Evidence of water, particle plumes discovered on asteroid Bennu

Theresa Obrien
March 23, 2019

The asteroid was a lot more rugged than they expected, pushing the flight and sample-collection plans further down the timeline due to bumpy terrain.

But when OSIRIS-REx arrived at Bennu in December, the mission team quickly realized that their vision of a smooth, beachy asteroid was a little off.

NASA is hoping its spacecraft will return a sample to Earth in 2023.

"The discovery of plumes is one of the biggest surprises of my scientific career", said Dante Lauretta, OSIRIS-REx principal investigator at the University of Arizona, Tucson. "Bennu is already surprising us, and our exciting journey there is just getting started".

But there is optimism the new discoveries will not disrupt the mission to bring particles from Bennu back to earth. The researchers don't now understand why this is happening, but it poses no risk to the spacecraft. Then, in a very short time, the team increased the frequency of observations and subsequently detected additional particle plumes during the following two months. Not only is Bennu shooting particles out into the void, but the asteroid is also much more rugged than scientists originally thought - which may make it a little bit harder for the spacecraft to grab a sample. NASA said the mission's science team is continuing to study the particle plumes and their possible causes.

"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.

Studying Asteroid Bennu is helping NASA scientists to understand the solar system's origins, gather data on future asteroid mining and monitor the threat asteroids pose to Earth. "OSIRIS-REx's sample will help us answer some of the biggest questions about where we come from".

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Asteroid Bennu, a leftover fragment from the violent formation of the solar system, is an extraterrestrial time capsule for space scientists.

The OSIRIS-REx team also didn't anticipate the number and size of boulders on Bennu's surface. Additionally, OSIRIS-REx already discovered that water is lurking inside Bennu in hydrated clays, but the spacecraft also found that a mineral called magnetite is present. This means the planned Touch-and-Go (TAG) portion of the mission will need to be adjusted.

Some of these particles fall back to Bennu's surface, some fly away into space, and some enter orbit around Bennu, like a fleet of tiny satellites.

Lauretta believes that the team simply made the wrong inferences on Bennu's boulders based on the data they had, but that they were correct in some aspects of their interpretation. Rich Burns, OSIRIS-REx project manager at NASA's Goddard Space Flight Center and Coralie Adam, OSIRIS-REx flight navigator with KinetX, Inc. expressed confidence that the navigation and operations teams will be able to more accurately target the descent and achieve a "Bullseye TAG" in the summer of 2020.

A spacecraft's close-up observation of the near-Earth asteroid Bennu showed particle plumes erupting from its more rugged surface, which may alter the spacecraft's flight and sample collection plans in the coming year, US scientists said at a teleconference on Monday.

It has more than 200 boulders larger than 10 meters in diameter, and some stretching up to 30 meters, according to researchers writing in Nature Astronomy. The two closer images, obtained by the high-resolution PolyCam camera, show details of areas in the MapCam image, specifically a 50-foot (15 meter) boulder (top) and the regolith pond (bottom).

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