National Geographic Daily News
The OSIRIS spacecraft.

The OSIRIS-Rex craft visits an asteroid in an artist's rendering.

Image courtesy NASA

Andrew Fazekas

for National Geographic News

Published August 6, 2010

There's a mountain-size asteroid on a potential collision course with Earth, and NASA has plans to pay it a visit.

The asteroid 1999 RQ36 made headlines last week with the announcement that the space rock could hit our planet in 2182. But a handful of scientists have had their eyes on this asteroid since 2007, planning a sample-return mission designed to help us better predict—and avoid—impact hazards.

The mission, called OSIRIS-Rex (Origins Spectral Interpretation Resource Identification Security Regolith Explorer), is one of two finalists in the current competition for funding under NASA's New Frontiers program, up against a proposed mission to land on Venus. The selected mission will be announced in summer 2011.

If OSIRIS-Rex gets the green light, the spacecraft will launch in 2016 with the goal of mapping and bringing back pieces of the asteroid.

(Related: "Hayabusa Spacecraft Returns With Fiery Show.")

The team wants to go to RQ36 specifically because it's thought to be rich in material that's remained unchanged since the early days of the solar system—and because the asteroid's orbit makes the space rock easy to reach.

"Being one of the easiest targets to get to coincidently means that it also can easily hit us, too," said Michael Drake, director of the Lunar and Planetary Laboratory at the University of Arizona, who would lead the OSIRIS-Rex team.

"When we were putting this mission proposal together, however, we really didn't connect those dots."

Asteroid Risk to Earth Still Highly Uncertain

Orbiting between 83 million and 126 million miles (133 million and 203 million kilometers) from the sun, RQ36 passes within about 280,000 miles (450,000 kilometers) of Earth's orbit. As a result, NASA has officially classified RQ36 as a "potentially hazardous asteroid."

The predictions that made waves last week suggest the 1,900-foot (580-meter) space rock has a one-in-a-thousand chance of hitting Earth in 2182.

While RQ36 would not create a global civilization-threatening impact, the asteroid would pack quite a punch, said Clark Chapman, a planetary scientist at Southwest Research Institute in Boulder, Colorado, who's not part of the OSIRIS-Rex or RQ36-assessment teams.

"It would be an enormous impact, like hundreds of the biggest nuclear bombs ever built exploding at once, creating a crater maybe 10 kilometers [6.2 miles] across."

But even with the new calculations, there's still way too much uncertainty about the asteroid's orbital path, said OSIRIS-Rex team leader Drake. To know if RQ36—or any space rock—really has our planet in its cross-hairs, we need a clearer understanding of what's called the Yarkovsky effect.

This effect occurs when an object absorbs sunlight. The resulting heat emanating from the object's surface gives it slight nudges. Over time, these tiny pushes can greatly affect an asteroid's orbital path.

(See "Asteroids Spin Faster Due to Solar Power, Studies Show.")

"While, for objects as big as Earth, such a small force is irrelevant, for those that are less than 20 kilometers [12.4 miles] in diameter, it becomes a significant enough force that it changes the orbit of the object," Drake said.

So far the Yarkovsky effect has been nearly impossible to measure from ground-based observations because of unknown variations in asteroids' surfaces and in their rotations and wobbles.

As a result, many of today's predictions of doomsday asteroids do not include this effect when calculating their orbits.

"This means that something that looks totally harmless right now may actually be the most probable thing to hit us," Drake said. "There is no doubt that it is a big effect and may in fact be the dominant effect throwing a wrench into the works."

Asteroid Visit to Keep Us From Being Fooled?

The proposed OSIRIS-Rex mission would reach RQ36 in 2019 and would start by mapping the asteroid in visible wavelengths through far-infrared wavelengths to figure out its basic chemical and mineralogical makeup.

The mission would also collect a sample of the asteroid's surface to return to Earth by 2023.

The hope is that OSIRIS-Rex can measure the Yarkovsky effect accurately for the first time and give us a better understanding of asteroid structure.

"Our mission would be able to tell us a lot about the nature of its surface and what its made of," Drake said. "There is no doubt that this information will be crucial to defending ourselves from an impact from this or any other asteroid."

Southwest Research Institute's Chapman added that, in addition to deciding whether RQ36 really poses a threat, we still need to figure out how we might nudge the space rock out of a potentially catastrophic trajectory.

"There are already indications from RQ36's shape that its surface is composed of loose materials," Chapman said. "That is good for retrieving a sample but poor for anchoring some device on the asteroid to move it."

(See "'Killer Asteroid' Debate Pits Gravity Tractors Against Bombs, Projectiles.")

In general, he added, "any close-up study of an asteroid will increase our appreciation of the physical nature of these diverse bodies and thus improve the likelihood that we won't be fooled when and if we try to interact with the body to move it."

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