21 April 2008
Animation of Foresight: A Radio Beacon Mission to Asteroid Apophis
SpaceWorks Engineering, Inc. (SEI) has produced a new animation of the Foresight mission, a radio beacon mission to Near Earth Asteroid Apophis. This was our team's first place design in the recent Planetary Society Apophis Mission Design Competition. Our partner in the design was SpaceDev, Inc. We have placed the animation on YouTube and it is also available for high resolution download from the SpaceWorks website.
Link: YouTube
Link: SEI News Announcement
19 April 2008
The Planetary Society Article on Tunguska
Selections from the article...
Boslough and Crawford [Mark Boslough and David Crawford of the Sandia National Laboratories in New Mexico] ran repeated simulations of the Tunguska event [for an rticle forthcoming in the International Journal of Impact Engineering], trying to reproduce the scale of the devastation seen in the region. From this they concluded that even if the airburst explosion took place at an altitude of 12 kilometers or higher, it probably had a magnitude of only 3 to 5 megatons. This is considerable less than the popular figure of 10 to 15 megatons, and less than 1% the high end suggestion of 700 megatons. That such a comparatively small explosion could cause this much damage is due to the fact that it was not a point explosion at the airburst altitude that caused the damage, but the fireball and shockwave that continued moving towards the surface. At a height of around 4 kilometers, the simulations show, the fireball came to a stop, but the shockwave continued on. It was the shockwave, not the explosion at the airburst altitude and not even the streaking fireball, which was responsible for most of the devastation in the forest.
"The Tunguska Riddle: How Powerful was the Greatest Asteroid Impact in Recorded History?"
Amir Alexander
The Planetary Society
15 April 2008
Link: Article from The Planetary Society
----------
Other previous article by Mark Boslough on impact assessment and modeling (from the International Journal of Impact Engineering).
Axial focusing of energy from a hypervelocity impact on earth
International Journal of Impact Engineering, Volume 17, Issues 1-3, 1995, Pages 99-108
M. B. Boslough, E. P. Chael, T. G. Trucano, D. A. Crawford
The impact of periodic comet shoemaker-levy 9 on jupiter
International Journal of Impact Engineering, Volume 17, Issues 1-3, 1995, Pages 253-262
D. A. Crawford, M. B. Boslough, T. G. Trucano, A. C. Robinson
Dynamical properties measurements for asteroid, comet and meteorite material applicable to impact modeling and mitigation calculations
International Journal of Impact Engineering, Volume 17, Issues 1-3, 1995, Pages 341-352
M. D. Furnish, M. B. Boslough, G. T. Gray III, J. L. Remo
Hypervelocity testing of advanced shielding concepts for spacecraft against impacts to 10 km/s
International Journal of Impact Engineering, Volume 14, Issues 1-4, 1993, Pages 95-106
M. B. Boslough, J. A. Ang, L. C. Chhabildas, W. D. Reinhart, C. A. Hall, B. G. Cour-Palais, E. L. Christiansen, J. L. Crews
Shock-induced solid-state chemical reactivity studies using time-resolved radiation pyrometry
International Journal of Impact Engineering, Volume 5, Issues 1-4, 1987, Pages 173-180
M. B. Boslough
Boslough and Crawford [Mark Boslough and David Crawford of the Sandia National Laboratories in New Mexico] ran repeated simulations of the Tunguska event [for an rticle forthcoming in the International Journal of Impact Engineering], trying to reproduce the scale of the devastation seen in the region. From this they concluded that even if the airburst explosion took place at an altitude of 12 kilometers or higher, it probably had a magnitude of only 3 to 5 megatons. This is considerable less than the popular figure of 10 to 15 megatons, and less than 1% the high end suggestion of 700 megatons. That such a comparatively small explosion could cause this much damage is due to the fact that it was not a point explosion at the airburst altitude that caused the damage, but the fireball and shockwave that continued moving towards the surface. At a height of around 4 kilometers, the simulations show, the fireball came to a stop, but the shockwave continued on. It was the shockwave, not the explosion at the airburst altitude and not even the streaking fireball, which was responsible for most of the devastation in the forest.
"The Tunguska Riddle: How Powerful was the Greatest Asteroid Impact in Recorded History?"
Amir Alexander
The Planetary Society
15 April 2008
Link: Article from The Planetary Society
----------
Other previous article by Mark Boslough on impact assessment and modeling (from the International Journal of Impact Engineering).
Axial focusing of energy from a hypervelocity impact on earth
International Journal of Impact Engineering, Volume 17, Issues 1-3, 1995, Pages 99-108
M. B. Boslough, E. P. Chael, T. G. Trucano, D. A. Crawford
The impact of periodic comet shoemaker-levy 9 on jupiter
International Journal of Impact Engineering, Volume 17, Issues 1-3, 1995, Pages 253-262
D. A. Crawford, M. B. Boslough, T. G. Trucano, A. C. Robinson
Dynamical properties measurements for asteroid, comet and meteorite material applicable to impact modeling and mitigation calculations
International Journal of Impact Engineering, Volume 17, Issues 1-3, 1995, Pages 341-352
M. D. Furnish, M. B. Boslough, G. T. Gray III, J. L. Remo
Hypervelocity testing of advanced shielding concepts for spacecraft against impacts to 10 km/s
International Journal of Impact Engineering, Volume 14, Issues 1-4, 1993, Pages 95-106
M. B. Boslough, J. A. Ang, L. C. Chhabildas, W. D. Reinhart, C. A. Hall, B. G. Cour-Palais, E. L. Christiansen, J. L. Crews
Shock-induced solid-state chemical reactivity studies using time-resolved radiation pyrometry
International Journal of Impact Engineering, Volume 5, Issues 1-4, 1987, Pages 173-180
M. B. Boslough
16 April 2008
Correcting Media Sensationalism on Apophis, 13 year old kid, and NASA
Ok. Not True. Here is the history's judgment on this media blow up over a 13 year old's prediction that Apophis has a 1 in 450 chance of hitting the Earth in 2036 (not true, actually it is 1 in 45,000). Here is NASA's statement and Daniel Fischer's blog entry explaining the situation.
----------
From Don Yeomans at NASA JPL NEO Site...
16 April 2008:
In response to inquiries, accidental impact with an artificial satellite in 2029 is vanishingly unlikely. As mentioned above, (1) Apophis does not pass near the zones where most satellites are located and (2) man-made satellites and Apophis both have small cross-sectional areas. Even if a high-velocity impact occurred, a large satellite could change Apophis' position 7 years later (in 2036) by only 100's of km at most. This is less than 1/10th the size of the smallest issues considered in the paper, very much in the noise of the calculations, and can have no meaningful effect on Earth impact probability estimation (which already incorporates more than 30 million km of uncertainty). At such a late date, impact with an artificial satellite would be like a bug on the windshield of Apophis. Deflection efforts are dependent on being early enough to leverage the dynamics of the 2029 encounter. Events during the encounter lack such leverage.
