On a rock two million kilometres away, water

Bennu, up close and personal.

Just days after successfully reaching its target, the asteroid known as Bennu. NASA’s OSIRIS-REx mission has discovered water – or, at least, a watery compound.

OSIRIS-REx, which stands for Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer, reached Bennu on December 3 after a journey of 2.2 million kilometres. 

Eventually, the probe will gather a small quantity of the asteroid’s surface dust, or regolith, and return it to Earth for analysis.

Bennu, up close and personal.
NASA/Goddard/University of Arizona

For the moment, however, it is tasked with making a series of in situ observations. 

The first of these concern gathering data by means of two onboard spectrometers, the OSIRIS-REx Visible and Infrared Spectrometer (OVIRS) and the OSIRIS-REx Thermal Emission Spectrometer (OTES).

Information from these sources received by NASA reveal the presence of hydroxyls – molecules of bonded oxygen and hydrogen – in clay minerals in the regolith. Bennu is too small to have ever contained liquid water, but researchers think that the hydroxyls – assumed to be present across the surface – are evidence that the asteroid’s parent body, by inference a much larger asteroid, may well have carried a watery cargo.

“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,” says Amy Simon, from NASA’s Goddard Space Flight Centre in Maryland, US. 

“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.”

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