OSIRIS-REx mission researchers have been able to measure the Yarkovsky effect on target asteroid 1999 RQ36 so precisely that they know how far it will drift in its orbit over the coming years.

The Yarkovsky effect occurs as thermal force from the sun radiates heat on objects. They absorb and reflect the radiation in return, and the resulting reaction acts as a tiny rocket thrust.

Decades ago, it was unclear to researchers how near-Earth objects were formed. Most scientists agreed that there had to be some sort of interaction with the sun or Jupiter, due to their massive gravitational fields, that sent new asteroids into the inner solar system.

“But you’d think that would have already been taken care of too because Jupiter’s been out there for billions of years,” said Ed Beshore, a deputy principal investigator of OSIRIS-REx. “So something must be pushing these asteroids probably from the asteroid belt, into what’s called a resonance zone. That means that every time they come by, Jupiter can tug on it, and actually throw this guy into the inner solar system.”

OSIRIX-REx Co-Investigator Steve Chesley of NASA’s Jet Propulsion Laboratory and Radar Astronomer Mike Nolan at Arecibo Observatory in Puerto Rico have performed a series of tests to measure the Yarkovsky effect. Their findings showed that the amount of force pushing on the 1999 RQ36 is about the weight of three grapes. This force, while extremely small, acts constantly on the object over the years and eventually alters the orbital pattern.

“This tells us a lot about how hazardous objects are created and how they might change their orbit over time because of this effect, and that’s important for us to predict the long term history of some of these objects and what’s going to happen to them,” Beshore added.

The Yarkovsky effect varies due to the target object’s thermal properties, such as the surface roughness, composition and size. Large objects, such as Earth, are safe from this kind of pushing, as it is a force that effects smaller matter.

“We can plan its orbit based on the elements we receive on the ground, but the Yarkovsky effect changes that. So it might change its predicted location over time,” said Daniel Wibben, a graduate student employee of the Science Processing and Operations Center. “What we want to try and use the Yarkovsky effect for is, ‘Will it ever affect it so that it comes into a collision course with Earth?’”

Researchers have in fact confirmed that asteroid 1999 RQ36 runs across the Earth’s orbital road.

“We do know that late in the 22nd century it does get pretty close to the Earth,” Beshore said, adding that the asteroid has a one in one-thousandth chance of colliding with the planet. This asteroid is about 560 meters across and about half a kilometer, or 1/3 of a mile in diameter. “If it were to hit Earth, it would cause a 7-kilometer crater,” said Veronica Bray via email, an associate staff scientist in impact cratering.

The effects on the target area would be disastrous. By comparison, if the team’s target asteroid were to impact Tucson, it would send out a thermal pulse over a 120-kilometer radius, which would be farther than Nogales, Bray said. The pulse would cause third-degree burns and clothing to spontaneously ignite, and a seven or eight level magnitude earthquake that would destroy a substantial amount of infrastructure. If this collision were to happen, however, it would not be large enough to kill a significant portion of the population or change the global climate. Most operations in testing against these collisions involve deflecting the asteroid by explosives, or tugging on it with a gravity tractor spacecraft, Bray said.

According to NASA’s current impact risk table, 1999 RQ36 is ranked as the second-most dangerous near-Earth object out of a hundred others. The first is 2011 AG5, discovered last year and its orbital patterns are still unclear.