NASA Knew About Water on Bennu for a Month but Only Told Us About It Now

"At first we thought, 'Oh no, we messed up something.'"

For two years, scientists have wondered what OSIRIS-REx, the spacecraft that arrived on December 3 at the near-earth asteroid Bennu, might find. On Monday, NASA broke news that all that waiting was worth it: Instruments on the spacecraft confirmed that there’s water on Bennu.

The funny thing is, NASA scientists have actually known about the water for a month — well before OSIRIS even got cozy with the asteroid..

Amy Simon, Ph.D., NASA’s deputy instrument scientist for the OSIRIS-REx visible and near-IR Spectrometer (OVIRS) — one of the instruments that alerted scientists to this new evidence — tells Inverse that the signals from Bennu suggesting evidence of water were so strong that the team thought they’d made a mistake. They chose to sit on the data, checking it carefully, before making their announcement.

Bennu, explains Simon, seems to be replete with hydroxyls (molecules containing hydrogen and oxygen atoms), which are signs that the clay near its surface interacted with water in the past. The team got their first hint about Bennu’s hidden hydroxyls on November 2 at 4:00 am UTC, when Simon’s spectrometer detected something strange: There was evidence of hydroxls on every side of the asteroid, not just in one place.

“At first we thought, ‘Oh no, we messed up something in the instrument, there’s something in there that’s not real,’” Simon tells Inverse. “It took a while to convince ourselves that it’s actually there. When the other spectrometer confirmed it that was the nail in the coffin, so to speak. It’s there, it’s everywhere.”

Simon has been checking her data since then, and alerted the team a NASA several weeks ago. Only on Monday did NASA officially announce the news, ahead of the American Geophysical Union’s Fall Meeting in Washington D.C.

bennu samples Osiris
Eventually, OSIRIS will land on Bennu and collect samples

Exciting as they are, the signals aren’t proof that liquid water pooled on Bennu. It’s far too small for that, Simon explains. Rather, they are evidence that Bennu’s parent body, the larger asteroid from which it broke off, may have contained liquid water in the past. This is very good news for two parts of OSIRIS’ core mission to return samples of Bennu back to Earth for analysis and to illuminate what conditions were like in the early stages of the solar system. Part of Bennu’s appeal is that is has been relatively undisturbed since that period.

“We are seeing the evidence of past liquid, which locks the OH into the mineral structure,” Simon explains, referring to the oxygen and hydrogen atoms in water. If this is the case, she adds, it’s fair to hypothesize that this reaction was happening in other places throughout the early solar system, indicating that there was liquid to be found there.

“The reason that’s important is because we always talk about if meteorites, asteroids, comets could have delivered material to the earth, and so if we find that material is pretty widespread throughout the early solar system then yeah, they probably did deliver it to the early planet” she continues.

Going forward, this finding also might be important for the next few phases of OSIRIS’ work at Bennu. Since the spacecraft arrived, it has been searching for a safe and scientifically interesting place to land to collect samples, which will be returned to Earth. Doing so is tricky because the most scientifically interesting place might not actually be the safest place to land an expensive piece of equipment.

But since Bennu seems to have many different regions in which OSIRIS can collect these coveted hydrated minerals, NASA might not have to sacrifice safety for science, or vice versa. It’s a good early indicator that OSIRIS may be able to deliver on its promises.