Christmas Day for scientists who study asteroids is coming in just two months when a small spacecraft carrying material from a distant rubble pile will land in a Utah desert.

The return of the OSIRIS-REx sample container on September 24 will cap the primary mission to capture material from an asteroid—in this case, the carbonaceous near-Earth asteroid Bennu—and return some of its pebbles and dust to Earth.

It has been a long time coming. This mission launched seven years ago and has been in the planning and development phase for over a decade. To say the scientists who have fought for and executed this mission are anxious and excited is an understatement. But there is an additional frisson with OSIRIS-REx, as scientists are not entirely sure what they've been able to pull away from the asteroid.

Touch-and-go

Bennu is essentially a pile of rubble, and to gather this material, the spacecraft employed a unique "touch-and-go" maneuver. Immediately after the end of a robotic arm touched down on Bennu, the spacecraft fired a canister of pure nitrogen gas, causing a cloud of material to rise from the surface of Bennu. The sampling arm lingered on the surface for seconds to suck up this material before backing away.

The catch is that scientists aren't quite sure what they've got or how much of it they've retrieved. Scientists are confident that they've collected at least 60 grams of material from Bennu, or about the mass of a Snickers candy bar. More likely, they've collected at least a few hundred grams, if not more. But they won't know until the spacecraft lands and the capsule is opened up.

"It adds to the tension for us, for sure," said Nicole Lunning, a planetary scientist at NASA's Johnson Space Center in Houston.

The samples will be met by a flotilla of scientists and helicopters at the Utah Test and Training Range when it lands on the morning of the 24th. There, the dusty heat shield will be removed. The sample carrier will then be flown to Houston's Ellington Field on the next day, where it will be put into a clean room. Almost immediately, scientists will remove asteroid dust from the exterior of the sample container and begin a preliminary analysis.

Clean rooms

On Monday, Lunning led a tour of the facility where, over the course of about 10 days, scientists and technicians at Johnson Space Center will meticulously open the sample container and begin to place its contents into a special, pizza-sized tray with eight compartments. This work will be supervised by Lunning, the primary curator of the OSIRIS-REx samples in Houston.

It will be done inside a brightly lit ISO-5 clean room on the second floor of Building 31 at the space center, with epoxy floors and white walls. Here, the samples will be carefully characterized, and a catalog will be made of all the small rocks and dust particles.

OSIRIS-REx has a team of about 200 scientists dedicated to the mission, and they will have six months to conduct their initial analyses of the material gleaned from the surface of the asteroid. After this time, the samples will be available to outside scientists for additional research.

Origin of life

Scientists are taking great care with samples from the asteroid Bennu because they do not want to contaminate them with organic material from Earth. It is hoped that, by understanding the material that makes up Bennu, scientists will be able to obtain a snapshot of conditions as far back as the origin of the Solar System, when such asteroids were formed. By characterizing the organic material and the minerals surrounding it, scientists may be able to tease out some details about how life originated in the Solar System.

For the last half-century, beginning with the first rocks brought back from the Moon by the Apollo mission, NASA has been storing its prized materials from the Solar System inside carefully maintained vaults and clean rooms at the Houston facility. As part of its Astromaterials Research and Exploration Science program, this facility houses meteorites that originated on Mars, bits of the Solar wind, comet particles, and 127,000 cataloged samples of Moon rocks.

"Every sample here has a story to tell," said Eileen Stansbery, who leads the program. "It is our job to preserve these samples for scientists to use for decades to come."