Link: JPL NEO Page on Apophis
----------
NASA Statement on Student Asteroid Calculations
16 April 2008
WASHINGTON -- The Near-Earth Object Program Office at NASA's Jet Propulsion Laboratory in Pasadena, Calif., has not changed its current estimates for the very low probability (1 in 45,000) of an Earth impact by the asteroid Apophis in 2036.
Contrary to recent press reports, NASA offices involved in near-Earth object research were not contacted and have had no correspondence with a young German student, who claims the Apophis impact probability is far higher than the current estimate.
This student's conclusion reportedly is based on the possibility of a collision with an artificial satellite during the asteroid's close approach in April 2029. However, the asteroid will not pass near the main belt of geosynchronous satellites in 2029, and the chance of a collision with a satellite is exceedingly remote.
Therefore, consideration of this satellite collision scenario does not affect the current impact probability estimate for Apophis, which remains at 1 in 45,000.
Link: NASA Statement
----------
"Apophis risk not increased: science fair judges, world media screw up big time"
16 April 2008
First the story appeared on April 4 in Germany's 'leading' tabloid ("I have calculated the end of the world ... and NASA says, I'm right"), later in more serious papers ("Nico and the end of the world") - and today, thanks apparently to an AFP story where the writer hadn't found it necessary to check anything, it has taken off around the world. Alas: it's absolute nonsense! The claim is that a 13-year old German schoolboy "discovered" - while working on an entry for a major German science competition - that the 2036 impact probability of asteroid Apophis is not 1:45,000 as the NASA calculation says but actually 100 times higher. Because during the 2029 approach the asteroid would hit a geostationary satellite and be deflected into a much more dangerous orbit. The newspapers also claimed that this boy not only was awarded several prizes for his paper but that NASA had "conceded" that he got it right and they were wrong. We're all doomed, right?
Well, here's what NASA's NEO guru Don Yeomans told this blog yesterday: "We have not corresponded with this young man and this story is absurd, a hoax or both. During its 2029 Earth close approach, Apophis will approach the Earth to about 38,900 km, well inside the geosynchronous distance at 42,240 km. However, the asteroid will cross the equatorial belt at a distance of 51,000 km - well outside the geosynchronous distance. Since the uncertainty on Apophis' position during the Earth close approach is about 1500 km, Apophis cannot approach an Earth satellite. Apophis will not cross the moon's orbital plane at the Moon's orbital distance so it cannot approach the moon either."
And here's how one of the German scientists mentioned in the first story, celestial dynamics expert Frank Spahn from Potsdam University, explained events to this blog today: "I indeed had contact with this engaged boy - he asked me which perturbations/forces determine Apophis' orbit and especially during the close flybys. You know that I deal with kinetic theory & celestial mech. in the context of planetary rings, preplanetary disks etc. I explained him the 3 and 4 body problem and gravitational interactions in general. He did not tell me about his idea to consider a collision. This was in January or February. The next time when I heard of him was in in the boulevard journaillie "Bild" - together with my name.
I asked him to meet me (last Friday), he told me about the asteroid - satellite collision thing (after I asked him how he calculated and "corrected" the NASA result). Then I showed him at the black board about the extremely small collision probability (frequency) with such an object. Seeing the arising problems I attended the set of [German TV news station] N24 and explained the leading responsible person that I appreciate the engagement of that young student but simultaneously I express that one has to mention the low probability of such a collision plus expressing that this is not a correction to NASA. The filming session went on and I had to leave for another meeting. The I saw yesterday that nonsens in TV - and I am shocked. By the way - I haven't seen that paper and the work sofar, Nico told me that his computer disk had a virus so that only hard copies are available which are with the referees of the contest at the moment. So - I do not know how he could have won the competition, obviously the referees were no experts."
Nor were the writers for the German newspapers or AFP - none of which bothered to ask NASA directly or just consult the impact risk page for Apophis. This is clearly the most used and abused Near Earth Asteroid in many years: Still called 2004 MN4 it briefly reached a record high impact probability for 2029 in late 2004 which quickly evaporated (as always in these cases - so far) when radar data nailed down its orbit in early 2005. And in the following months the remaining impact probability for 2036 also continued to dwindle, to the present 1 in 45,000: You can follow the real science - and the triumph of radar astrometry - on this dedicated NASA website. Which certain Jugend Forscht judges and journalists should have consulted, too ...
Link: Daniel Fischer's Blog Entry
----------
From Don Yeomans at NASA JPL NEO Site...
16 April 2008:
In response to inquiries, accidental impact with an artificial satellite in 2029 is vanishingly unlikely. As mentioned above, (1) Apophis does not pass near the zones where most satellites are located and (2) man-made satellites and Apophis both have small cross-sectional areas. Even if a high-velocity impact occurred, a large satellite could change Apophis' position 7 years later (in 2036) by only 100's of km at most. This is less than 1/10th the size of the smallest issues considered in the paper, very much in the noise of the calculations, and can have no meaningful effect on Earth impact probability estimation (which already incorporates more than 30 million km of uncertainty). At such a late date, impact with an artificial satellite would be like a bug on the windshield of Apophis. Deflection efforts are dependent on being early enough to leverage the dynamics of the 2029 encounter. Events during the encounter lack such leverage.
Link: JPL NEO Page on Apophis
----------
NASA Statement on Student Asteroid Calculations
16 April 2008
WASHINGTON -- The Near-Earth Object Program Office at NASA's Jet Propulsion Laboratory in Pasadena, Calif., has not changed its current estimates for the very low probability (1 in 45,000) of an Earth impact by the asteroid Apophis in 2036.
Contrary to recent press reports, NASA offices involved in near-Earth object research were not contacted and have had no correspondence with a young German student, who claims the Apophis impact probability is far higher than the current estimate.
This student's conclusion reportedly is based on the possibility of a collision with an artificial satellite during the asteroid's close approach in April 2029. However, the asteroid will not pass near the main belt of geosynchronous satellites in 2029, and the chance of a collision with a satellite is exceedingly remote.
Therefore, consideration of this satellite collision scenario does not affect the current impact probability estimate for Apophis, which remains at 1 in 45,000.
Link: NASA Statement
----------
"Apophis risk not increased: science fair judges, world media screw up big time"
16 April 2008
First the story appeared on April 4 in Germany's 'leading' tabloid ("I have calculated the end of the world ... and NASA says, I'm right"), later in more serious papers ("Nico and the end of the world") - and today, thanks apparently to an AFP story where the writer hadn't found it necessary to check anything, it has taken off around the world. Alas: it's absolute nonsense! The claim is that a 13-year old German schoolboy "discovered" - while working on an entry for a major German science competition - that the 2036 impact probability of asteroid Apophis is not 1:45,000 as the NASA calculation says but actually 100 times higher. Because during the 2029 approach the asteroid would hit a geostationary satellite and be deflected into a much more dangerous orbit. The newspapers also claimed that this boy not only was awarded several prizes for his paper but that NASA had "conceded" that he got it right and they were wrong. We're all doomed, right?
