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Complete NEO close encounter information: probabilistic approach

Presentation #405.09 in the session Asteroids: Planetary Defense (Poster)

Published onOct 23, 2023
Complete NEO close encounter information: probabilistic approach

For a large set of asteroids, the precise orbits are unknown. The area of possible positions of an asteroid (uncertainty region) can be not small and even reach the whole revolution around the Sun, while being extremely thin and stretched mostly along the nominal orbit of an asteroid. Because of that the close approach data of asteroids is not complete. The nominal position of the asteroid can be far from the Earth but at the same time the asteroid can have a close approach or even collide with the Earth. This is the reason why different centers for asteroid dynamics study (Minor Planet Center, Jet Propulsion Laboratory NASA, Institut de mécanique céleste et calcul des éphémérides…) publish different results for asteroids close approach data. They have different nominal solutions that lead to difference in outcome.

Here in this work, we are using Partial Banana Mapping method to compute possible close approach information of an asteroid with the Earth (time and minimal distance) including the probability of a close approach. We assume that the errors of equinoctial orbital elements have Gaussian distribution during the whole period of consideration (this century). This assumption is quite reasonable and allows us to take into account the fact that uncertainty region looks like a thin curvilinear ellipsoid stretched mostly along the nominal asteroid’s orbit. We propagate the orbit of the asteroid till when the Earth comes close to the uncertainty region. Then we find the point on the main line of curvilinear uncertainty ellipsoid which is closest to the Earth. We construct the uncertainty region around this point in 3D space and map it onto the target plane. With that we can compute the minimal possible distance of the close approach, the time when it can happen and the probability of such an event.

The method is tested on the case of asteroid 2005 QK76. We found 38 possible close approaches of this asteroid with the Earth, which have the probability of the approach higher than 1%, during 2005 until 2105. Our nominal solution found only 3 close encounters with the Earth, and the first one is during the discovery. The last encounter of the nominal solution (2093-02-27) has the probability of 1.9%, which is lower than many of the other ones. For 2 of the possible encounters the minimal possible distances are lower than the radius of the Earth (2030-02-26 and 2091-02-23) indicating the chances of hitting the Earth.

The proposed method provides complete information about close approaches of asteroids with the Earth, and can also explain the discrepancy in the results of different Near-Earth objects’ centers.

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