is approximately 50 meters in diameter, so if it did hit, it would be a good-sized bang, producing a crater about a kilometer in diameter. (This is pretty close to the size of Victoria crater, Opportunity's haunt.) Chesley estimates that such a bang happens on Mars about once every thousand years."
"However, Chesley says that this size of an impact should create a dust plume that could be detected by one of the orbiters; even the rovers could detect a change in the dust component of the sky. And of course a 1-kilometer crater would be a pretty big target for HiRISE and CRISM on Mars Reconnaissance Orbiter -- in fact, that's quite big enough to be an interesting target for all the cameras on all the orbiters at Mars. You'd probably need to spot it first with one of the lower-resolution cameras, then zero in for a detailed look with one of the higher-resolution ones."
Link: Planetary Society Blog Entry 21 December 2007: "Alert the Martian Defense Force!"
"WD5 is approximately 50 meters in diameter, so if it did hit, it would be a good-sized bang, producing a crater about a kilometer in diameter. (This is pretty close to the size of Victoria crater, Opportunity's haunt.) Chesley estimates that such a bang happens on Mars about once every thousand years."
"However, Chesley says that this size of an impact should create a dust plume that could be detected by one of the orbiters; even the rovers could detect a change in the dust component of the sky. And of course a 1-kilometer crater would be a pretty big target for HiRISE and CRISM on Mars Reconnaissance Orbiter -- in fact, that's quite big enough to be an interesting target for all the cameras on all the orbiters at Mars. You'd probably need to spot it first with one of the lower-resolution cameras, then zero in for a detailed look with one of the higher-resolution ones."
Link: Planetary Society Blog Entry 21 December 2007: "Alert the Martian Defense Force!"
JPL News Release and PodCast on 2007 WD5
The current position of asteroid 2007 WD5, with its orbit shown in blue. The asteroid's orbit stretches from just outside the Earth's orbit at its closest point to the Sun, to the outer reaches of the asteroid belt at its farthest.
This artist rendering uses an arrow to show the predicted path of the asteroid on Jan. 30, 2008, and the orange swath indicates the area it is expected to pass through. Mars may or may not be in its path. Image credit: NASA/JPL
Link: JPL New Release
Link: JPL Podcast
NASA News release on 2007 WD5
From the article...
Astronomers funded by NASA are monitoring the trajectory of an asteroid estimated to be 164-feet wide that is expected to cross Mars' orbital path early next year. Observations provided by the astronomers and analyzed by NASA's Near-Earth Object Office at the Jet Propulsion Laboratory in Pasadena, Calif., indicate the object may pass within 30,000 miles of Mars at about 6 a.m. EST on Jan. 30, 2008.
"Right now asteroid 2007 WD5 is about half-way between the Earth and Mars and closing the distance at a speed of about 27,900 miles per hour," said Don Yeomans, manager of the Near Earth Object Office at JPL. "Over the next five weeks, we hope to gather more information from observatories so we can further refine the asteroid's trajectory."
Asteroid 2007 WD5 was first discovered on Nov. 20, 2007, by the NASA-funded Catalina Sky Survey and put on a "watch list" because its orbit passes near the Earth. Further observations from both the NASA-funded Spacewatch at Kitt Peak, Ariz., and the Magdalena Ridge Observatory in New Mexico gave scientists enough data to determine that the asteroid was not a danger to Earth, but could potentially impact Mars. This makes it a member of an interesting class of small objects that are both Near Earth Objects and “Mars crossers."
Because of current uncertainties about the asteroid's exact orbit, there is a 1-in-75 chance of 2007 WD5 impacting Mars. If this unlikely event were to occur, it would be somewhere within a broad swath across the planet north of where the Opportunity rover is.
"Astronomers Monitor Asteroid to Pass Near Mars"
NASA
21 December 2007
Link: NASA News Release
Astronomers funded by NASA are monitoring the trajectory of an asteroid estimated to be 164-feet wide that is expected to cross Mars' orbital path early next year. Observations provided by the astronomers and analyzed by NASA's Near-Earth Object Office at the Jet Propulsion Laboratory in Pasadena, Calif., indicate the object may pass within 30,000 miles of Mars at about 6 a.m. EST on Jan. 30, 2008.
"Right now asteroid 2007 WD5 is about half-way between the Earth and Mars and closing the distance at a speed of about 27,900 miles per hour," said Don Yeomans, manager of the Near Earth Object Office at JPL. "Over the next five weeks, we hope to gather more information from observatories so we can further refine the asteroid's trajectory."
Asteroid 2007 WD5 was first discovered on Nov. 20, 2007, by the NASA-funded Catalina Sky Survey and put on a "watch list" because its orbit passes near the Earth. Further observations from both the NASA-funded Spacewatch at Kitt Peak, Ariz., and the Magdalena Ridge Observatory in New Mexico gave scientists enough data to determine that the asteroid was not a danger to Earth, but could potentially impact Mars. This makes it a member of an interesting class of small objects that are both Near Earth Objects and “Mars crossers."
Because of current uncertainties about the asteroid's exact orbit, there is a 1-in-75 chance of 2007 WD5 impacting Mars. If this unlikely event were to occur, it would be somewhere within a broad swath across the planet north of where the Opportunity rover is.
"Astronomers Monitor Asteroid to Pass Near Mars"
NASA
21 December 2007
Link: NASA News Release
Update on Tunguska Mars (2007 WD5) Close Approach
My colleagues at SpaceWorks have done some quick propagation of 2007 WD5 using our own internal trajectory propagator. Here are some preliminary results using our IHOP (Interplanetary High-fidelity Orbit Propagator) tool:
Using an internally-developed orbit propagation tool, SpaceWorks Engineering, Inc. (SEI) has verified the predicted date for the 2007 WD5 close approach to Mars on January 30, 2008. Starting from the publicly available NASA JPL HORIZONS system orbital elements for 2007 WD5 for December 21, 2007, IHOP predicts that the asteroid 2007 WD5 will pass within 51,720 km (32,137 miles) of Mars on Wednesday, January 30, 2008 at 4:10 AM Eastern Standard Time-EST (09:10:22.1 UTC, Julian date 2454495.88220).
The internal tool, dubbed IHOP (Interplanetary High-fidelity Orbit Propagator), is a Java-based n-body propagator that utilizes a 7th/8th order Runge-Kutta-Fehlberg numerical integrator to propagate small bodies in the solar system. The orbit propagator includes the gravitational accelerations induced by the sun, the planets, and Earth's moon.
Link: SpaceWorks Engineering, Inc. (SEI)
Using an internally-developed orbit propagation tool, SpaceWorks Engineering, Inc. (SEI) has verified the predicted date for the 2007 WD5 close approach to Mars on January 30, 2008. Starting from the publicly available NASA JPL HORIZONS system orbital elements for 2007 WD5 for December 21, 2007, IHOP predicts that the asteroid 2007 WD5 will pass within 51,720 km (32,137 miles) of Mars on Wednesday, January 30, 2008 at 4:10 AM Eastern Standard Time-EST (09:10:22.1 UTC, Julian date 2454495.88220).
