CU Boulder Scientists To Help Measure The Mass Of Asteroid Bennu

December 3, 2018 – This morning, NASA’s Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer (OSIRIS-REx) spacecraft closed in on asteroid Bennu and began proximity operations. OSIRIS-REx will spend the next year and a half scanning and mapping the asteroid in preparation for a pristine sample collection to be returned to Earth in 2023.

CU Boulder scientists are in a unique position to observe the spacecraft as it navigates around asteroid Bennu, coming to within 4.5 miles of the space rock. A team led by University of Colorado Distinguished Professor Daniel Scheeres is at the operations center at the University of Arizona where they 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.”

As OSIRIS-REx brushes past Bennu, the asteroid will exert a minute gravitational pull on the spacecraft. By precisely measuring that pull, the 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 Earth sometime between 2175 and 2199.

More importantly, the OSIRIS-REx mission will provide scientists with a rare opportunity to look back at the beginnings of Earth’s solar system, said Jay McMahon, an assistant professor in aerospace engineering at CU Boulder. A pristine sample from Bennu will help scientists investigate how planets formed and how life began, as well as improve our understanding of asteroids. Asteroids like Bennu contain natural resources, such as water, organics and metals. Future space exploration and economic development may rely on asteroids for these materials.

“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.”

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