Well, here's what NASA's NEO guru Don Yeomans told this blog yesterday: "We have not corresponded with this young man and this story is absurd, a hoax or both. During its 2029 Earth close approach, Apophis will approach the Earth to about 38,900 km, well inside the geosynchronous distance at 42,240 km. However, the asteroid will cross the equatorial belt at a distance of 51,000 km - well outside the geosynchronous distance. Since the uncertainty on Apophis' position during the Earth close approach is about 1500 km, Apophis cannot approach an Earth satellite. Apophis will not cross the moon's orbital plane at the Moon's orbital distance so it cannot approach the moon either."
And here's how one of the German scientists mentioned in the first story, celestial dynamics expert Frank Spahn from Potsdam University, explained events to this blog today: "I indeed had contact with this engaged boy - he asked me which perturbations/forces determine Apophis' orbit and especially during the close flybys. You know that I deal with kinetic theory & celestial mech. in the context of planetary rings, preplanetary disks etc. I explained him the 3 and 4 body problem and gravitational interactions in general. He did not tell me about his idea to consider a collision. This was in January or February. The next time when I heard of him was in in the boulevard journaillie "Bild" - together with my name.
I asked him to meet me (last Friday), he told me about the asteroid - satellite collision thing (after I asked him how he calculated and "corrected" the NASA result). Then I showed him at the black board about the extremely small collision probability (frequency) with such an object. Seeing the arising problems I attended the set of [German TV news station] N24 and explained the leading responsible person that I appreciate the engagement of that young student but simultaneously I express that one has to mention the low probability of such a collision plus expressing that this is not a correction to NASA. The filming session went on and I had to leave for another meeting. The I saw yesterday that nonsens in TV - and I am shocked. By the way - I haven't seen that paper and the work sofar, Nico told me that his computer disk had a virus so that only hard copies are available which are with the referees of the contest at the moment. So - I do not know how he could have won the competition, obviously the referees were no experts."
Nor were the writers for the German newspapers or AFP - none of which bothered to ask NASA directly or just consult the impact risk page for Apophis. This is clearly the most used and abused Near Earth Asteroid in many years: Still called 2004 MN4 it briefly reached a record high impact probability for 2029 in late 2004 which quickly evaporated (as always in these cases - so far) when radar data nailed down its orbit in early 2005. And in the following months the remaining impact probability for 2036 also continued to dwindle, to the present 1 in 45,000: You can follow the real science - and the triumph of radar astrometry - on this dedicated NASA website. Which certain Jugend Forscht judges and journalists should have consulted, too ...
Link: Daniel Fischer's Blog Entry
Update on Nico Marquardt (13 year old saying 1 in 450 chance of Apophis hitting the Earth in 2036)
Student Nico Marquardt (13) from Potsdam holds a lump iron in his hand. In the background, the "3-body formula," with the convergence of asteroids.
Ok. Some updates on this story. It looks like more media are picking up this story all over the world. Some articles are actually getting scientific commentators to back up the story in some ways. I have found the German article that talks about this and have provided a translation link from Goggle below.
Link: Original German Article on Nico Marquardt
Link: Translated German Article on Nico Marquardt
15 April 2008
Apophis Impact Probability is 1 in 450 instead of 1 in 45,000 (13 year old to NASA)
I do not know what to make of this article from AFP. I cannot understand their logic (are they suggesting that the chance of Apophis hitting the Earth or a satellite is 1 in 450?). Apparently the wikipedia entry for Apophis has also been updated to reflect this. I will attempt to follow the story. Here is the complete article...
German schoolboy, 13, corrects NASA's asteroid figures: paper
15 April 2008
~ 6:34 pm Eastern U.S.
BERLIN (AFP) — A 13-year-old German schoolboy corrected NASA's estimates on the chances of an asteroid colliding with Earth, a German newspaper reported Tuesday, after spotting the boffins had miscalculated.
Nico Marquardt used telescopic findings from the Institute of Astrophysics in Potsdam (AIP) to calculate that there was a 1 in 450 chance that the Apophis asteroid will collide with Earth, the Potsdamer Neuerster Nachrichten reported.
NASA had previously estimated the chances at only 1 in 45,000 but told its sister organisation, the European Space Agency (ESA), that the young whizzkid had got it right.
The schoolboy took into consideration the risk of Apophis running into one or more of the 40,000 satellites orbiting Earth during its path close to the planet on April 13 2029.
Those satellites travel at 3.07 kilometres a second (1.9 miles), at up to 35,880 kilometres above earth -- and the Apophis asteroid will pass by earth at a distance of 32,500 kilometres.
If the asteroid strikes a satellite in 2029, that will change its trajectory making it hit earth on its next orbit in 2036.
Both NASA and Marquardt agree that if the asteroid does collide with earth, it will create a ball of iron and iridium 320 metres (1049 feet) wide and weighing 200 billion tonnes, which will crash into the Atlantic Ocean.
The shockwaves from that would create huge tsunami waves, destroying both coastlines and inland areas, whilst creating a thick cloud of dust that would darken the skies indefinitely.
The 13-year old made his discovery as part of a regional science competition for which he submitted a project entitled: "Apophis -- The Killer Astroid."
"German schoolboy, 13, corrects NASA's asteroid figures: paper"
15 April 2008
Link: AFP Article
German schoolboy, 13, corrects NASA's asteroid figures: paper
15 April 2008
~ 6:34 pm Eastern U.S.
BERLIN (AFP) — A 13-year-old German schoolboy corrected NASA's estimates on the chances of an asteroid colliding with Earth, a German newspaper reported Tuesday, after spotting the boffins had miscalculated.
Nico Marquardt used telescopic findings from the Institute of Astrophysics in Potsdam (AIP) to calculate that there was a 1 in 450 chance that the Apophis asteroid will collide with Earth, the Potsdamer Neuerster Nachrichten reported.
NASA had previously estimated the chances at only 1 in 45,000 but told its sister organisation, the European Space Agency (ESA), that the young whizzkid had got it right.
The schoolboy took into consideration the risk of Apophis running into one or more of the 40,000 satellites orbiting Earth during its path close to the planet on April 13 2029.
Those satellites travel at 3.07 kilometres a second (1.9 miles), at up to 35,880 kilometres above earth -- and the Apophis asteroid will pass by earth at a distance of 32,500 kilometres.
If the asteroid strikes a satellite in 2029, that will change its trajectory making it hit earth on its next orbit in 2036.
Both NASA and Marquardt agree that if the asteroid does collide with earth, it will create a ball of iron and iridium 320 metres (1049 feet) wide and weighing 200 billion tonnes, which will crash into the Atlantic Ocean.
The shockwaves from that would create huge tsunami waves, destroying both coastlines and inland areas, whilst creating a thick cloud of dust that would darken the skies indefinitely.