The internal tool, dubbed IHOP (Interplanetary High-fidelity Orbit Propagator), is a Java-based n-body propagator that utilizes a 7th/8th order Runge-Kutta-Fehlberg numerical integrator to propagate small bodies in the solar system. The orbit propagator includes the gravitational accelerations induced by the sun, the planets, and Earth's moon.
Link: SpaceWorks Engineering, Inc. (SEI)
Follow on Tunguska Mars from Dave Morrison's NEO News
From Dave Morrison's NEO News (12/21/07):
NEO News (12/21/07) "Tunguska" on Mars?
Remarkably, the Spaceguard Survey has discovered a small NEA that might hit Mars, not Earth, Orbit calculations from JPL indicate that Asteroid 2007 WD5 is on a trajectory that will bring it close to Mars on January 30, with a chance of hitting (based on the current uncertainty in the orbit) of better than 1%. Only once (3 years ago) has the orbital analysis of a NEA indicated a higher probability of impact, and the target then was Earth. For about two days around Christmas, 2004, the calculated impact probability for NEA Apophis was better than 1%, reaching a maximum of slightly greater than 1 in 50. Of course, additional orbital data then showed that while Apophis would come close in April 2029, it would not hit. The same thing will probably happen with this orbital analysis of 2007 WD5. But those of us in the business of surveying for possible impacts must always consider the possibility of a hit, even if the odds are against it. Should 2007 WD5 actually hit Mars, it would have an impact energy similar to that of the 1908 Tunguska impact on Earth, making a roughly 1-km-diameter crater. This crater, with its freshly exposed ejecta, would be extremely interesting to study from several spacecraft now in orbit around Mars. We can hope that this might happen, providing us a new window into the martian subsurface -- but the most likely ending for this story will be a miss, with 2007 WD5 quickly fading from memory.
Below are two press stories about 2007 WD5, and another reporting on the work of Mark Boslough on Tunguska, which was discussed in NEO News for December 18.
David Morrison
=====================================
ASTEROID ON TRACK FOR POSSIBLE MARS HIT
By John Johnson Jr., Los Angeles Times Staff Writer
December 21, 2007
Talk about your cosmic pileups. An asteroid similar to the one that flattened forests in Siberia in 1908 could plow into Mars next month, scientists said Thursday.
Researchers attached to NASA's Near-Earth Object Program, who sometimes jokingly call themselves the Solar System Defense Team, have been tracking the asteroid since its discovery in late November. The scientists, at the Jet Propulsion Laboratory in La Cañada Flintridge, put the chances that it will hit the Red Planet on Jan. 30 at about 1 in 75.
A 1-in-75 shot is "wildly unusual," said Steve Chesley, an astronomer with the Near-Earth Object office, which routinely tracks about 5,000 objects in Earth's neighborhood. "We're used to dealing with odds like one-in-a-million," Chesley said. "Something with a one-in-a-hundred chance makes us sit up straight in our chairs."
The asteroid, designated 2007 WD5, is about 160 feet across, which puts it in the range of the space rock that exploded over Siberia. That explosion, the largest impact event in recent history, felled 80 million trees over 830 square miles.
The Tunguska object broke up in midair, but the Martian atmosphere is so thin that an asteroid would probably plummet to the surface, digging a crater half a mile wide, Chesley said.
The impact would probably send dust high into the atmosphere, scientists said. Depending on where the asteroid hit, such a plume might be visible through telescopes on Earth, Chesley said. The Mars Reconnaissance Orbiter, which is mapping the planet, would have a front-row seat. And NASA's two JPL-built rovers, Opportunity and Spirit, might be able to take pictures from the ground.
Because scientists have never observed an asteroid impact -- the closest thing being the 1994 collision of comet Shoemaker-Levy with Jupiter -- such a collision on Mars would produce a "scientific bonanza," Chesley said. The asteroid is now behind the moon, he said, so it will be almost two weeks before observers can plot its course more accurately.
The possibility of an impact has the Solar System Defense Team excited. "Normally, we're rooting against the asteroid," when it has Earth in its cross hairs, Chesley said. "This time we're rooting for the asteroid to hit."
==============================
ASTEROID MAY HIT MARS IN NEXT MONTH
By Alicia Chang (MSNBC & AP)
LOS ANGELES (AP) - Mars could be in for an asteroid hit. A newly discovered hunk of space rock has a 1 in 75 chance of slamming into the Red Planet on Jan. 30, scientists said Thursday.
"These odds are extremely unusual. We frequently work with really long odds when we track ... threatening asteroids," said Steve Chesley, an astronomer with the Near Earth Object Program at NASA's Jet Propulsion Laboratory.
The asteroid, known as 2007 WD5, was discovered in late November and is similar in size to an object that hit remote central Siberia in 1908, unleashing energy equivalent to a 15-megaton nuclear bomb and wiping out 60 million trees.
Scientists tracking the asteroid, currently halfway between Earth and Mars, initially put the odds of impact at 1 in 350 but increased the chances this week. Scientists expect the odds to diminish again early next month after getting new observations of the asteroid's orbit, Chesley said. "We know that it's going to fly by Mars and most likely going to miss, but there's a possibility of an impact," he said.
If the asteroid does smash into Mars, it will probably hit near the equator close to where the rover Opportunity has been exploring the Martian plains since 2004. The robot is not in danger because it lies outside the impact zone. Speeding at 8 miles a second, a collision would carve a hole the size of the famed Meteor Crater in Arizona.
In 1994, fragments of the comet Shoemaker-Levy 9 smacked into Jupiter, creating a series of overlapping fireballs in space. Astronomers have yet to witness an asteroid impact with another planet. "Unlike an Earth impact, we're not afraid, but we're excited," Chesley said.
===================================
SMALL ASTEROIDS POSE BIG NEW THREAT
By Charles Q. Choi, SPACE.com
19 December 2007
The infamous Tunguska explosion, which mysteriously leveled an area of Siberian forest nearly the size of Tokyo a century ago, might have been caused by an impacting asteroid far smaller than previously thought.
The fact that a relatively small asteroid could still cause such a massive explosion suggests "we should be making more efforts at detecting the smaller ones than we have till now," said researcher Mark Boslough, a physicist at Sandia National Laboratory in Albuquerque, N.M.
The explosion near the Podkamennaya Tunguska River on June 30, 1908, flattened some 500,000 acres (2,000 square kilometers) of Siberian forest. Scientists calculated the Tunguska explosion could have been roughly as strong as 10 to 20 megatons of TNT - 1,000 times more powerful than the atom bomb dropped on Hiroshima.
Wild theories have been bandied about for a century regarding what caused the Tunguska explosion, including a UFO crash, antimatter, a black hole and famed inventor Nikola Tesla's "death ray." In the last decade, researchers have conjectured the event was triggered by an asteroid exploding in Earth's atmosphere that was roughly 100 feet wide (30 meters) and 560,000 metric tons in mass - more than 10 times that of the Titanic.
The space rock is thought to have blown up above the surface, only fragments possibly striking the ground.
