Title: Long-term impact risk for (101955) 1999 RQ36 Authors: Andrea Milani, Steven R. Chesley, Maria Eugenia Sansaturio, Fabrizio Bernardi, Giovanni B. Valsecchi, Oscar Arratia (Version v2)

The potentially hazardous asteroid (101955) 1999 RQ36 has the possibility of collision 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 10E-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 modelling of the nongravitational acceleration may be unnecessary.

Andrea Milani and his team of professional asteroid hunters have upgraded the probability that Asteroid 1999 RQ36 could hit the Earth between the years 2169 and 2199. The asteroid, also called (101955) 1999 RQ_{36}, is classified as an Apollo asteroid, with a diameter estimated to be about 580 meters and an approximated mass of 1.4 x 10^{11} kilograms.

An asteroid that had initially been deemed harmless has turned out to have a slim chance of hitting Earth in 160 years. While that might seem a distant threat, there's far less time available to deflect it off course.

Orbital elements: 1999 RQ36 PHA 0.001 Epoch 1999 Aug. 30.0 TT = JDT 2451420.5 Williams M 294.21519 (2000.0) P Q n 0.81560124 Peri. 64.72024 +0.39163818 -0.92011025 a 1.1345339 Node 2.23535 +0.80207228 +0.33921545 e 0.2071861 Incl. 6.00746 +0.45088756 +0.19578052 P 1.21 H 20.4 G 0.15 From 59 observations 1999 Sept. 11-14.

Title: Long term impact risk for (101955) 1999 RQ36 Authors: Andrea Milani, Steven R. Chesley, Maria Eugenia Sansaturio, Fabrizio Bernardi, Giovanni B. Valsecchi, Oscar Arratia

The potentially hazardous asteroid (101955) 1999 RQ36 has the possibility of collision 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 10E-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 modelling of the nongravitational acceleration may be unnecessary.