Very Early Warning: 1-in-1,000 Chance of Asteroid Impact in 2182

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Analysis by Ian O’Neill Tue Jul 27, 2010 02:33 PM ET 1 Comments | Leave a Comment
This isn’t an urgent call to arms, but it’s certainly a future date to consider. In the year 2182 — 172 years time — there’s the possibility that we might be hit by an asteroid with potential to cause some significant global turmoil. This long-distance forecast could help mankind determine whether asteroid deflection techniques are warranted, especially when given nearly two centuries of lead time.
SLIDE SHOW: Top 10 Ways to Stop an Asteroid

The not-so-romantically named (101955) 1999 RQ36 — discovered in 1999 — measures approximately 510 meters in diameter and is classified as an Apollo asteroid. Apollo asteroids pose a threat to our planet as they routinely cross Earth’s orbit.
With a one-in-a-thousand chance of 1999 RQ36 hitting Earth — with half of this probability indicating a 2182 impact — the threat might not sound too acute.
But compare this with the panic that ensued with the discovery of 99942 Apophis in 2004. Initially, it was thought there was a 1-in-233 chance of Apophis hitting us in 2029. This estimate was alarming; it was the first time an asteroid had been promoted to “Level 4” on the Torino Scale — a near-Earth object (NEO) impact hazard categorization method.
After further observations, the threat of an Apophis impact was lowered, and now the chance of the 270 meter space rock hitting us in 2029 is zero. The probability of impact during the next fly-by, in 2036, has recently been downgraded to a 1-in-250,000, and a third pass in 2068 has a tiny one-in-three million chance.
SLIDE SHOW: The top 10 near-Earth objects (NEOs) as selected by the Discovery News team.
Despite these shrinking odds, Apophis remains “the” doomsday asteroid in the public mindset — a situation that certainly wasn’t helped by the initial 1-in-233 odds and subsequent media frenzy.
Now we have 1999 RQ36, a bigger “potentially hazardous” asteroid, with a higher one-in-a-thousand chance of striking Earth in 2182.
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.
ANALYSIS: Will An Asteroid Hit Earth?
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.

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