Now new supercomputer simulations suggest "the asteroid that caused the extensive damage was much smaller than we had thought," Boslough said. Specifically, he and his colleagues say it would have been a factor of three or four smaller in mass and perhaps 65 feet (20 meters) in diameter.
The simulations run on Sandia's Red Storm supercomputer - the third fastest in the world - detail how an asteroid that explodes as it runs into Earth's atmosphere will generate a supersonic jet of expanding superheated gas. This fireball would have caused blast waves that were stronger at the surface than previously thought.
At the same time, previous estimates seem to have overstated the devastation the event caused. The forest back then was not healthy, according to foresters, "and it doesn't take as much energy to blow down a diseased tree than a healthy tree," Boslough said. In addition, the winds from the explosion would naturally get amplified above ridgelines, making the explosion seem more powerful than it actually was. What scientists had thought to be an explosion between 10 and 20 megatons was more likely only three to five megatons, he explained.
All in all, the researchers suggest that smaller asteroids may pose a greater danger than previously believed. Moreover, "there are a lot more objects that size," Boslough told SPACE.com.
NASA Ames Research Center planetary scientist and astrobiologist David Morrison, who did not participate in this study, said, "If he's right, we can expect more Tunguska-sized explosions - perhaps every couple of centuries instead of every millennia or two." He added, "It raises the bar in the long term - ultimately, we'd like to have a survey system that can detect things this small."
Boslough and his colleagues detailed their findings at the American Geophysical Union meeting in San Francisco on Dec. 11. A paper on the phenomenon has been accepted for publication in the International Journal of Impact Engineering.
--
+++++++++++++++++++++++++++++++++++++++++++
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.
NEO News (12/21/07) "Tunguska" on Mars?
Remarkably, the Spaceguard Survey has discovered a small NEA that might hit Mars, not Earth, Orbit calculations from JPL indicate that Asteroid 2007 WD5 is on a trajectory that will bring it close to Mars on January 30, with a chance of hitting (based on the current uncertainty in the orbit) of better than 1%. Only once (3 years ago) has the orbital analysis of a NEA indicated a higher probability of impact, and the target then was Earth. For about two days around Christmas, 2004, the calculated impact probability for NEA Apophis was better than 1%, reaching a maximum of slightly greater than 1 in 50. Of course, additional orbital data then showed that while Apophis would come close in April 2029, it would not hit. The same thing will probably happen with this orbital analysis of 2007 WD5. But those of us in the business of surveying for possible impacts must always consider the possibility of a hit, even if the odds are against it. Should 2007 WD5 actually hit Mars, it would have an impact energy similar to that of the 1908 Tunguska impact on Earth, making a roughly 1-km-diameter crater. This crater, with its freshly exposed ejecta, would be extremely interesting to study from several spacecraft now in orbit around Mars. We can hope that this might happen, providing us a new window into the martian subsurface -- but the most likely ending for this story will be a miss, with 2007 WD5 quickly fading from memory.
Below are two press stories about 2007 WD5, and another reporting on the work of Mark Boslough on Tunguska, which was discussed in NEO News for December 18.
David Morrison
=====================================
ASTEROID ON TRACK FOR POSSIBLE MARS HIT
By John Johnson Jr., Los Angeles Times Staff Writer
December 21, 2007
Talk about your cosmic pileups. An asteroid similar to the one that flattened forests in Siberia in 1908 could plow into Mars next month, scientists said Thursday.
Researchers attached to NASA's Near-Earth Object Program, who sometimes jokingly call themselves the Solar System Defense Team, have been tracking the asteroid since its discovery in late November. The scientists, at the Jet Propulsion Laboratory in La Cañada Flintridge, put the chances that it will hit the Red Planet on Jan. 30 at about 1 in 75.
A 1-in-75 shot is "wildly unusual," said Steve Chesley, an astronomer with the Near-Earth Object office, which routinely tracks about 5,000 objects in Earth's neighborhood. "We're used to dealing with odds like one-in-a-million," Chesley said. "Something with a one-in-a-hundred chance makes us sit up straight in our chairs."
The asteroid, designated 2007 WD5, is about 160 feet across, which puts it in the range of the space rock that exploded over Siberia. That explosion, the largest impact event in recent history, felled 80 million trees over 830 square miles.
The Tunguska object broke up in midair, but the Martian atmosphere is so thin that an asteroid would probably plummet to the surface, digging a crater half a mile wide, Chesley said.
The impact would probably send dust high into the atmosphere, scientists said. Depending on where the asteroid hit, such a plume might be visible through telescopes on Earth, Chesley said. The Mars Reconnaissance Orbiter, which is mapping the planet, would have a front-row seat. And NASA's two JPL-built rovers, Opportunity and Spirit, might be able to take pictures from the ground.
Because scientists have never observed an asteroid impact -- the closest thing being the 1994 collision of comet Shoemaker-Levy with Jupiter -- such a collision on Mars would produce a "scientific bonanza," Chesley said. The asteroid is now behind the moon, he said, so it will be almost two weeks before observers can plot its course more accurately.
The possibility of an impact has the Solar System Defense Team excited. "Normally, we're rooting against the asteroid," when it has Earth in its cross hairs, Chesley said. "This time we're rooting for the asteroid to hit."
==============================
ASTEROID MAY HIT MARS IN NEXT MONTH
By Alicia Chang (MSNBC & AP)
LOS ANGELES (AP) - Mars could be in for an asteroid hit. A newly discovered hunk of space rock has a 1 in 75 chance of slamming into the Red Planet on Jan. 30, scientists said Thursday.
"These odds are extremely unusual. We frequently work with really long odds when we track ... threatening asteroids," said Steve Chesley, an astronomer with the Near Earth Object Program at NASA's Jet Propulsion Laboratory.
The asteroid, known as 2007 WD5, was discovered in late November and is similar in size to an object that hit remote central Siberia in 1908, unleashing energy equivalent to a 15-megaton nuclear bomb and wiping out 60 million trees.
Scientists tracking the asteroid, currently halfway between Earth and Mars, initially put the odds of impact at 1 in 350 but increased the chances this week. Scientists expect the odds to diminish again early next month after getting new observations of the asteroid's orbit, Chesley said. "We know that it's going to fly by Mars and most likely going to miss, but there's a possibility of an impact," he said.
If the asteroid does smash into Mars, it will probably hit near the equator close to where the rover Opportunity has been exploring the Martian plains since 2004. The robot is not in danger because it lies outside the impact zone. Speeding at 8 miles a second, a collision would carve a hole the size of the famed Meteor Crater in Arizona.
In 1994, fragments of the comet Shoemaker-Levy 9 smacked into Jupiter, creating a series of overlapping fireballs in space. Astronomers have yet to witness an asteroid impact with another planet. "Unlike an Earth impact, we're not afraid, but we're excited," Chesley said.
===================================
SMALL ASTEROIDS POSE BIG NEW THREAT
By Charles Q. Choi, SPACE.com
19 December 2007
The infamous Tunguska explosion, which mysteriously leveled an area of Siberian forest nearly the size of Tokyo a century ago, might have been caused by an impacting asteroid far smaller than previously thought.