The 13-year old made his discovery as part of a regional science competition for which he submitted a project entitled: "Apophis -- The Killer Astroid."
"German schoolboy, 13, corrects NASA's asteroid figures: paper"
15 April 2008
Link: AFP Article
14 April 2008
Update on Hayabusa (From Don Yeomans at JPL)
Selections from the article...
Even if Japan's problem-plagued Hayabusa spacecraft makes it back to Earth as planned in 2010, a pointing problem may prevent it from dropping a capsule – which may contain asteroid dust – safely to Earth. Instead, it may send the capsule careening off into space, or hurtling to a fiery death in Earth's atmosphere, mission members say.
Hayabusa was meant to collect samples from the asteroid Itokawa by firing pellets into the surface of the 535-metre-long rock and scooping up the resulting debris. But data from two landings in November 2005 suggest the pellets never fired because the craft's onboard computer sent conflicting signals to its collection instruments.
Still, mission officials hoped to bring the spacecraft back to Earth in case some asteroid dust had slipped into its collection chamber by chance. If it completes the trip, it is expected to drop a capsule in the Australian outback in June 2010.
But even if it makes it back to Earth, the spacecraft might not be able to point itself in the right direction to land the capsule safely, says mission team member Don Yeomans of NASA's Jet Propulsion Laboratory in Pasadena, California, US.
"I get the sense from our Japanese colleagues that it's not a sure thing they'll get the capsule back to Australia," Yeomans told New Scientist. That's because Hayabusa is crippled by the loss of fuel used to point itself and of two of its three stabilising gyroscopes, problems that occurred in 2005.
"Crippled probe may send cargo drifting into space"
Elise Kleeman
NewScientist.com
14 April 2008
Link: NewScientist Article
Even if Japan's problem-plagued Hayabusa spacecraft makes it back to Earth as planned in 2010, a pointing problem may prevent it from dropping a capsule – which may contain asteroid dust – safely to Earth. Instead, it may send the capsule careening off into space, or hurtling to a fiery death in Earth's atmosphere, mission members say.
Hayabusa was meant to collect samples from the asteroid Itokawa by firing pellets into the surface of the 535-metre-long rock and scooping up the resulting debris. But data from two landings in November 2005 suggest the pellets never fired because the craft's onboard computer sent conflicting signals to its collection instruments.
Still, mission officials hoped to bring the spacecraft back to Earth in case some asteroid dust had slipped into its collection chamber by chance. If it completes the trip, it is expected to drop a capsule in the Australian outback in June 2010.
But even if it makes it back to Earth, the spacecraft might not be able to point itself in the right direction to land the capsule safely, says mission team member Don Yeomans of NASA's Jet Propulsion Laboratory in Pasadena, California, US.
"I get the sense from our Japanese colleagues that it's not a sure thing they'll get the capsule back to Australia," Yeomans told New Scientist. That's because Hayabusa is crippled by the loss of fuel used to point itself and of two of its three stabilising gyroscopes, problems that occurred in 2005.
"Crippled probe may send cargo drifting into space"
Elise Kleeman
NewScientist.com
14 April 2008
Link: NewScientist Article
13 April 2008
New Article in Geology on Chesapeake Bay Impact (1 - 1.5 miles in diameter, about 35 million years ago)
Selections from the article...
A Western Michigan University graduate student is the lead author of an article in the April issue of Geology magazine that explores how the crust of the Earth behaves after being hit by a comet or asteroid and could shed light on how the moon's surface was formed.
Travis Hayden, a graduate student in geosciences from Portage, Mich., is among seven authors who contributed to the article, titled "Impact effects and regional tectonic insights: Backstripping the Chesapeake Bay impact structure." Hayden's main advisor, Dr. Michelle Kominz, a WMU professor of geosciences, also contributed to the article.
Published by the Geological Society of America, Geology is one of the most popular and widely read earth science journals in print, with 20 or more thought-provoking articles each month. The article written by Hayden, Kominz and five other scientists examined the impact of an object, probably a comet or asteroid, that struck the Earth in the Chesapeake Bay area. The object was 1 to 1.5 miles in diameter and hit the Earth about 35 million years ago, Hayden says.
It was widely thought that such an impact would have long-lasting effects on the Earth's crust. In addition to forming a very large crater, scientists believed a significant amount of heat would have been generated in such a strike, melting a portion of the Earth's crust.
"The interesting thing was that we found it behaved exactly the opposite of what everybody expected," Hayden says. "Everyone had assumed that the impact released a whole bunch of heat, melted a lot of rocks and this heat actually changed how the crust behaves over time." Hayden says the impact did generate a lot of heat and melted a lot of rock, but most of the molten debris was thrown out of the crater. All the material that then filled in the crater afterward wasn't hot at all--it was cold.
And that affected what happened to the crust, Hayden says. Scientists had believed an impact and resulting melting of rock in the crater would have resulted in uplift within the crater followed by subsidence. Their results showed just the opposite happened. The crust subsided about 100 meters, and that was followed by uplift. "This was out of left field," Hayden says.
The results help to better understand how such impacts affect the crusts of the Earth and other bodies, including the moon, Hayden says.
"The seas of the moon, such as the Sea of Tranquility, are thought to be formed by this kind of melt, when a big impact came in, melted a whole lot of rock and then kind of paved everything out pretty smoothly" Hayden says. "But no one had been able to test it. So this was the first time we've ever been able to look at it in the real world to see if it actually happens. We found that for smaller impacts like the one that occurred at Chesapeake Bay, it didn't. This doesn't rule out larger impacts producing this effect."
"Grad student is lead author of article in Geology"
08 April 2008
Link: Western Michigan Article
----------
"Impact effects and regional tectonic insights: Backstripping the Chesapeake Bay impact structure"
Geology
Article: pp. 327–330
Volume 36, Issue 4 (April 2008)
Travis Hayden1,*, Michelle Kominz1, David S. Powars2, Lucy E. Edwards2, Kenneth G. Miller3, James V. Browning3, and Andrew A. Kulpecz3
1 Department of Geosciences, Western Michigan University, 1187 Rood Hall, 1903 W. Michigan Avenue, Kalamazoo, Michigan 49008, USA
2 United States Geological Survey, National Center, Reston, Virginia 20192, USA
3 Department of Geosciences, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854, USA
Abstract: The Chesapeake Bay impact structure is a ca. 35.4 Ma crater located on the eastern seaboard of North America. Deposition returned to normal shortly after impact, resulting in a unique record of both impact-related and subsequent passive margin sedimentation. We use backstripping to show that the impact strongly affected sedimentation for 7 m.y. through impact-derived crustalscale tectonics, dominated by the effects of sediment compaction and the introduction and subsequent removal of a negative thermal anomaly instead of the expected positive thermal anomaly. After this, the area was dominated by passive margin thermal subsidence overprinted by periods of regional-scale vertical tectonic events, on the order of tens of meters. Loading due to prograding sediment bodies may have generated these events.
