The NASA spacecraft detected signs of hydrated minerals on Bennu's surface, suggesting that the asteroid's larger parent body once hosted liquid water.
NASA’s Osiris-REX spacecraft just arrived at asteroid Bennu on December 3rd. And the probe is already unearthing exciting details about its new home. Hydrated minerals on Bennu’s surface indicate that rocks on the asteroid once interacted with water.
“It’s one of the things we were hoping to find,” said Amy Simon (NASA Goddard Space Flight Center) in a December 10th press conference at a meeting of the American Geophysical Union in Washington, DC. “This is evidence of liquid water in Bennu’s past. This is really big news.”
As Osiris-REX approached Bennu, the spacecraft scanned the asteroid from afar. Two of its instruments measure how much the surface emits and reflects different wavelengths of light, a diagnostic tool for determining what atoms and molecules are present.
Those spectrometers picked up the presence of hydroxyls, molecules that contain oxygen and hydrogen atoms bonded together. The mission team suspects that these molecules are locked up in clay minerals, which means that at some point in Bennu’s past, water soaked its rocks.
Bennu itself is too small to have ever hosted liquid water. However, researchers suspect that the roughly 500-meter-wide (0.3-mile) space rock is actually a chunk of a much larger asteroid, knocked off long ago. The finding suggests that liquid water existed at some point on Bennu’s home world.
“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 Simon in a press release.
Osiris-REX is now keeping pace with the asteroid, sidling up closer every day before officially going into orbit around Bennu on December 31st. It will then spend the next couple of years investigating the surface, surveying for the perfect spot from which to grab a sample of material. The spacecraft will then return the sample to Earth, with a planned homecoming in 2023.