The fact that a relatively small asteroid could still cause such a massive explosion suggests "we should be making more efforts at detecting the smaller ones than we have till now," said researcher Mark Boslough, a physicist at Sandia National Laboratory in Albuquerque, N.M.
The explosion near the Podkamennaya Tunguska River on June 30, 1908, flattened some 500,000 acres (2,000 square kilometers) of Siberian forest. Scientists calculated the Tunguska explosion could have been roughly as strong as 10 to 20 megatons of TNT - 1,000 times more powerful than the atom bomb dropped on Hiroshima.
Wild theories have been bandied about for a century regarding what caused the Tunguska explosion, including a UFO crash, antimatter, a black hole and famed inventor Nikola Tesla's "death ray." In the last decade, researchers have conjectured the event was triggered by an asteroid exploding in Earth's atmosphere that was roughly 100 feet wide (30 meters) and 560,000 metric tons in mass - more than 10 times that of the Titanic.
The space rock is thought to have blown up above the surface, only fragments possibly striking the ground.
Now new supercomputer simulations suggest "the asteroid that caused the extensive damage was much smaller than we had thought," Boslough said. Specifically, he and his colleagues say it would have been a factor of three or four smaller in mass and perhaps 65 feet (20 meters) in diameter.
The simulations run on Sandia's Red Storm supercomputer - the third fastest in the world - detail how an asteroid that explodes as it runs into Earth's atmosphere will generate a supersonic jet of expanding superheated gas. This fireball would have caused blast waves that were stronger at the surface than previously thought.
At the same time, previous estimates seem to have overstated the devastation the event caused. The forest back then was not healthy, according to foresters, "and it doesn't take as much energy to blow down a diseased tree than a healthy tree," Boslough said. In addition, the winds from the explosion would naturally get amplified above ridgelines, making the explosion seem more powerful than it actually was. What scientists had thought to be an explosion between 10 and 20 megatons was more likely only three to five megatons, he explained.
All in all, the researchers suggest that smaller asteroids may pose a greater danger than previously believed. Moreover, "there are a lot more objects that size," Boslough told SPACE.com.
NASA Ames Research Center planetary scientist and astrobiologist David Morrison, who did not participate in this study, said, "If he's right, we can expect more Tunguska-sized explosions - perhaps every couple of centuries instead of every millennia or two." He added, "It raises the bar in the long term - ultimately, we'd like to have a survey system that can detect things this small."
Boslough and his colleagues detailed their findings at the American Geophysical Union meeting in San Francisco on Dec. 11. A paper on the phenomenon has been accepted for publication in the International Journal of Impact Engineering.
--
+++++++++++++++++++++++++++++++++++++++++++
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.
Article: "Asteroid May Hit Mars in Next Month"
Our firm, SpaceWorks Engineering, Inc. (SEI) has been reviewing this object and may have some additional analysis on this object.
From the article...
A newly discovered hunk of space rock has a 1 in 75 chance of slamming into the Red Planet on Jan. 30, scientists said Thursday.
"These odds are extremely unusual. We frequently work with really long odds when we track ... threatening asteroids," said Steve Chesley, an astronomer with the Near Earth Object Program at NASA's Jet Propulsion Laboratory.
The asteroid, known as 2007 WD5, was discovered in late November and is similar in size to an object that hit remote central Siberia in 1908, unleashing energy equivalent to a 15-megaton nuclear bomb and wiping out 60 million trees.
Scientists tracking the asteroid, currently halfway between Earth and Mars, initially put the odds of impact at 1 in 350 but increased the chances this week. Scientists expect the odds to diminish again early next month after getting new observations of the asteroid's orbit, Chesley said.
"Asteroid May Hit Mars in Next Month"
Alicia Chang
Associated Press
20 December 2007
Link: Article
Another article from the LA Times has more information:
The asteroid is now behind the moon, he said, so it will be almost two weeks before observers can plot its course more accurately.
"Normally, we're rooting against the asteroid," when it has Earth in its cross hairs, Chesley said. "This time we're rooting for the asteroid to hit."
"Asteroid on track for possible Mars hit"
John Johnson Jr.
Los Angeles Times Staff Writer
21 December 2007
Link: LA Times article
Link: JPL Orbit Diagram of 2007 WD5
From the article...
A newly discovered hunk of space rock has a 1 in 75 chance of slamming into the Red Planet on Jan. 30, scientists said Thursday.
"These odds are extremely unusual. We frequently work with really long odds when we track ... threatening asteroids," said Steve Chesley, an astronomer with the Near Earth Object Program at NASA's Jet Propulsion Laboratory.
The asteroid, known as 2007 WD5, was discovered in late November and is similar in size to an object that hit remote central Siberia in 1908, unleashing energy equivalent to a 15-megaton nuclear bomb and wiping out 60 million trees.
Scientists tracking the asteroid, currently halfway between Earth and Mars, initially put the odds of impact at 1 in 350 but increased the chances this week. Scientists expect the odds to diminish again early next month after getting new observations of the asteroid's orbit, Chesley said.
"Asteroid May Hit Mars in Next Month"
Alicia Chang
Associated Press
20 December 2007
Link: Article
Another article from the LA Times has more information:
The asteroid is now behind the moon, he said, so it will be almost two weeks before observers can plot its course more accurately.
"Normally, we're rooting against the asteroid," when it has Earth in its cross hairs, Chesley said. "This time we're rooting for the asteroid to hit."
"Asteroid on track for possible Mars hit"
John Johnson Jr.
Los Angeles Times Staff Writer
21 December 2007
Link: LA Times article
Link: JPL Orbit Diagram of 2007 WD5
19 December 2007
NEO News (12/19/07) Tunguska Revision & New Book
From David Morrison...
NEO News (12/19/07) Tunguska Revision & New Book
Season's greetings and best wishes for a good new year!
The main story in this edition of NEO News concerns a proposed downsizing of the energy of the 1908 Tunguska airburst, with associated increase in the expected frequency of such impacts. Mark Boslough of Sandia has generated supercomputer simulations of the Tunguska atmospheric explosion. In part his models require less energy in the explosion because he includes the substantial downward momentum of the rocky impactor, rather then modeling it as a stationary explosion. If this revision (down to an estimated energy of 3-5 megatons, and a corresponding diameter of about 50 meters) is correct, the expected frequency of such impacts changes, from once in a couple of millennia to once in a few hundred years. If smaller impactors can do the damage previously associated with larger ones, of course, the total hazard from such impacts is increased.
The second item below is an announcement of publication of a new multi-author book "Comet/Asteroid Impacts and Human Society."
David Morrison
===================================
NEW ESTIMATE OF TUNGUSKA IMPACTOR SIZE
Sandia: December 17, 2007
ALBUQUERQUE, N.M. - The stunning amount of forest devastation at Tunguska a century ago in Siberia may have been caused by an asteroid only a fraction as large as previously published estimates, Sandia National Laboratories supercomputer simulations suggest.
