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NASA's OSIRIS-REx spacecraft has found water on Watch Project Power Onlinethe asteroid Bennu, after finishing its two-year trip to the formation.

Sitting 12 miles (19 kilometres) from the surface, the probe has discovered water hidden inside the asteroid's clay minerals, thanks to data obtained from the probe's spectrometers.

During its two-year, 1.4 million-mile (2.2 million-kilometre) trip to the asteroid, instruments aboard OSIRIS-REx — that's the Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer — began to make scientific observations of Bennu between mid-August and early December.

Two of these instruments identified molecules on the asteroid, containing bonded oxygen and hydrogen atoms — these bad boys are known as hydroxyls.

These hydroxyls, NASA said, can be found across the asteroid in water-bearing clay minerals, which means Bennu's rocky surface once had contact with water.

But don't think Bennu was once brimming with lakes, or even puddles. According to NASA, the asteroid is actually too small to have ever hosted water in liquid form, but its parent body could have.

"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," Amy Simon, OVIRS deputy instrument scientist at NASA’s Goddard Space Flight Center, said in a statement.

OSIRIS-REx is NASA's first asteroid sample return mission. When the spacecraft lands on the surface of Bennu in July 2020, it will gather 4.4 pounds (2 kilograms) of rock over a year and a half to send back to Earth in a capsule.

"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," added Simon.

Additional reporting by Mark Kaufman.