New data from two instruments on NASA’s OSIRIS-REx spacecraft — the OSIRIS-REx Visible and Infrared Spectrometer (OVIRS) and the OSIRIS-REx Thermal Emissions Spectrometer (OTES) — reveal the presence of hydroxyls, molecules that contain oxygen and hydrogen atoms bonded together, on the surface of asteroid Bennu. According to the mission science team, these hydroxyl groups may exist globally across the asteroid in hydrated clay minerals, meaning that at some point, the rocky material interacted with water.
An artist concept of the OSIRIS-REx spacecraft. Image credit: NASA / Goddard.
“The presence of hydrated minerals across the asteroid confirms that Bennu, a remnant from early in the formation of the Solar System, is an excellent specimen for the OSIRIS-REx mission to study the composition of primitive volatiles and organics,” said OVIRS deputy instrument scientist Dr. Amy Simon, a researcher at NASA’s Goddard Space Flight Center.
“When samples of this material are returned by the mission to Earth in 2023, scientists will receive a treasure trove of new information about the history and evolution of our Solar System.”
“This finding may provide an important link between what we think happened in space with asteroids like Bennu and what we see in the meteorites that scientists study in the lab,” said Dr. Ellen Howell, a senior scientist in the Lunar and Planetary Laboratory at the University of Arizona and a member of the mission’s spectral analysis group.
“It is very exciting to see these hydrated minerals distributed across Bennu’s surface, because it suggests they are an intrinsic part of Bennu’s composition, not just sprinkled on its surface by an impactor.”
This mosaic image of asteroid Bennu is composed of 12 images collected on December 2, 2018 by OSIRIS-REx’s PolyCam instrument from a range of 15 miles (24 km). Image credit: NASA / NASA’s Goddard Space Flight Center / University of Arizona.
Additionally, data obtained from the OSIRIS-REx Camera Suite (OCAMS) corroborate ground-based radar observations of Bennu and confirm the original model developed in 2013 by the science team.
That model closely predicted the asteroid’s actual shape, with Bennu’s diameter, rotation rate, inclination, and overall shape presented almost exactly as projected.
“Radar observations don’t give us any information about colors or brightness of the object, so it is really interesting to see the asteroid up close through the eyes of OSIRIS-REx,” said OSIRIS-REx science team chief Dr. Michael Nolan, also from the Lunar and Planetary Laboratory at the University of Arizona.
“As we are getting more details, we are figuring out where the craters and boulders are, and we were very pleasantly surprised that virtually every little bump we saw in our radar image back then is actually really there.”
One outlier from the predicted shape model is the size of the large boulder near Bennu’s south pole.
The ground-based shape model calculated this boulder to be at least 33 feet (10 m) in height.
Preliminary calculations from OCAMS observations show that the boulder is closer to 164 feet (50 m) in height, with a width of approximately 180 feet (55 m).
Bennu’s surface material is a mix of very rocky, boulder-filled regions and a few relatively smooth regions that lack boulders. However, the quantity of boulders on the surface is higher than expected.
The scientists presented the results December 10 at the Annual Fall Meeting of the American Geophysical Union in Washington, D.C.
They will make further observations at closer ranges to more accurately assess where a sample can be taken on Bennu to later be returned to Earth.
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Victoria E. Hamilton et al. Spectral Analysis for the OSIRIS-REx Mission at Bennu. AGU 2018 Fall Meeting, abstract # P22A-01