Link: Geology Journal Reference
A Western Michigan University graduate student is the lead author of an article in the April issue of Geology magazine that explores how the crust of the Earth behaves after being hit by a comet or asteroid and could shed light on how the moon's surface was formed.
Travis Hayden, a graduate student in geosciences from Portage, Mich., is among seven authors who contributed to the article, titled "Impact effects and regional tectonic insights: Backstripping the Chesapeake Bay impact structure." Hayden's main advisor, Dr. Michelle Kominz, a WMU professor of geosciences, also contributed to the article.
Published by the Geological Society of America, Geology is one of the most popular and widely read earth science journals in print, with 20 or more thought-provoking articles each month. The article written by Hayden, Kominz and five other scientists examined the impact of an object, probably a comet or asteroid, that struck the Earth in the Chesapeake Bay area. The object was 1 to 1.5 miles in diameter and hit the Earth about 35 million years ago, Hayden says.
It was widely thought that such an impact would have long-lasting effects on the Earth's crust. In addition to forming a very large crater, scientists believed a significant amount of heat would have been generated in such a strike, melting a portion of the Earth's crust.
"The interesting thing was that we found it behaved exactly the opposite of what everybody expected," Hayden says. "Everyone had assumed that the impact released a whole bunch of heat, melted a lot of rocks and this heat actually changed how the crust behaves over time." Hayden says the impact did generate a lot of heat and melted a lot of rock, but most of the molten debris was thrown out of the crater. All the material that then filled in the crater afterward wasn't hot at all--it was cold.
And that affected what happened to the crust, Hayden says. Scientists had believed an impact and resulting melting of rock in the crater would have resulted in uplift within the crater followed by subsidence. Their results showed just the opposite happened. The crust subsided about 100 meters, and that was followed by uplift. "This was out of left field," Hayden says.
The results help to better understand how such impacts affect the crusts of the Earth and other bodies, including the moon, Hayden says.
"The seas of the moon, such as the Sea of Tranquility, are thought to be formed by this kind of melt, when a big impact came in, melted a whole lot of rock and then kind of paved everything out pretty smoothly" Hayden says. "But no one had been able to test it. So this was the first time we've ever been able to look at it in the real world to see if it actually happens. We found that for smaller impacts like the one that occurred at Chesapeake Bay, it didn't. This doesn't rule out larger impacts producing this effect."
"Grad student is lead author of article in Geology"
08 April 2008
Link: Western Michigan Article
----------
"Impact effects and regional tectonic insights: Backstripping the Chesapeake Bay impact structure"
Geology
Article: pp. 327–330
Volume 36, Issue 4 (April 2008)
Travis Hayden1,*, Michelle Kominz1, David S. Powars2, Lucy E. Edwards2, Kenneth G. Miller3, James V. Browning3, and Andrew A. Kulpecz3
1 Department of Geosciences, Western Michigan University, 1187 Rood Hall, 1903 W. Michigan Avenue, Kalamazoo, Michigan 49008, USA
2 United States Geological Survey, National Center, Reston, Virginia 20192, USA
3 Department of Geosciences, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854, USA
Abstract: The Chesapeake Bay impact structure is a ca. 35.4 Ma crater located on the eastern seaboard of North America. Deposition returned to normal shortly after impact, resulting in a unique record of both impact-related and subsequent passive margin sedimentation. We use backstripping to show that the impact strongly affected sedimentation for 7 m.y. through impact-derived crustalscale tectonics, dominated by the effects of sediment compaction and the introduction and subsequent removal of a negative thermal anomaly instead of the expected positive thermal anomaly. After this, the area was dominated by passive margin thermal subsidence overprinted by periods of regional-scale vertical tectonic events, on the order of tens of meters. Loading due to prograding sediment bodies may have generated these events.
Link: Geology Journal Reference
12 April 2008
K-T Asteroid is Smaller than Previous Estimates? (2.5 - 3.7 miles versus 9.3 - 12 miles in diameter)
University of Hawaii at Manoa geology and geophysics associate professor Greg Ravizza, left, and doctoral student Francois Paquay developed a method to use osmium isotope records from ocean sediments to determine the impact sizes of meteorites (Source: Star Bulletin).
Summary of the article appears below (as well as link to Science article)...
A University of Hawaii doctoral student has found that the huge asteroid crash believed to have wiped out the dinosaurs 65 million years ago was only about half the size of previous estimates.
Francois Paquay developed a method using osmium isotopes in deep-ocean sediments to determine sizes of meteorites that have collided with the Earth.
The asteroid believed to have created the Chicxulub Crater buried under Mexico's Yucatan Peninsula and caused the dinosaurs' extinction had been estimated to be 9.3 to 12 miles in diameter from crater simulations.
But by Paquay's calculations, the asteroid was about 2.5 to 3.7 miles in diameter.
Paquay's research with his adviser Gregory Ravizza was reported in yesterday's issue of the journal Science.
"UH student downsizes cataclysmic asteroid: Deep-sea sediments yield insight into the end of the dinosaurs"
Helen Altonn
12 April 2008
Star Bulletin
Link: Star Bulletin Article
Link: Space.com article
Link: NewScientist Article
Link: National Geographic Article
-----------
Science 11 April 2008:
Vol. 320. no. 5873, pp. 214 - 218
Reports
Determining Chondritic Impactor Size from the Marine Osmium Isotope Record
François S. Paquay,1* Gregory E. Ravizza,1 Tarun K. Dalai,1+ Bernhard Peucker-Ehrenbrink2
Decreases in the seawater 187Os/188Os ratio caused by the impact of a chondritic meteorite are indicative of projectile size, if the soluble fraction of osmium carried by the impacting body is known. Resulting diameter estimates of the Late Eocene and Cretaceous/Paleogene projectiles are within 50% of independent estimates derived from iridium data, assuming total vaporization and dissolution of osmium in seawater. The variations of 187Os/188Os and Os/Ir across the Late Eocene impact-event horizon support the main assumptions required to estimate the projectile diameter. Chondritic impacts as small as 2 kilometers in diameter should produce observable excursions in the marine osmium isotope record, suggesting that previously unrecognized impact events can be identified by this method.
1 Department of Geology and Geophysics, University of Hawaii, Honolulu, HI 96822–2225, USA.
2 Department of Marine Chemistry and Geochemistry, Woods Hole Oceano-graphic Institution, Woods Hole, MA 02543, USA.
+ Present address: Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur 721302, India.
Link: Science Magazine Article
Google Tech Talk from 2007: "The Use of Nuclear Explosives To Disrupt or Divert Asteroids"
Google Tech Talks
March 23, 2007
"The Use of Nuclear Explosives To Disrupt or Divert Asteroids"
Link: YouTube Video
07 April 2008
U.S. Department of Defense Funding of Asteroid Detection
Article on DoD involvement on asteroid detection...selections from the article...
