NASA probe makes new discoveries on asteroid Bennu

Asteroid Bennu

OSIRIS-REx spacecraft, via Wikimedia Commons

NASA's OSIRIS-REx spacecraft is orbiting the asteroid Bennu in preparation for its sample collection run.

Now it's clear that what actually speckles Bennu's surface is a shocking series of hefty boulders, some of which could be as large as 150 feet across.

In the study, published in the Nature Astronomy journal, the team identified infrared properties similar to those in a type of meteorite called carbonaceous chondrites. While a few other active asteroids are known, they represent only a few dozen out of the thousands of observed asteroids in the solar system - and have never been seen from such a prized vantage point. If you were standing inside the boundaries of Bennu's Roche lobe and slipped on a banana peel, for example, not much would happen-you'd be captured by the lobe and fall back to the surface. The OSIRIS-REx team determined the particles do not pose a threat to the spacecraft or the mission.

The discovery of plumes is one of the biggest surprises of my scientific career.

'And the rugged terrain went against all of our predictions. Bennu is already surprising us, and our exciting journey there is just getting started. In fact, it is doing so well, its navigation team knows down to a meter where OSIRIS-REx is heading. The asteroid is full of valuable materials that may even contain clues about how life began.

"It is not trivial to deliver a spacecraft with meter scale resolution to the surface of an asteroid in the microgravity environment", said Lauretta, who nevertheless said he was "confident" that the team would rise to the challenge.

The asteroid Bennu was thought to have wide, open areas suitable for the task.

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Scientists also discovered that the asteroid's spin is speeding up to the tune of around one second per century. While in the main asteroid belt between Mars and Jupiter, these objects would be constantly bombarded by impactors, but once they leave the main belt and become NEAs, they are subject to further evolutionary processes. Data from Earth-based observations had led the team to expect a smooth surface with a few large boulders. Instead, it's rough and crowded with boulders. Separately, two of the spacecraft's instruments, the MapCam color imager and the OSIRIS-REx Thermal Emission Spectrometer (OTES), have made detections of magnetite on Bennu's surface, which bolsters earlier findings indicating the interaction of rock with liquid water on Bennu's parent body.

Asteroids are easy to imagine as inert rocks flying through space.

"The first three months of OSIRIS-REx's up-close investigation of Bennu have reminded us what discovery is all about-surprises, quick thinking, and flexibility", said Lori Glaze, acting director of the Planetary Science Division at NASA Headquarters in Washington.

One concept into account by OSIRIS-REx's science crew is that the plume outbursts may very well be associated with Bennu's place in its orbit across the solar. OSIRIS-REx has been orbiting the asteroid since December 31 and Bennu is the smallest body to ever be orbited by a spacecraft.

The spacecraft launched on September 8, 2016 at 19:05 EST aboard an Atlas V rocket.

NASA is planning to land a probe called the OSIRIS-REx on the asteroid Bennu, which was more than 120 million kilometers from Earth as of December. It is due to collect a rock sample using its extendable arm but the sampling is proving more hard than anticipated due to the amount of larger boulders on the surface. And as the asteroid's whirling builds up speed, its Roche lobe might also be shrinking, along with the forces that are holding it together. Bennu completes a full revolution about once every four hours.

But over millions of years, that could cause the asteroid to lose pieces or blow apart.

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