This area will cover relevant news of the threat to the planet from Near Earth Objects (NEOs) including concepts and designs for mitigation. All opinions are those of the author.

22 September 2009

Misc. Current Papers: Pan-STARRS 1 Detection Efficiency, (101955) 1999 RQ36 Impact Probability=10^-3, Yarkovsky on Eros/Itokawa, 2007 WD5 and Mars

New papers on asteroids published in the literature recently.

Detection of Earth-impacting asteroids with the next generation all-sky surveys
Volume 203, Issue 2, October 2009, Pages 472-485

Peter Vereš a, Robert Jedicke b, Richard Wainscoat b, Mikael Granvik b, Steve Chesley c, Shinsuke Abe d, Larry Denneau b and Tommy Grav e

a-Faculty of Mathematics, Physics and Informatics, Comenius University, Mlynska Dolina, 842 48 Bratislava, Slovakia
b-University of Hawai’i, Institute for Astronomy, 2680 Woodlawn Drive, Honolulu, HI 96822-1897, USA
c-Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
d-Institute of Astronomy, National Central University, No. 300, Jhongda Rd, Jhongli City, Taoyuan County 320, Taiwan
e-Department of Physics and Astronomy, Bloomberg 243, Johns Hopkins University, 3400 N. Charles St., Baltimore, MD 21218-2686, USA


We have performed a simulation of a next generation sky survey’s (Pan-STARRS 1) efficiency for detecting Earth-impacting asteroids. The steady-state sky-plane distribution of the impactors long before impact is concentrated towards small solar elongations (Chesley, S.R., Spahr T.B., 2004. In: Belton, M.J.S., Morgan, T.H., Samarashinha, N.H., Yeomans, D.K. (Eds.), Mitigation of Hazardous Comets and Asteroids. Cambridge University Press, Cambridge, pp. 22–37) but we find that there is interesting and potentially exploitable behavior in the sky-plane distribution in the months leading up to impact. The next generation surveys will find most of the dangerous impactors (>140 m diameter) during their decade-long survey missions though there is the potential to miss difficult objects with long synodic periods appearing in the direction of the Sun, as well as objects with long orbital periods that spend much of their time far from the Sun and Earth. A space-based platform that can observe close to the Sun may be needed to identify many of the potential impactors that spend much of their time interior to the Earth’s orbit. The next generation surveys have a good chance of imaging a bolide like 2008 TC3 before it enters the atmosphere but the difficulty will lie in obtaining enough images in advance of impact to allow an accurate pre-impact orbit to be computed.

Link: Icarus Article (Detection of Earth-impacting asteroids with the next generation all-sky surveys)

Long term impact risk for (101955) 1999 RQ36
Volume 203, Issue 2, October 2009, Pages 460-471

Andrea Milani a, Steven R. Chesley b, Maria Eugenia Sansaturio c, Fabrizio Bernardi a, d, Giovanni B. Valsecchi d and Oscar Arratia c

a-Department of Mathematics, University of Pisa, Largo Pontecorvo 5, 56127 Pisa, Italy
b-Jet Propulsion Laboratory, Calif. Inst. of Tech., Pasadena, CA 91109, USA
c-E.T.S. de Ingenieros Industriales, University of Valladolid, Paseo del Cauce 59, 47011 Valladolid, Spain
d-IASF-Roma, INAF, via Fosso del Cavaliere 100, 00133 Roma, Italy


The potentially hazardous Asteroid (101955) 1999 RQ36 has a possibility of colliding with the Earth in the latter half of the 22nd century, well beyond the traditional 100-year time horizon for routine impact monitoring. The probabilities accumulate to a total impact probability of approximately 10-3, with a pair of closely related routes to impact in 2182 comprising more than half of the total. The analysis of impact possibilities so far in the future is strongly dependent on the action of the Yarkovsky effect, which raises new challenges in the careful assessment of longer term impact hazards.

Even for asteroids with very precisely determined orbits, a future close approach to Earth can scatter the possible trajectories to the point that the problem becomes like that of a newly discovered asteroid with a weakly determined orbit. If the scattering takes place late enough so that the target plane uncertainty is dominated by Yarkovsky accelerations then the thermal properties of the asteroid, which are typically unknown, play a major role in the impact assessment. In contrast, if the strong planetary interaction takes place sooner, while the Yarkovsky dispersion is still relatively small compared to that derived from the measurements, then precise modeling of the nongravitational acceleration may be unnecessary.

Link: Icarus Article (Long term impact risk for (101955) 1999 RQ36)

The Yarkovsky effect is not responsible for small crater depletion on Eros and Itokawa
Volume 203, Issue 1, September 2009, Pages 112-118

David P. O’Brien a

a-Planetary Science Institute, 1700 E. Ft. Lowell, Suite 106, Tucson, AZ 85719, USA


The near-Earth Asteroids Eros and Itokawa show a pronounced lack of small (less, approximate100 m) craters, the vast majority of which were formed during their time in the main belt, and this has been cited as possible evidence that small (less, approximate10 m) impactors are efficiently removed from the main belt by the Yarkovsky effect. Using well-tested models for the evolution of the main-belt size distribution and the evolution of crater populations on asteroid surfaces, I show that a pronounced lack of small impactors would require size-dependent removal far stronger than can result from the Yarkovsky effect (or any other known process). Furthermore, such strong removal would lead to wavelike perturbations in the main-belt and near-Earth asteroid size distributions that are inconsistent with their observed size distributions, as well as the cratering records on asteroid surfaces. A more likely explanation is that processes on asteroid surfaces, such as seismic shaking, are responsible for erasing small craters after they form.

Link: Icarus Article (The Yarkovsky effect is not responsible for small crater depletion on Eros and Itokawa)

Impact solutions of Asteroid 2007 WD5 with Mars
Volume 203, Issue 1, September 2009, Pages 119-123

I. Włodarczyka a

a-Chorzów Astronomical Observatory, Al. Planetarium 4, WPKiW, 41-500 Chorzów, Poland


A method for computing impact probabilities between asteroids and the planet Mars is presented that uses impact clones and validation analysis based on a normal distribution of computed errors. This method uses OrbFit software, and we present a calculation of the impact probabilities between Asteroid 2007 WD5 and Mars, which passed within about 20,000 km of the martian surface on January 30, 2008. This method can be generalized for computing impact probabilities between asteroids and other planets including Earth. Presented method applies in principal the same technique already in use for years at the JPL NASA and by the group of researchers at the University of Pisa [Milani, A., Chesley, S.R., Sansaturio, M.E., Tommei, G., Valsecchi, G.B., 2005a. Icarus 173, 362].

Link: Icarus Article (Impact solutions of Asteroid 2007 WD5 with Mars)

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