Kirkland AFB, NM recently gave the University of Hawaii of Honolulu, Hawaii a modified contract for $8 million for the Panoramic Survey Telescope and Rapid Response System (PanSTARRS) multi-year program. The initial effort to develop and deploy a telescope data management system was awarded via a Grant to the University of Hawaii (considered a Minority Institute) and “as the various phases progressed, the Air Force determined that a Cooperative Agreement would be the more appropriate instrument as now we would be substantially involved.” At this time all $8 million has been committed (FA9451-06-2-0338, P00002).
PanSTARRS will address numerous science applications ranging from the structure of the Solar System to the properties of the Universe of the largest scales. It will be able to detect and catalog large numbers of earth-orbit crossing asteroids, or near earth objects (NEO) that present a potential threat to mankind. That last component to the mission is especially intriguing, as there is a long history of partial efforts in this direction within the US and elsewhere. So, where does this award fit in?
In many ways, it appears to be a replacement of existing efforts that have faltered, including GEODSS and NEAT. Kirtland AFB replied to DID:
“GEODSS is not involved in NEO (Near-Earth Object) work. Although “Planetary Defense” was an AF mission at one point, or at least showed up in Mission Needs statements, that was removed some time ago. At one point NEAT was located on one of the GEODSS telescopes on Maui. Because it interfered with the normal GEODSS mission, and because NEO disappeared from the AF mission, AFSPC paid AFRL to modify the 1.2-meter telescope to accommodate NEAT at prime focus. The NEAT camera was then moved to the 1.2 at AMOS.
Although the NEAT (Near-Earth Asteroid Tracking) program used the 1.2-meter telescope for a number of years, the NEAT camera was removed from the mount over a year ago and is being sent back to JPL. JPL and NASA were not paying customers for this program, the O&M was supplied by AFRL/RDSM using CA funding. When notified that AFRL funding was no longer available for support of NEAT, JPL responded that they did not have funding either. That’s when the NEAT program began to shut down. NEAT still has another camera at Palomar. At this point in time, GEODSS does not support the NEO mission, and the NEAT camera is no longer used on Maui.
"$8M for Astronomy & Asteroid Assessment"
06 April 2008
Link: Article
Kirkland AFB, NM recently gave the University of Hawaii of Honolulu, Hawaii a modified contract for $8 million for the Panoramic Survey Telescope and Rapid Response System (PanSTARRS) multi-year program. The initial effort to develop and deploy a telescope data management system was awarded via a Grant to the University of Hawaii (considered a Minority Institute) and “as the various phases progressed, the Air Force determined that a Cooperative Agreement would be the more appropriate instrument as now we would be substantially involved.” At this time all $8 million has been committed (FA9451-06-2-0338, P00002).
PanSTARRS will address numerous science applications ranging from the structure of the Solar System to the properties of the Universe of the largest scales. It will be able to detect and catalog large numbers of earth-orbit crossing asteroids, or near earth objects (NEO) that present a potential threat to mankind. That last component to the mission is especially intriguing, as there is a long history of partial efforts in this direction within the US and elsewhere. So, where does this award fit in?
In many ways, it appears to be a replacement of existing efforts that have faltered, including GEODSS and NEAT. Kirtland AFB replied to DID:
“GEODSS is not involved in NEO (Near-Earth Object) work. Although “Planetary Defense” was an AF mission at one point, or at least showed up in Mission Needs statements, that was removed some time ago. At one point NEAT was located on one of the GEODSS telescopes on Maui. Because it interfered with the normal GEODSS mission, and because NEO disappeared from the AF mission, AFSPC paid AFRL to modify the 1.2-meter telescope to accommodate NEAT at prime focus. The NEAT camera was then moved to the 1.2 at AMOS.
Although the NEAT (Near-Earth Asteroid Tracking) program used the 1.2-meter telescope for a number of years, the NEAT camera was removed from the mount over a year ago and is being sent back to JPL. JPL and NASA were not paying customers for this program, the O&M was supplied by AFRL/RDSM using CA funding. When notified that AFRL funding was no longer available for support of NEAT, JPL responded that they did not have funding either. That’s when the NEAT program began to shut down. NEAT still has another camera at Palomar. At this point in time, GEODSS does not support the NEO mission, and the NEAT camera is no longer used on Maui.
"$8M for Astronomy & Asteroid Assessment"
06 April 2008
Link: Article
04 April 2008
Update from Leonard David on U.S. NEO Action from Congress and NASA
Interesting update from Leonard David on actions in Congress and potentially by NASA on NEOs, full text of the post follows...
Keep an eye on a bill introduced in the House of Representatives by Congressman Dana Rohrabacher on Near Earth Objects (NEOs).
The NEO Preparedness Act calls upon the NASA Administrator to establish an Office of Potentially Hazardous Near-Earth Object Preparedness. That office would “prepare the United States for readiness to avoid and to mitigate collisions with potentially hazardous near-Earth objects in collaboration with other Agencies through the identification of situation- and decision-analysis factors and selection of procedures and systems.”
NASA has also been tasked to request the National Academy of Science to look into issues with detection of potentially hazardous NEOs and approaches to mitigate these hazards. The exact statement of task is still being hashed out, but that study should be underway in a couple of months or so, I’ve been advised.
According to Jim Green, Director of NASA’s Planetary Science Division, speaking at a recent meeting on outer planet exploration, part of the NEO assessment will focus on use of ground-based or space-based observations for NEOs and approaches to developing deflection capability.
It’s not within NASA’s charter to protect the planet from threatening NEOs, Green noted. Such a mission could go to the Department of Defense, he said, “but we’ll see how it goes.”
In NEO-related news, Green also reported on the huge Arecibo radio telescope in Puerto Rico. “We have confirmed with the NSF [National Science Foundation] that they will fully-fund Arecibo operations in fiscal year 2008,” he explained.
Conversation between NSF and NASA about funding Arecibo operations in upcoming years has begun, Green said.
"Near-Earth Object Protection: NASA or Defense Department Mission?"
Leonard David
LiveScience.com Blog
04 April 2008
Link: LiveScience.com Blog Post
Keep an eye on a bill introduced in the House of Representatives by Congressman Dana Rohrabacher on Near Earth Objects (NEOs).
The NEO Preparedness Act calls upon the NASA Administrator to establish an Office of Potentially Hazardous Near-Earth Object Preparedness. That office would “prepare the United States for readiness to avoid and to mitigate collisions with potentially hazardous near-Earth objects in collaboration with other Agencies through the identification of situation- and decision-analysis factors and selection of procedures and systems.”
NASA has also been tasked to request the National Academy of Science to look into issues with detection of potentially hazardous NEOs and approaches to mitigate these hazards. The exact statement of task is still being hashed out, but that study should be underway in a couple of months or so, I’ve been advised.
According to Jim Green, Director of NASA’s Planetary Science Division, speaking at a recent meeting on outer planet exploration, part of the NEO assessment will focus on use of ground-based or space-based observations for NEOs and approaches to developing deflection capability.
It’s not within NASA’s charter to protect the planet from threatening NEOs, Green noted. Such a mission could go to the Department of Defense, he said, “but we’ll see how it goes.”
