NASA OSIRIS-REx probe detects ingredients for water on asteroid Bennu

The spacecraft found traces of hydrogen and oxygen molecules, known as hydroxyls, embedded in the rocky surface of the asteroid

NASA's OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer) spacecraft has detected signs of water on asteroid Bennu. The probe flew within 19 kilometres of the asteroid on 3rd December and discovered traces of hydrogen and oxygen molecules, known as hydroxyls, embedded in the rocky surface of the asteroid.

The observations were made by two spectrometres on board OSIRIS-Rex: Thermal Emissions Spectrometre and the Visible and Infrared Spectrometre.

"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 Ellen Howell, senior scientist at the University of Arizona's (UA) Lunar and Planetary Laboratory and a member of 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."

Bennu is a 500-metre-wide asteroid located about 2.25 million kilometres from Earth. This carbon-rich object orbits the Sun at about the same distance as the Earth. Bennu is thought to have formed by the leftovers from the formation of the solar system. Scientists also believe that the asteroid has remained largely unchanged over the past 4.5 billion years and could provide significant information about the formation of the solar system.

OSIRIS-REx arrived at asteroid Bennu on 3rd December after completing a two-year-long journey through deep space. But, before arriving at its final destination, the spacecraft - from August through early December - used three of its scientific instruments to make first observations of the asteroid. The probe's onboard spectrometres were able to detect signs of hydrated minerals on the surface about a month before the probe actually arrived at the asteroid.

Amy Simon, a scientist at NASA Goddard Space Flight Centre, says the discovery of hydrated minerals at Bennu confirms that Bennu is a leftover from the formation of the solar system and a perfect specimen for investigation of composition of primitive volatiles and organics in the solar system.

Scientists believe hydroxyl molecules are present across the asteroid in water-bearing clay minerals, suggesting an interaction between the rocky material and water at some point. It also suggests that Bennu's parent body - which would have been a much larger asteroid - must have hosted liquid water at some time.

In January 2019, OSIRIS-REx probe will fly within 1.4 and 1.9 kilometres of the asteroid. For next one year, it will orbit Bennu to collect more information about the surface and composition of the asteroid. In mid-2020, the probe will be directed to slowly descend and bounce off Bennu's surface to collect a sample of asteroid's top soil, which will be brought back to Earth in 2023.