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Banner image: Artist's conception听of the OSIRIS-REx spacecraft collecting a sample of loose, rocky material from the surface of the asteroid Bennu. (Credit: NASA's Goddard Space Flight Center)

CU Boulder scientists have a front row seat today to observe a NASA spacecraft as it arrives at the asteroid Bennu, coming to within 4.5 miles of the space rock.

This close approach, followed by a flyby Dec. 4, is the first in a series of planned meet ups between the (OSIRIS-REx) and Bennu. Today's encounter will听be good practice for 2020, when the spacecraft will deploy its retractable arm to grab material from the asteroid鈥檚 surface and return it to Earth鈥攖he first time that a NASA mission will obtain such a sample.

Scientists from CU Boulder are playing an important role in that historic snatch-and-run. 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鈥檚 mass.

Knowing the mass of this 1,600-foot-wide asteroid will reveal valuable information about not just Bennu, but other chunks of space debris, too, Scheeres said. That includes how they move and spin, what they鈥檙e made of and how scientists might knock them aside if they鈥檙e flying toward Earth.听

鈥淥nce we get the first flyby and we nail the first mass, that鈥檚 going to be hugely important,鈥� said Scheeres of the Ann and H.J. Smead Department of Aerospace Engineering Sciences. 鈥淏ecause right now, there鈥檚 a lot of uncertainty. Soon, those uncertainties are going to collapse down to show us what this body is like.鈥�

Solar system leftovers

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. 鈥淚t鈥檚 going to be a great party鈥攁 lot of work, but a great party,鈥� Scheeres said.听

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

Read a story about CU Boulder alumni who have worked on the OSIRIS-REx mission at Lockheed Martin Space.听

OSIRIS-REx launched in September 2016 and has traveled more than one billion miles since, looping around the Earth鈥檚 sun to rendezvous with Bennu. The asteroid has an orbit that brings it relatively close to Earth about once every six years.

This meeting will provide scientists with a rare window to look back at the beginnings of Earth鈥檚 solar system, said Jay McMahon, an assistant professor in aerospace engineering at CU Boulder.听

鈥淥ne of the big draws for asteroids is that they鈥檙e leftovers from the formation of the solar system,鈥� said McMahon, a co-investigator on the mission. 鈥淏ennu is a building block of the planets that didn鈥檛 end up in a planet.鈥�
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But to dive into that past, OSIRIS-REx will first need to get close enough to Bennu to snag a sample of the loose, rocky material from its surface in 2020. That鈥檚 where the CU Boulder team comes in. 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鈥檚 gravitational field, essential information for any spaceflight operation.听

鈥淥nce we have this data, we can plug it back in and that will help with planning out the trajectory for the rest of the mission,鈥� said Daniel Brack, a graduate student in aerospace engineering and a participant in the project.听

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Running the odds

The group鈥檚 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鈥檚 made of on the inside鈥攑ast the reach of OSIRIS-REx鈥檚 arm.听

鈥淲e鈥檙e going to go and touch Bennu and get a sample, but that鈥檚 only going to give us a look at the first couple of millimeters, or maybe centimeters, of the material on top,鈥� French said. 鈥淪o you don鈥檛 get a lot of insight to what it鈥檚 made of underneath.鈥�

The researchers鈥� 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鈥檚 possible, but extremely unlikely, that the asteroid could crash into our planet sometime between 2175-2199.

For now, this week鈥檚 flyby will mark the culmination of a lot of hard work for the CU Boulder researchers.听

鈥淎ll of a sudden, it鈥檚 here and it鈥檚 really exciting,鈥� McMahon said.