"The asteroid that caused the extensive damage was much smaller than we had thought," says Sandia principal investigator Mark Boslough of the impact that occurred June 30, 1908. "That such a small object can do this kind of destruction suggests that smaller asteroids are something to consider. Their smaller size indicates such collisions are not as improbable as we had believed." Because smaller asteroids approach Earth statistically more frequently than larger ones, he says, "We should be making more efforts at detecting the smaller ones than we have till now."
The new simulation -- which more closely matches the widely known facts of destruction than earlier models -- shows that the center of mass of an asteroid exploding above the ground is transported downward at speeds faster than sound. It takes the form of a high-temperature jet of expanding gas called a fireball. This causes stronger blast waves and thermal radiation pulses at the surface than would be predicted by an explosion limited to the height at which the blast was initiated.
"Our understanding was oversimplified," says Boslough, "We no longer have to make the same simplifying assumptions, because present-day supercomputers allow us to do things with high resolution in 3-D. Everything gets clearer as you look at things with more refined tools."
The new interpretation also accounts for the fact that winds were amplified above ridgelines where trees tended to be blown down, and that the forest at the time of the explosion, according to foresters, was not healthy. Thus previous scientific estimates had overstated the devastation caused by the asteroid, since topographic and ecologic factors contributing to the result had not been taken into account.
"There's actually less devastation than previously thought," says Boslough, "but it was caused by a far smaller asteroid. Unfortunately, it's not a complete wash in terms of the potential hazard, because there are more smaller asteroids than larger ones."
Boslough and colleagues achieved fame more than a decade ago by accurately predicting that that the fireball caused by the intersection of the comet Shoemaker-Levy 9 with Jupiter would be observable from Earth.
Simulations show that the material of an incoming asteroid is compressed by the increasing resistance of Earth's atmosphere. As it penetrates deeper, the more and more resistant atmospheric wall causes it to explode as an airburst that precipitates the downward flow of heated gas.
Because of the additional energy transported toward the surface by the fireball, what scientists had thought to be an explosion between 10 and 20 megatons was more likely only three to five megatons. The physical size of the asteroid, says Boslough, depends upon its speed and whether it is porous or nonporous, icy or waterless, and other material characteristics.
"Any strategy for defense or deflection should take into consideration this revised understanding of the mechanism of explosion," says Boslough.
One of most prominent papers in estimating frequency of impact was published five years ago in Nature by Sandia researcher Dick Spalding and his colleagues, from satellite data on explosions in atmosphere. "They can count those events and estimate frequencies of arrival through probabilistic arguments," says Boslough.
The work was presented at the American Geophysical Union meeting in San Francisco on Dec. 11. A paper on the phenomenon, co-authored by Sandia researcher Dave Crawford and entitled "Low-altitude airbursts and the impact threat" has been accepted for publication in the International Journal of Impact Engineering.
The research was paid for by Sandia's Laboratory-Directed Research and Development office.
==================================
NEW BOOK ON IMPACTS AND HUMAN SOCIETY
During the first days of December 2004, a multidisciplinary workshop was held in the town of La Laguna on the Canary isle of Tenerife with the title "Comet/Asteroid Impacts and Human Society". This was funded as part of a project with the same name by ICSU, the International Council for Science. The driving force behind the project is the realization of a need to support the development of both national and international policies regarding the impact hazard. And the direct goal of the workshop was to bring together experts on as wide a range of topics as possible with a bearing on all issues from the astronomical observations and dynamical theories to the down-to-Earth aspects of disaster planning and information chains.
The papers presented at this workshop - both keynote and research talks - have been refereed and are now available as a Springer volume entitled "Comet/Asteroid Impacts and Human Society - an Interdisciplinary Approach" (ISBN 978-3-540-32709-7), edited by Peter Bobrowsky and Hans Rickman. They were the leaders of the project and main organizers of the workshop, representing the International Union of Geological Sciences and the International Astronomical Union, respectively. The book has been prepared as a technical document describing the state of knowledge in many different fields in a way that should be understandable across all borders. It should not be perceived as the end of an effort but rather as the beginning of something new, i.e., a concerted effort to develop an interdisciplinary scientific field and bring the knowledge to both citizens and decision makers of society.
Hans Rickman
--
+++++++++++++++++++++++++++++++++++++++++++
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.
NEO News (12/19/07) Tunguska Revision & New Book
Season's greetings and best wishes for a good new year!
The main story in this edition of NEO News concerns a proposed downsizing of the energy of the 1908 Tunguska airburst, with associated increase in the expected frequency of such impacts. Mark Boslough of Sandia has generated supercomputer simulations of the Tunguska atmospheric explosion. In part his models require less energy in the explosion because he includes the substantial downward momentum of the rocky impactor, rather then modeling it as a stationary explosion. If this revision (down to an estimated energy of 3-5 megatons, and a corresponding diameter of about 50 meters) is correct, the expected frequency of such impacts changes, from once in a couple of millennia to once in a few hundred years. If smaller impactors can do the damage previously associated with larger ones, of course, the total hazard from such impacts is increased.
The second item below is an announcement of publication of a new multi-author book "Comet/Asteroid Impacts and Human Society."
David Morrison
===================================
NEW ESTIMATE OF TUNGUSKA IMPACTOR SIZE
Sandia: December 17, 2007
ALBUQUERQUE, N.M. - The stunning amount of forest devastation at Tunguska a century ago in Siberia may have been caused by an asteroid only a fraction as large as previously published estimates, Sandia National Laboratories supercomputer simulations suggest.
"The asteroid that caused the extensive damage was much smaller than we had thought," says Sandia principal investigator Mark Boslough of the impact that occurred June 30, 1908. "That such a small object can do this kind of destruction suggests that smaller asteroids are something to consider. Their smaller size indicates such collisions are not as improbable as we had believed." Because smaller asteroids approach Earth statistically more frequently than larger ones, he says, "We should be making more efforts at detecting the smaller ones than we have till now."
The new simulation -- which more closely matches the widely known facts of destruction than earlier models -- shows that the center of mass of an asteroid exploding above the ground is transported downward at speeds faster than sound. It takes the form of a high-temperature jet of expanding gas called a fireball. This causes stronger blast waves and thermal radiation pulses at the surface than would be predicted by an explosion limited to the height at which the blast was initiated.
"Our understanding was oversimplified," says Boslough, "We no longer have to make the same simplifying assumptions, because present-day supercomputers allow us to do things with high resolution in 3-D. Everything gets clearer as you look at things with more refined tools."
The new interpretation also accounts for the fact that winds were amplified above ridgelines where trees tended to be blown down, and that the forest at the time of the explosion, according to foresters, was not healthy. Thus previous scientific estimates had overstated the devastation caused by the asteroid, since topographic and ecologic factors contributing to the result had not been taken into account.
"There's actually less devastation than previously thought," says Boslough, "but it was caused by a far smaller asteroid. Unfortunately, it's not a complete wash in terms of the potential hazard, because there are more smaller asteroids than larger ones."
