Asteroid 1999 RQ36 may or may not pose a future problem for our planet — the chances of an impact with the Earth in 2182 are now estimated at roughly one in 1800. But learning more about it will help us understand the population of near-Earth objects that much better, one of several reasons why the OSIRIS-REx mission is significant. The acronym stands for Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer, a genuine mouthful, but a name we’ll be hearing more of as the launch of this sample-return mission approaches in 2016.
The target asteroid, 575 meters in diameter, has been the subject of extensive study not only by ground-based telescopes including the Arecibo planetary radar but also by the Spitzer Space Telescope. We know that 1999 RQ36 orbits the Sun every 1.2 years and crosses the Earth’s orbit every September, with a shape and rotation rate that are well understood. OSIRIS-REx will carry pristine samples of carbonaceous materials of a quality never before analyzed in our laboratories back to Earth, using a sample collecting device that will inject nitrogen to stir up surface materials for capture and storage on the journey back.
This University of Arizona video gives an overview of the mission:
Dante Lauretta (University of Arizona) is deputy principal investigator for OSIRIS-REx:
“OSIRIS-REx will usher in a new era of planetary exploration. For the first time in space-exploration history, a mission will travel to, and return pristine samples of a carbonaceous asteroid with known geologic context. Such samples are critical to understanding the origin of the solar system, Earth, and life.”
The 60 gram sample will be collected in a surface contact that lasts for no more than five seconds. In fact, it’s hard to describe this as a landing. A little over a year ago I quoted Joseph Nuth (NASA GSFC) on the problems of sampling a quickly rotating object of this size. Think in terms of two spacecraft trying to link rather than one trying to land on a surface:
“Gravity on this asteroid is so weak, if you were on the surface, held your arm out straight and dropped a rock, it would take about half an hour for it to hit the ground,” says Nuth. “Pressure from the sun’s radiation and the solar wind on the spacecraft and the solar panels is about 20 percent of the gravitational attraction from RQ36. It will be more like docking than landing.”
The spacecraft will spend more than a year orbiting the asteroid before collecting the samples for return to Earth in 2023. You’ll recall the Japanese Hayabusa spacecraft’s mission to Itokawa, with the first return of asteroid materials in June of 2010. 1999 RQ36 may be a more interesting target given its carbonaceous composition. The idea is to go after an asteroid rich in organics, the kind of object that might have once seeded the Earth with life’s precursors.
OSIRIS-REx should also provide useful data on the Yarkovsky effect, which induces uneven forces on a small orbiting object because of surface heating from sunlight. You can imagine how tricky the Yarkovsky effect is to model given the variables of surface composition, but learning more about it will be helpful as we learn to tighten the precision of projected asteroid orbits. That, in turn, can help us decide whether or not a particular object really does pose a threat to the Earth at some future date.
Meanwhile, we’re keeping a close eye on the Dawn mission, now closing on Vesta and eventually destined to orbit Ceres. Both missions will add significantly to our knowledge of asteroids and their role in Solar System development, but Dawn will not return samples of either of its destinations to Earth. OSIRIS-REx also recalls the Stardust spacecraft, which returned particles from comet Wild 2 in 2006. And like Stardust, OSIRIS-REx will be capable of an extended mission if called upon — Stardust (renamed NExT, for New Exploration of Tempel 1) performed a flyby of previously visited comet Tempel 1 earlier this year.