Science

NASA spacecraft finds signs of water on Bennu asteroid

astreoid

NASA’s OSIRIS-REx spacecraft has already detected evidence of water
on its target, the asteroid Bennu, just a week after arriving.

The OSIRIS-REx mission’s goals include understanding what kinds of stuff asteroids contain, characterizing Bennu’s motion in case its trajectory ever threatens Earth, and learning about what the Solar System was like in its earliest days. The mission even aims to grab a sample of Bennu and bring it back to Earth for further study. Today, NASA announced that OSIRIS-REx has already collected data related to the first and third of those goals by spotting signs of water.

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Sitting 12 miles (19 kilometres) from the surface, the probe has discovered water hidden inside the asteroid’s clay minerals, thanks to data obtained from the probe’s spectrometers.






During its two-year, 1.4 million-mile (2.2 million-kilometre) trip to the asteroid, instruments aboard OSIRIS-REx — that’s the Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer — began to make scientific observations of Bennu between mid-August and early December.

The discovery suggests that liquid water was once plentiful in the interior of Bennu’s parent body, which scientists think was a roughly 62-mile-wide (100 kilometers) rock in the main asteroid belt between Mars and Jupiter. (Bennu is likely a pile of rubble that coalesced after a massive impact shattered that larger object hundreds of millions of years ago.)

OSIRIS-REx’s main goal involves helping scientists better understand the solar system’s early days and the role that asteroids like Bennu may have played in delivering water and the chemical building blocks of life to Earth. So, the water find is big news for the mission team.

“We targeted Bennu precisely because we thought it had water-bearing minerals and, by analogy with the carbonaceous chondrite meteorites that we’ve been studying, organic material,” OSIRIS-REx principal investigator Dante Lauretta, of the University of Arizona, said today during a news conference at the annual fall meeting of the American Geophysical Union in Washington, D.C.






“That still remains to be seen — we have not detected the organics
— but it definitely looks like we’ve gone to the right place,” Lauretta
added.

The $800 million OSIRIS-REx mission (whose name is short for “Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer”) launched in September 2016 and began its Bennu-approach phase in mid-August of this year.

Measurements made over the past four months by the spacecraft’s two
onboard spectrometers revealed the presence of molecules containing
hydroxyls — bonded-together oxygen and hydrogen atoms — on Bennu,
Lauretta and fellow team members announced today. Mission scientists
think these hydroxyls are widespread across the asteroid, locked into
clay minerals.

Scientists also announced today that OSIRIS-REx’s observations pretty
much confirm Bennu shape models devised a half-decade ago by researchers
using radar data gathered by the Arecibo and Goldstone dishes here on
Earth. That’s good news, Lauretta said, because the mission team drew up
its plans based on those earlier shape models.

In addition, NASA today released OSIRIS-REx’s best look at Bennu to date. The dazzling photo, taken on Dec. 2 just before the spacecraft’s official asteroid arrival, shows Bennu in unprecedented detail and highlights the rugged nature of its surface. (Arrival is different than orbit, by the way; OSIRIS-REx won’t begin circling Bennu until Dec. 31.)






Bennu is littered with boulders, to an extent that Lauretta and his
colleagues deemed surprising. The biggest of these jutting rocks is
about 165 feet tall by 180 feet wide (50 by 55 m), mission team members
said.

The abundance of these obstacles means the OSIRIS-REx team must plan
out its sample-grabbing activities in great detail and with great care.
But that’s fine, team members said, because there’s still plenty of time
to choose and characterize a sampling site; OSIRIS-REx isn’t scheduled
to snag any Bennu bits until July 2020.

This material will come down to Earth in a special return capsule in
September 2023. Scientists around the world can then scrutinize the
sample with a variety of laboratory equipment, making observations that
address the main mission goals as well as a variety of other questions. 

For example, the mission could help researchers better understand the resource potential of Bennu-like asteroids — whether they contain enough accessible water to support in-space mining operations. And OSIRIS-REx’s measurements at Bennu will reveal key details about the forces that affect asteroids’ paths through space, which should help fine-tune predictions of the trajectories of potentially hazardous space rocks, NASA officials have said.

“We have an awesome asteroid to explore,” Lauretta said. “It’s a dream come true, and it’s an honor and a privilege to be able to lead a program like this for NASA and for the United States and, really, for the world.”










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