Boslough and colleagues achieved fame more than a decade ago by accurately predicting that that the fireball caused by the intersection of the comet Shoemaker-Levy 9 with Jupiter would be observable from Earth.
Simulations show that the material of an incoming asteroid is compressed by the increasing resistance of Earth's atmosphere. As it penetrates deeper, the more and more resistant atmospheric wall causes it to explode as an airburst that precipitates the downward flow of heated gas.
Because of the additional energy transported toward the surface by the fireball, what scientists had thought to be an explosion between 10 and 20 megatons was more likely only three to five megatons. The physical size of the asteroid, says Boslough, depends upon its speed and whether it is porous or nonporous, icy or waterless, and other material characteristics.
"Any strategy for defense or deflection should take into consideration this revised understanding of the mechanism of explosion," says Boslough.
One of most prominent papers in estimating frequency of impact was published five years ago in Nature by Sandia researcher Dick Spalding and his colleagues, from satellite data on explosions in atmosphere. "They can count those events and estimate frequencies of arrival through probabilistic arguments," says Boslough.
The work was presented at the American Geophysical Union meeting in San Francisco on Dec. 11. A paper on the phenomenon, co-authored by Sandia researcher Dave Crawford and entitled "Low-altitude airbursts and the impact threat" has been accepted for publication in the International Journal of Impact Engineering.
The research was paid for by Sandia's Laboratory-Directed Research and Development office.
==================================
NEW BOOK ON IMPACTS AND HUMAN SOCIETY
During the first days of December 2004, a multidisciplinary workshop was held in the town of La Laguna on the Canary isle of Tenerife with the title "Comet/Asteroid Impacts and Human Society". This was funded as part of a project with the same name by ICSU, the International Council for Science. The driving force behind the project is the realization of a need to support the development of both national and international policies regarding the impact hazard. And the direct goal of the workshop was to bring together experts on as wide a range of topics as possible with a bearing on all issues from the astronomical observations and dynamical theories to the down-to-Earth aspects of disaster planning and information chains.
The papers presented at this workshop - both keynote and research talks - have been refereed and are now available as a Springer volume entitled "Comet/Asteroid Impacts and Human Society - an Interdisciplinary Approach" (ISBN 978-3-540-32709-7), edited by Peter Bobrowsky and Hans Rickman. They were the leaders of the project and main organizers of the workshop, representing the International Union of Geological Sciences and the International Astronomical Union, respectively. The book has been prepared as a technical document describing the state of knowledge in many different fields in a way that should be understandable across all borders. It should not be perceived as the end of an effort but rather as the beginning of something new, i.e., a concerted effort to develop an interdisciplinary scientific field and bring the knowledge to both citizens and decision makers of society.
Hans Rickman
--
+++++++++++++++++++++++++++++++++++++++++++
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.
International Primitive Body Exploration Working Group (IPEWG): 14-16 Janaury 2008 (Okinawa, Japan)
From the conference website...
Thanks to successful development of enabling technologies for deep space exploration, missions to small solar system bodies have revolutionized our understanding of the Solar System’s origin and evolution in the last decade. At present, rendezvous, impact, landing and sample return missions to asteroids and comets such as NEAR-Shoemaker, Hayabusa, Stardust, Deep Impact, Rosetta,Dawn, EPOXI and NEXT as well as New Horizons, a fly-by mission to EKBOs, are completed or still in the middle of operation.
Also more challenging, new missions are under development or under concept studies by several space agencies including Hayabusa-2, Hayabusa Mk-II(Marco Polo), Don Quijote, OSIRIS, and Phobos-Grunt.
In addition to scientific and engineering motivations, NEO studies receive increasing interests in the context of planetary defense, deep space human spaceflight and potential in-situ resource utilization.
In 1980’s, the inter-agency coordination group for Comet Halley exploration proved that synergy of coordinated individual missions could enrich total outcomes more than each result combined.Since then, international exploration working groups participated by international space agencies have been formed and played key roles for advancing fields of solar terrestrial physics, Moon and Mars missions.
As we are entering the second golden age of the primitive body exploration in upcoming decade, now is the appropriate time to create the International Primitive Body Exploration Working Group (IPEWG) in order to promote international collaborations and to maximize outcomes of each mission. With these in mind, the first IPEWG meeting will be hosted by JAXA at Okinawa,the southern-most, tropical island in Japan. All space agencies, scientists, engineers and other interested stakeholders are cordially invited.
Session-1: Currently Operated Missions Review
(The following is a list of potential presentations)
[Asteroids]
Hayabusa
Dawn
[Comets]
Rosetta
NeXT
EPOXI
[Trans-Neptunian]
New Horizons
Session-2: Missions in Preparation & Concepts
(The following is a list of potential presentations)
[Asteroids]
Hayabusa-2
Marco Polo
OSIRIS
Phobos-Grunt
NEA Observer
Don Quijote
Small NEO Missions
Apophis Mission
NASA Human NEO
Solar Power Sail
[Comets]
Comet Surface Sample Return
Triple-F
Link: Conference Website
Thanks to successful development of enabling technologies for deep space exploration, missions to small solar system bodies have revolutionized our understanding of the Solar System’s origin and evolution in the last decade. At present, rendezvous, impact, landing and sample return missions to asteroids and comets such as NEAR-Shoemaker, Hayabusa, Stardust, Deep Impact, Rosetta,Dawn, EPOXI and NEXT as well as New Horizons, a fly-by mission to EKBOs, are completed or still in the middle of operation.
Also more challenging, new missions are under development or under concept studies by several space agencies including Hayabusa-2, Hayabusa Mk-II(Marco Polo), Don Quijote, OSIRIS, and Phobos-Grunt.
In addition to scientific and engineering motivations, NEO studies receive increasing interests in the context of planetary defense, deep space human spaceflight and potential in-situ resource utilization.
In 1980’s, the inter-agency coordination group for Comet Halley exploration proved that synergy of coordinated individual missions could enrich total outcomes more than each result combined.Since then, international exploration working groups participated by international space agencies have been formed and played key roles for advancing fields of solar terrestrial physics, Moon and Mars missions.
As we are entering the second golden age of the primitive body exploration in upcoming decade, now is the appropriate time to create the International Primitive Body Exploration Working Group (IPEWG) in order to promote international collaborations and to maximize outcomes of each mission. With these in mind, the first IPEWG meeting will be hosted by JAXA at Okinawa,the southern-most, tropical island in Japan. All space agencies, scientists, engineers and other interested stakeholders are cordially invited.
Session-1: Currently Operated Missions Review
(The following is a list of potential presentations)
[Asteroids]
Hayabusa
Dawn
[Comets]
Rosetta
NeXT
EPOXI
[Trans-Neptunian]
New Horizons
Session-2: Missions in Preparation & Concepts
(The following is a list of potential presentations)
[Asteroids]
Hayabusa-2
Marco Polo
OSIRIS
Phobos-Grunt
NEA Observer
Don Quijote
Small NEO Missions
Apophis Mission
NASA Human NEO
Solar Power Sail
[Comets]
Comet Surface Sample Return
Triple-F
Link: Conference Website
Andrei Ol'khovatov's Very Extenstive Site on Tunguska Event
Map above (taken from Yevgenii Krinov's 1949 book called "The Tunguska meteorite"), with Krinov's marks of various Tunguska manifestations
Here is a link to Andrei Ol'khovatov's site where he seems to have the latest information on the Tunguska research. Remember: next year, 30 June 2008, is the 100th anniversary of the Tunguska event.
