OSIRIS-Rex To Study Asteroid Yarkovsky Effect
February 8, 2013

NASA Prepping For OSIRIS-REx Asteroid Mission

Lee Rannals for redOrbit.com — Your Universe Online

NASA will be launching a new mission in 2016 to help estimate what kind of impact an asteroid would make if it struck Earth.

The OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security, and Regolith Explorer) mission will travel to a potentially hazardous asteroid (PHA), and make measurements of the Yarkovsky effect. This effect is a push on an asteroid that happens when it is warmed up by the sun and then later re-radiates this heat in a different direction as infrared radiation.

The Yarkovsky effect takes place because it takes time for things to heat up and cool down, similar to a brick building.

"A brick building can feel warm even in the early evening hours, because it is radiating away the heat accumulated from an entire day of sunshine," said Edward Beshore of the University of Arizona in Tucson, deputy principal investigator for NASA's OSIRIS-REx asteroid sample return mission.

An asteroid acts the same way, as it radiates most of its heat from its late "afternoon side," giving it the small Yarkovsky push.

Currently, NASA says there are more than 1,300 asteroids at least 150 yards across that have the potential of impacting Earth one day due to their orbital path.

"Anything over a few hundred yards across that appears to be on a collision course with Earth is very worrisome," says Bershore. "When an asteroid makes a close pass to Earth, the gravitational pull from our planet changes the asteroid's orbit."

He said how this change will affect the evolution of the asteroid's orbit is difficult to predict because there are other small forces acting on the asteroid to change its orbit.

"The most significant of these smaller forces is the Yarkovsky effect — a minute push on an asteroid that happens when it is warmed up by the sun and then later re-radiates this heat in a different direction as infrared radiation," Bershore added.

OSIRIS-REx will be making precise measurements of the Yarkovsky effect on a PHA known as "1999 RQ36."

According to Steve Chesley, an astronomer at NASA's Jet Propulsion Laboratory, this PHA has a probability of 1 in 2,400 chance of impacting Earth in the 22nd century. Taking radar measurements of RQ36 will give scientists good data on its range, and can help them understand the asteroid's behavior pertaining to the Yarkovsky effect.

"We estimate the position of the asteroid and what its orbit must be like by using Newtonian and Relativistic physics. If we see a deviation from the estimated position, then it must be due to the sum of all these other small forces, and the greatest of these we believe to be the Yarkovsky effect," Bershore said.

OSIRIS-REx will be arriving at RQ36 in 2018 and will remain in orbit around it until 2021. NASA believes this mission will help it double its estimate of the Yarkovsky force on RQ36.

After gathering data from the mission, scientists at the space agency will use what they learn about the Yarkovsky effect to help estimate the effects of other asteroids.

"What we want to be able to do is create a model that says okay if you give me an asteroid of this size, made of this composition, with this kind of topography, I can estimate for you what the Yarkovsky effect will be," says Beshore.

This isn't NASA's first attempt to grasp a better understanding of a large asteroid. The space agency's Dawn mission just left its first target, Vesta, back in September 2012.

This spacecraft first reached the giant asteroid on July 15, 2011 and helped map out the space rock to give scientists a better peak at its early formation. Now, Dawn is on its way to the dwarf planet Ceres, where it is expected to arrive in early 2015.