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INTRODUCTION

Impact Probabilities computed with Yarkovsky effect

There are few cases of asteroids with very good orbit detrmination for which even the minute push from non-gravitational perturbations is enough to change the impact risk. To handle these cases, we have developed the new, experimental software OrbFit version 4.3. It handles the Yarkovsky non-gravitational effect as a model uncertainty, that is solves for 7 parameters instead of 6. This applies both to the orbit determination (at the initial epoch) and to the propagations used in the impact monitoring procedure.

Currently there are two Near Earth Asteroids on our risk pages with this kind of more advanced impact probability computation. The first is (99942) Apophis, which formerly had several possible impactors, but now has a main impactor in 2068 with a probability which cannot be properly computed unless the Yarkovsky non-gravitational effect is taken into account.

The second case has been posted recently (30 April 2014) and is asteroid 2009 FD, which has been observed much less than Apophis. Thus it is not yet possible to determine the amount of Yarkovsky effect from the observational data, still the additional uncertainty due to its unknown value is relevant to make possible the main impactor in the year 2185.

There are two other cases on which the Yarkovsky effect is critical in making possible impacts, and on these the work is in progress: (101955) Bennu and (29075) 1950 DA. For Bennu we are giving the impact probabilities from a joint work done with JPL. For 1950 DA the impact possibility occurs in the year 2880: it is not yet listed on our risk pages because of technical difficulties in the computation.

We do not know if there are other possible impactors beyond the time limit of our current operational impact monitoring, which is now fixed at 100 years from the date of the computation. Progress in extending this time limit will need significant theoretical and computational advances.





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