Link: Tunguska Update
Link: Andrei Ol'khovatov's main site
Article: "Small Asteroids Pose Big New Threat"
A supercomputer simulation of a fireball that might be expected from an asteroid exploding in Earth's atmosphere, as pointed out by Sandia National Laboratories researcher Mark Boslough. Credit: Randy Montoya
From the abstract...
"Computational Modeling of Low-Altitude Airbursts," Boslough, M. [Sandia National Laboratories], American Geophysical Union 2007 Fall Meeting, San Francisco, CA, December 10-14, 2007.
New simulations of airbursts in the Earth's lower atmosphere from hypervelocity asteroid impacts suggest that a re-evaluation of the impact hazard is necessary to properly account for the enhanced damage potential relative to point-source approximations. The intent of these simulations was to explore the phenomenology associated with low-altitude airbursts and to determine whether the altitude of maximum energy deposition can be used as a reasonable estimate of the equivalent height of a point explosion. The simulations suggest that this not a good approximation, because the center of mass of an exploding projectile is transported downward in the form of a high-temperature jet of expanding gas. The jet descends by a significant fraction of the burst altitude before its velocity becomes subsonic. The time scale of this descent is similar to the time scale of the explosion itself, so the jet simultaneously couples both its translational and its radial kinetic energy to the atmosphere. Because of this downward flow, larger blast waves and stronger thermal radiation pulses are felt at the surface than would be predicted for a nuclear explosion of the same yield at the same height. For impacts with a kinetic energy above some threshold, the hot jet of vaporized projectile (the descending "fireball") makes contact with the Earth's surface, where it expands radially. During the time of radial expansion, the fireball can maintain temperatures well above the melting temperature of silicate minerals, and its radial velocity can exceed the sound speed in air. Surface materials can ablate by radiative/convective melting under these conditions, and then quench rapidly to form glass after the fireball cools and recedes. One possible example of an airburst glass is the Libyan Desert Glass of western Egypt. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000.
From the article...
Now new supercomputer simulations suggest "the asteroid that caused the extensive damage was much smaller than we had thought," Boslough [Mark Boslough, a physicist at Sandia National Laboratory in Albuquerque, N.M.] said. Specifically, he and his colleagues say it would have been a factor of three or four smaller in mass and perhaps 65 feet (20 meters) in diameter.
The simulations run on Sandia's Red Storm supercomputer — the third fastest in the world — detail how an asteroid that explodes as it runs into Earth's atmosphere will generate a supersonic jet of expanding superheated gas. This fireball would have caused blast waves that were stronger at the surface than previously thought.
At the same time, previous estimates seem to have overstated the devastation the event caused. The forest back then was not healthy, according to foresters, "and it doesn't take as much energy to blow down a diseased tree than a healthy tree," Boslough said. In addition, the winds from the explosion would naturally get amplified above ridgelines, making the explosion seem more powerful than it actually was. What scientists had thought to be an explosion between 10 and 20 megatons was more likely only three to five megatons, he explained.
All in all, the researchers suggest that smaller asteroids may pose a greater danger than previously believed. Moreover, "there are a lot more objects that size," Boslough told SPACE.com.
NASA Ames Research Center planetary scientist and astrobiologist David Morrison, who did not participate in this study, said, "If he's right, we can expect more Tunguska-sized explosions — perhaps every couple of centuries instead of every millennia or two." He added, "It raises the bar in the long term — ultimately, we'd like to have a survey system that can detect things this small."
Boslough and his colleagues detailed their findings at the American Geophysical Union meeting in San Francisco on Dec. 11. A paper on the phenomenon has been accepted for publication in the International Journal of Impact Engineering.
"Small Asteroids Pose Big New Threat"
Charles Q. Choi
19 December 2007
SPACE.com
Link: Space.com Article
"Computational Modeling of Low-Altitude Airbursts," Boslough, M. [Sandia National Laboratories], American Geophysical Union 2007 Fall Meeting, San Francisco, CA, December 10-14, 2007.
"Terrestrial Impact Cratering: New Insights Into the Cratering Process From Geophysics and Geochemistry," C. Koeberl [University of Vienna], M. Boslough [Sandia National Laboratories], American Geophysical Union 2007 Fall Meeting, San Francisco, CA, December 10-14, 2007.
Link: American Geophysical Union 2007 Fall Meeting
18 December 2007
U.S. Congress to Have National Research Council Review Arecibo and NASA NEO Report
Looks as if there may be a National Research Council (NRC) review of decisions regarding Arecibo (and any closure of it) as well as the recent NASA NEO Study. From the recent US Omnibus Congressional Legislation for the FY2008 US Budget:
"In order to assist Congress in determining the optimal approach regarding the Arecibo Observatory, NASA shall contract with the National Research Council to study the issue and make recommendations. As part of its deliberations, the NRC shall review NASA's report 2006 Near-Earth Object Survey and Deflection Study - and its associated March 2007 Near-Earth Object Survey and Deflection Study as well as any other relevant literature. An interim report, with recommendations focusing primarily on the optimal approach to the survey program, shall be submitted within 15 months of enactment of this Act. The final report, including recommendations regarding the optimal approach to developing a deflection capability, shall be submitted within 21 months of enactment of this Act. The NRC study shall include an assessment of the costs of various alternatives, including options that may blend the use of different facilities (whether ground- or space-based), or involve international cooperation. Independent cost estimating should be utilized."
Link: Text of the House Amendments to Senate Amendment to H.R. 2764 – State, Foreign Operations, and Related Programs Appropriations Act, 2008 (Consolidated Appropriations Act, 2008) Division B--Commerce, Justice, Science
"In order to assist Congress in determining the optimal approach regarding the Arecibo Observatory, NASA shall contract with the National Research Council to study the issue and make recommendations. As part of its deliberations, the NRC shall review NASA's report 2006 Near-Earth Object Survey and Deflection Study - and its associated March 2007 Near-Earth Object Survey and Deflection Study as well as any other relevant literature. An interim report, with recommendations focusing primarily on the optimal approach to the survey program, shall be submitted within 15 months of enactment of this Act. The final report, including recommendations regarding the optimal approach to developing a deflection capability, shall be submitted within 21 months of enactment of this Act. The NRC study shall include an assessment of the costs of various alternatives, including options that may blend the use of different facilities (whether ground- or space-based), or involve international cooperation. Independent cost estimating should be utilized."
