Asteroids are leftovers from the cloud of gas and dust – the solar nebula -- that collapsed to form our sun and the planets about 4.5 billion years ago. As such, they contain the original material from the solar nebula, which can tell us about the conditions of our solar system's birth.
In some asteroids, this material was altered by heat and chemical reactions, either because they collided with other asteroids, or because they grew so large that their interiors became molten.
An artist's concept of the OSIRIS-REx spacecraft taking a sample from asteroid RQ36
That's what makes RQ36 special. It's small and appears to have been altered very little, preserving the snapshot of our solar system's infancy. It's also rich in carbon, an element used in many of the organic molecules necessary for life. Organic molecules have been found in meteorite and comet samples, indicating that some of life's ingredients can be created in space. Scientists want to see if they are also present in RQ36.
"This asteroid is a time capsule from before the birth of our solar system," said Bill Cutlip, one of the leaders of Goddard's effort to propose a mission called OSIRIS-REx that will return a sample from RQ36.
The mission will be significantly more capable than the original OSIRIS proposal. "OSIRIS was a basic sample return mission," says Joseph Nuth a scientists on the OSIRIS-REx Project.
"OSIRIS-REx adds more instruments to give us a complete map of the surface composition and 3-D shape, or topography, of the asteroid. It will allow us to put our sample in the proper geologic context, so we'll have a much better idea of what we're really sampling," says Nuth.
Once the asteroid has been completely analyzed from orbit, the science team will pick the location to take a sample. OSIRIS-REx will be gradually brought closer to the site, and an arm
with a sampling mechanism at the end will be extended to touch the surface and collect the sample.
"Like the Moon rocks from the Apollo missions, samples of RQ36 will keep on giving. They'll be analyzed for decades after mission is complete, using new techniques we can't even imagine now, to test new theories of how we came to be," said Nuth.
Sample return, however, isn't the only objective for the mission. This asteroid crosses Earth orbit, and the International Astronomical Union's Minor Planet Center has officially classified RQ36 as a "potentially hazardous asteroid," with a slight chance – one in 1,800 – of an impact in the year 2170.
Piloting a spaceship near an asteroid is not easy. Most are lumpy and rotate more rapidly than planets, which makes for challenging landings. These small objects have feeble gravity, so other forces can significantly influence the spacecraft's position.
"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. 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," adds Nuth.
The mission will also help to better track the orbits of asteroids that might hit Earth by accurately measuring the "Yarkovsky effect" for the first time. The Yarkovsky effect is a small push on an asteroid that happens when the asteroid absorbs sunlight and emits heat. The small push adds up over time, and it is uneven due to an asteroid's various surface materials, wobble, and rotation.
There's no sure way to predict an Earth-approaching asteroid's orbit unless you can factor in how the Yarkovsky effect will change that orbit, according to the team. "It's like trying to make a complex, banking shot in a game of pool with someone shaking the table and kicking the legs," said Nuth.
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