In NEO-related news, Green also reported on the huge Arecibo radio telescope in Puerto Rico. “We have confirmed with the NSF [National Science Foundation] that they will fully-fund Arecibo operations in fiscal year 2008,” he explained.
Conversation between NSF and NASA about funding Arecibo operations in upcoming years has begun, Green said.
"Near-Earth Object Protection: NASA or Defense Department Mission?"
Leonard David
LiveScience.com Blog
04 April 2008
Link: LiveScience.com Blog Post
NEO News (04/04/08): Dave Morrison's Comments on Köfels Impact
Dave Morrison has a new NEO News out (04/04/08). Stories include the reporting of the March 23, 2008, New York Times reprintt of an Op-Ed from Arthur C. Clarke on NEOs and the impact Hazard, which he wrote in August 1994, shortly after the impact of Comet Shoemaker-Levy 9 on Jupiter. More interestingly he has a comment on the recent annoucement of a potential asteroid impact in Köfels, Austria that has been documented in a new book (see my post from 31 March 2008). Here are Dave's thoughts from the newsletter...
RECORD OF AN ANCIENT IMPACT?
Following are a press release from the University of Bristol and a news story from The Telegraph discussing a new claim that evidence has been found to connect a mysterious landslide in the Alps at Köfels, Austria, with the destruction of the ancient cities of Sodom and Gomorrah. Based on an interpretation an Assyrian copy of an earlier Sumerian clay tablet, the hypothesis is suggested that the tablet is an eyewitness account of a brilliant fireball that passed over Mesopotamia on 29 June 3123, travelling north-west. The authors further suggest that this object ended in an airburst over the Alps, triggering the 5-km-wide landslide at Köfels, Austria. Finally, much of the explosion energy formed a fireball that headed back toward western Asia, where it might have destroyed Sodom and Gomorrah, two cities mentioned in the Hebrew Bible that have not been identified by archeologists.
Obviously there are many poorly documented aspects of this hypothesis, perhaps related to its packaging for the press. I have not seen or read the book in which the ideas are presented. But questions begin with the interpretation by non-mid-east scholars of the clay tablet as showing a fireball, in which the size and shape as well as the trajectory of the incoming object was recorded. The Köfels landslide itself has not been dated, and most geologists do not think it is related to an impact. The idea of a fireball directed back to hit the ground again 3000 km away sounds pretty incredible, failing computer modeling to show this might have happened.
The bottom line for me is that this work has not been published in refereed scientific journals dealing with ancient mid-eastern history, or geology, or impact physics. Without such publication, it is difficult either to agree with or criticize this work.
David Morrison
RECORD OF AN ANCIENT IMPACT?
Following are a press release from the University of Bristol and a news story from The Telegraph discussing a new claim that evidence has been found to connect a mysterious landslide in the Alps at Köfels, Austria, with the destruction of the ancient cities of Sodom and Gomorrah. Based on an interpretation an Assyrian copy of an earlier Sumerian clay tablet, the hypothesis is suggested that the tablet is an eyewitness account of a brilliant fireball that passed over Mesopotamia on 29 June 3123, travelling north-west. The authors further suggest that this object ended in an airburst over the Alps, triggering the 5-km-wide landslide at Köfels, Austria. Finally, much of the explosion energy formed a fireball that headed back toward western Asia, where it might have destroyed Sodom and Gomorrah, two cities mentioned in the Hebrew Bible that have not been identified by archeologists.
Obviously there are many poorly documented aspects of this hypothesis, perhaps related to its packaging for the press. I have not seen or read the book in which the ideas are presented. But questions begin with the interpretation by non-mid-east scholars of the clay tablet as showing a fireball, in which the size and shape as well as the trajectory of the incoming object was recorded. The Köfels landslide itself has not been dated, and most geologists do not think it is related to an impact. The idea of a fireball directed back to hit the ground again 3000 km away sounds pretty incredible, failing computer modeling to show this might have happened.
The bottom line for me is that this work has not been published in refereed scientific journals dealing with ancient mid-eastern history, or geology, or impact physics. Without such publication, it is difficult either to agree with or criticize this work.
David Morrison
New Carusi Article in Icarus: ""Orbital and mission planning constraints for the deflection of NEOs impacting on Earth"
Andrea Carusi and his colleagues have a new article in Icarus on orbital issues associated with NEOs (specifically on 99942 Apophis and 2004 VD17). Following is an abstract and online commentary of the technical article. Note: This paper was available online in December 2007.
"Orbital and mission planning constraints for the deflection of NEOs impacting on Earth"
Icarus, Volume 194, Issue 2, April 2008, Pages 450-462
Andrea Carusi, Germano D'Abramo and Giovanni B. Valsecchi
Abstract: This paper is the third in a series. Paper 1 presented the results of numerical modeling of deflections of NEOs in route of collision with the Earth. The model was applied to a variety of dynamical cases including both asteroidal and cometary NEOs. Paper 2 introduced the concept of “distributed deflection,” i.e., the possibility to provide the ΔV necessary to deflect an object with a succession of maneuvers each of which would have been insufficient per se to obtain the desired result. In both papers no assumptions were made on the physical composition and structure of the NEO, nor on the details of the possible deflection maneuvers from the point of view of mission analysis. Moreover, ΔV-plots were computed assuming only along-track impulses (both in the positive and negative directions), because it is easy to demonstrate that in general this is energetically the most favorable configuration. Also in the present paper no assumptions were made on the physical composition and structure of the NEO, even if order of magnitude considerations are made on the physical feasibility of a deflection, in terms of the internal strength of the NEO. We present here the results of an investigation on the mission requirements necessary to deflect an object (or contribute to a succession of deflecting maneuvers) in terms of accessibility of the spacecraft terminal orbit from Earth with the current launchers.
Link: Icarus Article
---------
"How to Deflect an Asteroid"
Kunio Sayanagi
04 April 04, 2008
Ars Technica, LLC
By now, we have all heard about a handful of asteroids that are big enough to level a city or two and have a small but non-negligible chance of hitting Earth. Should we find one heading straight at Earth, what can we do about it, if anything at all?
That is the question addressed by Carusi and colleagues in a study published in the April issue of Icarus, a leading international journal in the planetary sciences. They conducted case studies of two near-Earth asteroids (NEAs) known as 99942 Apophis and 2004 VD17, whose initial orbit estimates indicated measurable probabilities of hitting Earth in 2036 and 2102, respectively. Although refinements to their orbital calculations through intensive follow-up observations have substantially lowered their chances of collisions with Earth, the authors treated the asteroids' initial orbital estimates as full-blown drills to study how such asteroids can be deflected, and to build realistic strategies to prepare ourselves for such events.