Link: Text of the House Amendments to Senate Amendment to H.R. 2764 – State, Foreign Operations, and Related Programs Appropriations Act, 2008 (Consolidated Appropriations Act, 2008) Division B--Commerce, Justice, Science
16 December 2007
Non-Asteroid Related: Mars Surface Habitat Video
This is not related specifically to planetary defense but to my job. From the news announcement:
SpaceWorks Engineering, Inc. (SEI) announces it has produced a new video entitled "Mars Vision: The Surface", a visualization of human exploration on the surface of Mars. This video shows the interior of a habitat where future explorers would reside during surface operations. The depicted concept is based upon a human exploration architecture for Mars designed independently in 2007 by SpaceWorks Engineering, Inc. (SEI). The lead technical author of this concept is Dr. Brad St. Germain, Director of the Advanced Concepts Group (ACG) at SEI. "Mars Vision: The Surface" video developer and SEI lead concept artist is Mr. Mark Elwood. The video is available on YouTube; please see the "SpaceWorksEng" user on YouTube. The video is also available for direct download from the links below. A technical paper is also available that describes a related notional Mars architecture as developed by SEI.
Link: SEI News Announcement
Link: "Mars Vision: The Surface" Video: YouTube
Link: "Mars Vision: The Surface" Video: Direct Download - MPEG4 (47.1 MB)
Link: "Mars Vision: The Surface" Video: Direct Download - MPEG2 (85 MB)
Link: "Mars Vision: The Surface" Video: Direct Download - AVI (42.6 MB)
SpaceWorks Engineering, Inc. (SEI) announces it has produced a new video entitled "Mars Vision: The Surface", a visualization of human exploration on the surface of Mars. This video shows the interior of a habitat where future explorers would reside during surface operations. The depicted concept is based upon a human exploration architecture for Mars designed independently in 2007 by SpaceWorks Engineering, Inc. (SEI). The lead technical author of this concept is Dr. Brad St. Germain, Director of the Advanced Concepts Group (ACG) at SEI. "Mars Vision: The Surface" video developer and SEI lead concept artist is Mr. Mark Elwood. The video is available on YouTube; please see the "SpaceWorksEng" user on YouTube. The video is also available for direct download from the links below. A technical paper is also available that describes a related notional Mars architecture as developed by SEI.
Link: SEI News Announcement
Link: "Mars Vision: The Surface" Video: YouTube
Link: "Mars Vision: The Surface" Video: Direct Download - MPEG4 (47.1 MB)
Link: "Mars Vision: The Surface" Video: Direct Download - MPEG2 (85 MB)
Link: "Mars Vision: The Surface" Video: Direct Download - AVI (42.6 MB)
14 December 2007
NASA does not select OSIRIS asteroid sample return mission for selection as Discovery Mission
From the article:
The University of Arizona has lost out on $425 million in NASA funding after the space agency selected a competing proposal for its next Discovery Class mission.
The UA's OSIRIS mission, which would have launched a spacecraft to collect and return material from a near-Earth asteroid, was one of three finalists competing for the NASA funding. NASA officials announced this week that another finalist, a moon mission known as GRAIL, will move forward.
"It was a bit of a shock, frankly," said Michael Drake, director of the UA's Lunar and Planetary Laboratory and principal investigator for OSIRIS.
The lab will continue to seek funding for the asteroid-sample-return mission, modifying the proposal based on feedback from NASA officials. The ongoing Discovery program aims to launch a mission every 12 to 24 months.
Link: Article
"NASA turns down UA asteroid plan Proposal to collect, return material was one of three project finalists
Eric Swedlund
Arizona Daily Star
14 December 2007
Link: NASA Discovery Program announcement about the lunar Gravity Recovery and Interior Laboratory (GRAIL) mission
The University of Arizona has lost out on $425 million in NASA funding after the space agency selected a competing proposal for its next Discovery Class mission.
The UA's OSIRIS mission, which would have launched a spacecraft to collect and return material from a near-Earth asteroid, was one of three finalists competing for the NASA funding. NASA officials announced this week that another finalist, a moon mission known as GRAIL, will move forward.
"It was a bit of a shock, frankly," said Michael Drake, director of the UA's Lunar and Planetary Laboratory and principal investigator for OSIRIS.
The lab will continue to seek funding for the asteroid-sample-return mission, modifying the proposal based on feedback from NASA officials. The ongoing Discovery program aims to launch a mission every 12 to 24 months.
Link: Article
"NASA turns down UA asteroid plan Proposal to collect, return material was one of three project finalists
Eric Swedlund
Arizona Daily Star
14 December 2007
Link: NASA Discovery Program announcement about the lunar Gravity Recovery and Interior Laboratory (GRAIL) mission
10 December 2007
Update on Results for Planetary Society's Apophis Mission Design Competition
I talked to Bruce Betts, Director of Projects for the Planetary Society, at the recent Space Investment Summit (SIS) 3 in San Jose, California. He said that the judging of their Apophis Mission Design Competition is taking a little longer. Whereas the original schedule called for winners to be announced in the middle of December, he stated that the current plan calls for an announcement in January 2008.
Article: "Practice run [to asteroid] before Mars suggested"
From the article:
"A near-Earth asteroid is a great intermediate destination that would allow NASA to check out the launch systems and crew vehicles, as well as set procedures," Huntress [former NASA associate administrator for science] told a group of about 100 people at the U.S. Space & Rocket Center. "It would be a six-month, or even a year mission, but that's quick compared to a three-year or longer human voyage to Mars...In the end it would give NASA confidence to go to another planet."
"Practice run before Mars suggested"
08 December 2007
Huntsville Times
Shelby G. Spires
Link: Article
"A near-Earth asteroid is a great intermediate destination that would allow NASA to check out the launch systems and crew vehicles, as well as set procedures," Huntress [former NASA associate administrator for science] told a group of about 100 people at the U.S. Space & Rocket Center. "It would be a six-month, or even a year mission, but that's quick compared to a three-year or longer human voyage to Mars...In the end it would give NASA confidence to go to another planet."
"Practice run before Mars suggested"
08 December 2007
Huntsville Times
Shelby G. Spires
Link: Article
Article: "The Best Way to Deflect an Asteroid"
From the article:
Massimiliano Vasile, a lecturer in aerospace engineering at the University of Glasgow, recently concluded a two-year study comparing nine asteroid-deflection methods, rating them for efficiency, complexity and launch readiness.
The best method, called “mirror bees,” entails sending a group of small satellites equipped with mirrors 30 to 100 feet wide into space to “swarm” around an asteroid and trail it, Vasile explains. The mirrors would be tilted to reflect sunlight onto the asteroid, vaporizing one spot and releasing a stream of gases that would slowly move it off course. Vasile says this method is especially appealing because it could be scaled easily: 25 to 5,000 satellites could be used, depending on the size of the rock.
The losing ideas — satellites equipped with lasers; detonating a nuclear explosion; pushing the asteroid with a spacecraft, to name a few — might still have their place. Vasile says improved technologies could make others appealing in the future. (In March, NASA released a report on “near Earth objects” that deemed the nuclear-explosion method the most effective.)
"The Best Way to Deflect an Asteroid"
New York Times
Lia Miller
09 December 2007
Link: Article
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