Newswise — University of Colorado Boulder scientists have a front row seat to observe a NASA spacecraft as it approaches the asteroid Bennu, coming to within 4.5 miles of the space rock.

This meet up, which happened this morning, is the first in a series of planned close encounters between the Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer (OSIRIS-REx) and Bennu. A flyby taking place Dec. 4 will also be good practice for 2020, when the spacecraft will deploy its retractable arm to grab material from the asteroid’s surface and return it to Earth—the first time that a NASA mission will obtain such a sample.

And over the next several days, a team led by Distinguished Professor Daniel Scheeres will take the first stab at calculating a simple, but critical, number: Bennu’s mass.

Knowing the mass of this 1,600-foot-wide asteroid may provide new clues to how it moves and spins, what it’s made of and how likely it is to collide with Earth in the future.

“Right now, there’s a lot of uncertainty,” said Scheeres of the Ann and H.J. Smead Department of Aerospace Engineering Sciences. “Soon, those uncertainties are going to collapse down to show us what this body is like.”

He and his colleagues are also just excited to see Bennu up close for the first time from the operations center at the University of Arizona. “It’s going to be a great party—a lot of work, but a great party,” Scheeres said.

The University of Arizona leads science operations for OSIRIS-REx, which was built by the Colorado-based Lockheed Martin Space. NASA’s Goddard Space Flight Center in Maryland manages the overall mission.

The mission to visit Bennu provides scientists with a rare window to look back at the beginnings of Earth’s solar system, said Jay McMahon, an assistant professor in aerospace engineering at CU Boulder.

“One of the big draws for asteroids is that they’re leftovers from the formation of the solar system,” said McMahon, a co-investigator on the mission. “Bennu is a building block of the planets that didn’t end up in a planet.”

He and his colleagues will start work soon: McMahon explained that as OSIRIS-REx brushes past Bennu this time, the asteroid will exert a minute gravitational pull on the spacecraft. By precisely measuring that pull, his team can begin to map out the asteroid’s gravitational field, essential information for any spaceflight operation.

The group’s data will also put Bennu on the scale, giving scientists an estimate of its mass. Once the team knows how heavy Bennu is, OSIRIS-REx researcher Andrew French said, they can begin to guess at what it’s made of on the inside—past the reach of OSIRIS-REx’s arm.

“We’re going to go and touch Bennu and get a sample, but that’s only going to give us a look at the first couple of millimeters, or maybe centimeters, of the material on top,” French said. “So you don’t get a lot of insight to what it’s made of underneath.”

The researchers’ sneak peek at Bennu could provide scientists with a wealth of information about how the asteroid formed and how its orbit might evolve over time. Researchers believe that it’s possible, but extremely unlikely, that the asteroid could crash into our planet sometime between 2175-2199.