The report presents computer simulations that calculate the minimum orbital velocity change we must impart on the asteroids to deflect them away from Earth. A larger velocity change requires a stronger force, and thus imposes a greater technological and financial challenge. To make the exercise realistic, the authors considered performing their deflection maneuvers only when the asteroids cross the orbit of Earth—as the asteroids under consideration are NEAs, they have repeated Earth orbit crossings leading up to the predicted impact dates.
As expected, in general, the authors' calculations show that greater speed changes are needed as the hypothesized impact date comes closer. However, a careful examination also reveals that there are windows of opportunity in which deflection becomes considerably easier largely due to the relative orbital geometry of the asteroids and Earth. For example, in the case of 99942 Apophis, estimated to be a 400 meter chunk of rock, an impactor with 300 kg mass can deflect the asteroid to safety with a carefully angled interception on January 27th, 2020, about 16 years before impact. The authors note that such a deflection maneuver is already achievable with currently existing technologies. However, their study illustrates that things are not always that easy.
The other asteroid they considered, 2004 VD17, has an orbit closely overlapping that of Earth's over a longer span than 99942 Apophis does, and such orbital characteristics makes its deflection much more tricky. Still, the scientists found windows of opportunity such as one in 2021, 81 years before its hypothesized collision with Earth, in which an impactor weighing about a ton could deflect the asteroid away from Earth.
The authors' findings also come with a bit of bad news. While it may be technologically feasible to exert a force large enough to deflect 2004 VD17, their calculations also reveal that the impactor could shatter the asteroid, which is equivalent to converting an approaching rifle bullet into a shotgun round, with consequences that are unpredictable at best. 99942 Apophis, in contrast, should survive the relatively modest forces required to deflect it.
This study by Carusi et al. shows that deflecting real asteroids is within reach of currently existing technologies, given enough time and planning. By definition, NEAs orbit near Earth, so any that threaten us are expected to have a few close encounters with Earth, during which they are easy to find, before the final collision. Therefore, the long planning period considered in this study is realistic.
The current study's strategy will not, however, work well for deflecting objects with highly elliptical orbits such as long period comets; nevertheless, most objects that impose significant threats to Earth are NEAs since their orbits bring them so close to here. The study highlights the importance of efforts such as the SpaceWatch project hosted by the University of Arizona—its goal is to find and track all objects with chances of impacting Earth. It may well turn out that spotting an asteroid heading our way before it is too late is far more difficult than developing technologies to deflect them.
Link: Article
"Orbital and mission planning constraints for the deflection of NEOs impacting on Earth"
Icarus, Volume 194, Issue 2, April 2008, Pages 450-462
Andrea Carusi, Germano D'Abramo and Giovanni B. Valsecchi
Abstract: This paper is the third in a series. Paper 1 presented the results of numerical modeling of deflections of NEOs in route of collision with the Earth. The model was applied to a variety of dynamical cases including both asteroidal and cometary NEOs. Paper 2 introduced the concept of “distributed deflection,” i.e., the possibility to provide the ΔV necessary to deflect an object with a succession of maneuvers each of which would have been insufficient per se to obtain the desired result. In both papers no assumptions were made on the physical composition and structure of the NEO, nor on the details of the possible deflection maneuvers from the point of view of mission analysis. Moreover, ΔV-plots were computed assuming only along-track impulses (both in the positive and negative directions), because it is easy to demonstrate that in general this is energetically the most favorable configuration. Also in the present paper no assumptions were made on the physical composition and structure of the NEO, even if order of magnitude considerations are made on the physical feasibility of a deflection, in terms of the internal strength of the NEO. We present here the results of an investigation on the mission requirements necessary to deflect an object (or contribute to a succession of deflecting maneuvers) in terms of accessibility of the spacecraft terminal orbit from Earth with the current launchers.
Link: Icarus Article
---------
"How to Deflect an Asteroid"
Kunio Sayanagi
04 April 04, 2008
Ars Technica, LLC
By now, we have all heard about a handful of asteroids that are big enough to level a city or two and have a small but non-negligible chance of hitting Earth. Should we find one heading straight at Earth, what can we do about it, if anything at all?
That is the question addressed by Carusi and colleagues in a study published in the April issue of Icarus, a leading international journal in the planetary sciences. They conducted case studies of two near-Earth asteroids (NEAs) known as 99942 Apophis and 2004 VD17, whose initial orbit estimates indicated measurable probabilities of hitting Earth in 2036 and 2102, respectively. Although refinements to their orbital calculations through intensive follow-up observations have substantially lowered their chances of collisions with Earth, the authors treated the asteroids' initial orbital estimates as full-blown drills to study how such asteroids can be deflected, and to build realistic strategies to prepare ourselves for such events.
The report presents computer simulations that calculate the minimum orbital velocity change we must impart on the asteroids to deflect them away from Earth. A larger velocity change requires a stronger force, and thus imposes a greater technological and financial challenge. To make the exercise realistic, the authors considered performing their deflection maneuvers only when the asteroids cross the orbit of Earth—as the asteroids under consideration are NEAs, they have repeated Earth orbit crossings leading up to the predicted impact dates.
As expected, in general, the authors' calculations show that greater speed changes are needed as the hypothesized impact date comes closer. However, a careful examination also reveals that there are windows of opportunity in which deflection becomes considerably easier largely due to the relative orbital geometry of the asteroids and Earth. For example, in the case of 99942 Apophis, estimated to be a 400 meter chunk of rock, an impactor with 300 kg mass can deflect the asteroid to safety with a carefully angled interception on January 27th, 2020, about 16 years before impact. The authors note that such a deflection maneuver is already achievable with currently existing technologies. However, their study illustrates that things are not always that easy.
The other asteroid they considered, 2004 VD17, has an orbit closely overlapping that of Earth's over a longer span than 99942 Apophis does, and such orbital characteristics makes its deflection much more tricky. Still, the scientists found windows of opportunity such as one in 2021, 81 years before its hypothesized collision with Earth, in which an impactor weighing about a ton could deflect the asteroid away from Earth.
The authors' findings also come with a bit of bad news. While it may be technologically feasible to exert a force large enough to deflect 2004 VD17, their calculations also reveal that the impactor could shatter the asteroid, which is equivalent to converting an approaching rifle bullet into a shotgun round, with consequences that are unpredictable at best. 99942 Apophis, in contrast, should survive the relatively modest forces required to deflect it.
This study by Carusi et al. shows that deflecting real asteroids is within reach of currently existing technologies, given enough time and planning. By definition, NEAs orbit near Earth, so any that threaten us are expected to have a few close encounters with Earth, during which they are easy to find, before the final collision. Therefore, the long planning period considered in this study is realistic.
The current study's strategy will not, however, work well for deflecting objects with highly elliptical orbits such as long period comets; nevertheless, most objects that impose significant threats to Earth are NEAs since their orbits bring them so close to here. The study highlights the importance of efforts such as the SpaceWatch project hosted by the University of Arizona—its goal is to find and track all objects with chances of impacting Earth. It may well turn out that spotting an asteroid heading our way before it is too late is far more difficult than developing technologies to deflect them.
Link: Article
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