NASA’s Asteroid Sampling Mission Just Found Water On Bennu

OSIRIS-REx also produced a new 3D model of Bennu's shape and the highest resolution image of the near-Earth asteroid taken so far.

Artist's impression of NASA's OSIRIS-REx spacecraft swooping down on asterpid Bennu.
NASA's Goddard Space Flight Center

OSIRIS-REx also produced a new 3D model of Bennu's shape and the highest resolution image of the near-Earth asteroid taken so far.

One week after OSIRIS-REx caught up with the famous space rock that it had been chasing for 27 months, NASA has made a big announcement about its first asteroid-sampling mission.

Water On Asteroid Bennu

According to data picked up by two instruments on board NASA’s pioneering spacecraft, OSIRIS-REx has detected traces of water on the asteroid’ surface. More specifically, the probe uncovered that the 1,650-foot-wide space rock contains water-bearing clay minerals, which foster oxygen and hydrogen atoms that are bonded together in pairs called hydroxyls.

As NASA pointed out, the mission team suspects that these hydroxyl groups are widespread on the asteroid’s surface, which suggests that Bennu interacted with water sometime in its past.

As the Inquisitr previously reported, the near-Earth asteroid — located some 76 million miles away, between the orbits of Earth and Mars — is believed to have originated further out in the solar system. Scientists hypothesize that the carbon-rich asteroid broke off of a much bigger space rock nestled within the Asteroid Belt stretching between Mars and Jupiter and drifted closer to Earth.

Since Bennu has been deemed too small for liquid water to have ever existed on its surface, this new discovery suggests that the hydroxyls likely came from the asteroid’s parent body, which probably hosted liquid water at some point in its distant past.

Similar To Carbon-Rich, Water-Rich Meteorites

This revelation comes from data gathered by the probe’s two spectrometers, the OSIRIS-REx Visible and Infrared Spectrometer (OVIRS) and the OSIRIS-REx Thermal Emission Spectrometer (OTES). The two instruments took a good look at Bennu during the spacecraft’s asteroid approach phase — or the last stretch of 1.4 million miles covered by OSIRIS-REx before it finally parked within 12 miles of the space rock’s surface on December 3.

The OVIRS and OTES observations also revealed that Bennu gives off the same kind of light wavelength spectrum as carbonaceous chondrite meteorites — ancient meteorites that formed in the early days of the solar system and mashed together to create primitive asteroids. The great news is that this type of meteorites, which have often fallen on Earth, are known to contain both water and organic compounds — a boon for the OSIRIS-REx mission.

“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 Amy Simon, OVIRS deputy instrument scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “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.”

Clearest Image Of Bennu

While OVIRS and OTES were busy scanning the asteroid to uncover more clues about its composition, another instrument on board the OSIRIS-REx spacecraft was preoccupied with Bennu’s look.

The OSIRIS-REx PolyCam took advantage of the close proximity to this mysterious space rock and snapped 12 close-up photos from a distance of about 15 miles away. The snapshots, taken on December 2 — one day before the probe’s highly anticipated rendezvous with Bennu — were used to create a mosaic image which provides the clearest view yet of the diamond-shaped asteroid.

This mosaic image of asteroid Bennu is composed of 12 PolyCam images collected on Dec. 2 by the OSIRIS-REx spacecraft from a range of 15 miles.
This mosaic image of asteroid Bennu is composed of 12 PolyCam images collected on Dec. 2 by the OSIRIS-REx spacecraft from a range of 15 miles. NASA/Goddard/University of Arizona

According to the mission’s team, this is “the highest resolution imagery of asteroid Bennu so far.”

“Each pixel represents about 13 inches (33 cm) on Bennu’s surface,” the OSIRIS-REx team explained via Twitter.

Looking For A Landing Spot

This close-up view of asteroid Bennu enabled the scientists to take a better look at some of the space rock’s surface features. The new photos unveiled that the asteroid’s surface is strewn with a lot more boulders than previously estimated.

In fact, according to NASA, “Bennu’s surface material is a mix of very rocky, boulder-filled regions and a few relatively smooth regions that lack boulders.”

The OSIRIS-REx mission controllers will continue to monitor the asteroid’s rugged terrain in order to find the perfect spot for a touch-and-go landing, so that the spacecraft can eventually swoop down and gather samples from the carbon-rich, water-rich space rock.

3D Shape Model Of Asteroid Bennu

The entire OSIRIS-REx mission was planned based on a shape model of the unfamiliar space rock, developed in 2013 with the help of ground-based telescopes. This close proximity to Bennu has finally created the opportunity for the spacecraft to image the asteroid with the PolyCam and the OSIRIS-REx Camera Suite (OCAMS) to verify those initial projections.

The fresh, on-site observations have yielded a 3D shape model of asteroid Bennu, which confirms the scientists’ original predictions about the space rock’s diameter, rotation rate, inclination, and overall shape.

The only notable difference between the old model and the new one has to do with the estimated size of a large boulder spotted near Bennu’s south pole. The initial model indicated that the boulder was at least 33 feet tall. However, these latest measurements found it to be 164 feet high and 180 feet wide.

“Our initial data show that the team picked the right asteroid as the target of the OSIRIS-REx mission. We have not discovered any insurmountable issues at Bennu so far,” said Dante Lauretta, OSIRIS-REx principal investigator at the University of Arizona, Tucson. “The spacecraft is healthy and the science instruments are working better than required. It is time now for our adventure to begin.”

Going Into Orbit

The OSIRIS-REx spacecraft will continue its planned flyby’s of Bennu’s poles and equator until December 31, when the probe makes its first dive into the asteroid’s orbit. By that time, mission controllers will have gained enough data on the asteroid’s mass and gravitational pull to plan the spacecraft’s insertion into orbit.

Once this first orbital phase kicks in, OSIRIS-REx will circle the asteroid at a range between 0.9 miles and 1.24 miles (2.0 km) from its center, thereby “setting new records for the smallest body ever orbited by a spacecraft and the closest orbit of a planetary body by any spacecraft.”

OSIRIS-REx will orbit Bennu until mid-February 2019, then move on to another series of scheduled flybys marking the next survey phase of the asteroid. The spacecraft is slated to grab the asteroid samples in July 2020 and head back home on March 2021.