Doppler imagery of 1999 RQ36 by NASA's Goldstone Radar.
"The total impact probability of asteroid ‘(101955) 1999 RQ36′ can be estimated in 0.00092 - approximately one-in-a-thousand chance - but what is most surprising is that over half of this chance (0.00054) corresponds to 2182," explains María Eugenia Sansaturio, of Spain's Universidad de Valladolid (UVA) and co-author of the international NEO study.
Recently published in the journal Icarus, this impact probability was calculated using two mathematical models to assess potential threats to Earth in the 22nd Century. 1999 RQ36 was singled out at the biggest threat.
Of course, a lot can happen to an errant space rock in 172 years, hence the odds of one-in-a-thousand. Although gravitational influences on the asteroid's trajectory can be fairly accurately calculated, other mechanisms acting on the rock are not so easily modeled.* The message to come out of this study is that potentially hazardous asteroids are out there and we are getting better at identifying which known asteroids pose the greater risk. But at what point do we decide to take action? 172 years into the future is a long time, and humans aren't exactly well-known for preparing for future events over those kinds of time scales. But time is one thing we'll need if we are to protect future generations from a potentially catastrophic impact event.
"If this object had been discovered after 2080, the deflection would require a technology that is not currently available," said Sansaturio. "Therefore, this example suggests that impact monitoring, which up to date does not cover more than 80 or 100 years, may need to encompass more than one century."
"Thus, the efforts to deviate this type of objects could be conducted with moderate resources, from a technological and financial point of view."
*For example, the "Yarkovsky effect" can modify an asteroid's orbit over long periods of time. As one side of a rotating body (i.e. an asteroid) is heated by the sun's radiation, the surface rotating away from the sun will be warmer than the surface rotating into sunlight. The hemisphere of the asteroid facing away from the sun will radiate the stored solar heat into space, so infrared photons will be emitted. Although very tiny, each photon carries a small amount of momentum away from the asteroid, giving it a tiny kick. In this case, the orbit of the rotating asteroid will very slowly spiral in toward the sun. Over 172 years, this effect could be significant.
Image: Comparative sizes of asteroids and comets visited by spacecraft. Compiled by Emily Lakdawalla (Planetary Society) & Ted Stryk. Credits: ESA, NASA, JAXA, RAS, JHUAPL, UMD, OSIRIS.