NASA’s probe OSIRIS-REx has reached asteroid 101955 Bennu after two long years, and has started to reveal the intriguing characteristics of this small world. One of the most interesting findings is the presence of oxygen and hydrogen bonded together in materials on the surface, strong evidence that the asteroid formed in the presence of water.

The researchers suspect that the oxygen-hydrogen molecules (known as hydroxyls) may exist all over Bennu, found in clay minerals, which would only have formed in the presence of water. Bennu is too small to have ever hosted liquid water, so the clay minerals must have originated from elsewhere. Possibly a much larger asteroid.

"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," Ellen Howell, senior research scientist at the UA's Lunar and Planetary Laboratory, or LPL, and a member of the mission's spectral analysis group, said in a statement.

"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."

The OSIRIS-REx mission is not exclusively to study Bennu from a distance. The spacecraft is going to collect a sample from the asteroid and bring it back to Earth in 2023. This first set of data will help inform the researchers of the structures on the surface of the asteroid. The team will have to study Bennu in detail to find the best place for the spacecraft to fly down and collect a sample. It will not actually be landing, it will just approach the surface where it will extend a robotic arm and collect the material. 

All these analyses will help planetary scientists understand better the formative years of the Solar System, and luckily it's all going well so far.

“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 spacecraft is currently surveying Bennu from a distance of 7 kilometers (4.4 miles) from which will move closer on December 31, as OSIRIS-REx enters its orbital phase. At that point, the spacecraft will be setting the record for the smallest object ever orbited and for the closest orbit ever by a spacecraft at less than 2 kilometers (1.24 miles).