NASA’s Newly Arrived OSIRIS-REx Spacecraft Already Discovers Water on Asteroid

Asteroid Bennu
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 (24 km).
Credits: NASA/Goddard/University of Arizona

Recently analyzed data from NASAs Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer (OSIRIS-REx) mission has revealed water locked inside the clays that make up its scientific target, the asteroid Bennu.

During the missions approach phase, between mid-August and early December, the spacecraft traveled 1.4 million miles (2.2 million km) on its journey from Earth to arrive at a location 12 miles (19 km) from Bennu on Dec. 3. During this time, the science team on Earth aimed three of the spacecrafts instruments towards Bennu and began making the missions first scientific observations of the asteroid. OSIRIS-REx is NASAs first asteroid sample return mission.

Data obtained from the spacecrafts two spectrometers, the OSIRIS-REx Visible and Infrared Spectrometer (OVIRS) and the OSIRIS-REx Thermal Emission Spectrometer (OTES), reveal the presence of molecules that contain oxygen and hydrogen atoms bonded together, known as hydroxyls. The team suspects that these hydroxyl groups exist globally across the asteroid in water-bearing clay minerals, meaning that at some point, Bennus rocky material interacted with water. While Bennu itself is too small to have ever hosted liquid water, the finding does indicate that liquid water was present at some time on Bennus parent body, a much larger asteroid.

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 NASAs 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.

Additionally, data obtained from the OSIRIS-REx Camera Suite (OCAMS) corroborate ground-based telescopic observations of Bennu and confirm the original model developed in 2013 by OSIRIS-REx Science Team Chief Michael Nolan and collaborators. That model closely predicted the asteroids actual shape, with Bennus diameter, rotation rate, inclination, and overall shape presented almost exactly as projected.

One outlier from the predicted shape model is the size of the large boulder near Bennus south pole. The ground-based shape model calculated this boulder to be at least 33 feet (10 meters) in height. Preliminary calculations from OCAMS observations show that the boulder is closer to 164 feet (50 meters) in height, with a width of approximately 180 feet (55 meters).

Bennus 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 team 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.

This preliminary shape model of asteroid Bennu was created from a compilation of images taken by OSIRIS-RExs PolyCam camera during the spacecrafts approach toward Bennu during the month of November. This 3D shape model shows features on Bennu as small as six meters.
Credits: NASA/Goddard/University of Arizona

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.

The mission currently is performing a preliminary survey of the asteroid, flying the spacecraft in passes over Bennus north pole, equator, and south pole at ranges as close as 4.4 miles (7 km) to better determine the asteroids mass. The missions scientists and engineers must know the mass of the asteroid in order to design the spacecrafts insertion into orbit because mass affects the asteroids gravitational pull on the spacecraft. Knowing Bennus mass will also help the science team understand the asteroids structure and composition.

This survey also provides the first opportunity for the OSIRIS-REx Laser Altimeter (OLA), an instrument contributed by the Canadian Space Agency, to make observations, now that the spacecraft is in proximity to Bennu.

The spacecrafts first orbital insertion is scheduled for Dec. 31, and OSIRIS-REx will remain in orbit until mid-February 2019, when it exits to initiate another series of flybys for the next survey phase. During the first orbital phase, the spacecraft will orbit the asteroid at a range of 0.9 miles (1.4 km) to 1.24 miles (2.0 km) from the center of Bennu setting new records for the smallest body ever orbited by a spacecraft and the closest orbit of a planetary body by any spacecraft.

Goddard provides overall mission management, systems engineering and the safety and mission assurance for OSIRIS-REx. Dante Lauretta of the University of Arizona, Tucson, is the principal investigator, and the University of Arizona also leads the science team and the missions science observation planning and data processing. Lockheed Martin Space Systems in Denver built the spacecraft and is providing flight operations. Goddard and KinetX Aerospace are responsible for navigating the OSIRIS-REx spacecraft. OSIRIS-REx is the third mission in NASAs New Frontiers Program. NASAs Marshall Space Flight Center in Huntsville, Alabama, manages the agencys New Frontiers Program for the Science Mission Directorate in Washington.

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