NASA Says Dwarf Planet Ceres Likely Harbors Salty Mud

Фото: photojournal.jpl.nasa.gov

Computer-generated image of Ahuna Mons, with elevation exaggerated by a factor of two (1 September 2016).

Topographic and gravity-field observations made by NASA’s Dawn spacecraft - currently in orbit around the 940-diameter dwarf planet - now indicate that there are small amounts of salty liquid water (or brine) in Ceres’ interior.

Researchers already knew that Ceres likely has a long-frozen subsurface ocean. But this new analysis --- detailed in two new papers set to appear in the Journal of Geophysical Research and the journal Earth and Planetary Science Letters - marks the first tentative confirmation of significant liquid water in Ceres’ mantle .

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Yet most of Ceres' ancient ocean is now likely frozen and bound up in its crust, and has been that way for more than 4 billion years, NASA and the American Geophysical Union (AGU), note in a joint statement. This ancient ocean can now be found in the form of ice, frozen clathrate hydrates and salts, NASA and the AGU say. They point out that a clathrate hydrate is a cage of water molecules surrounding a gas molecule, some 100 to 1,000 times stronger than water ice.

Was the liquid ocean there long enough to spawn life?

“Very difficult to tell,” Julie Castillo-Rogez, NASA’s Dawn project scientist and one of the two studies’ co-author, told me. “We think that Ceres could have had habitable conditions early on; what we don’t know is when those conditions started freezing.”

It might be that present conditions are not very favorable to life, says Castillo-Rogez; we just don’t know.

Some 100 million years after Ceres’ formation, Castillo-Rogez says its ocean could have formed a global shell up to 100 kilometers thick. Yet the ocean had to be below a crust, because, with no atmosphere, water would not have been stable on Ceres’ surface. Thus, Castillo-Rogez says the early interior structure of Ceres was akin to icy moons (like Europa or Enceladus) with an ocean sandwiched between a core made up of rocky material and an ice-rich crust.

“But the ocean just froze over time,” said Castillo-Rogez. “It’s not been lost; it’s now there in the crust.”

NASA has extended the Dawn mission until late next year and hopes to maneuver the craft into an orbit that would take to within 200 kilometers of Ceres’ surface, or about twice as close as its previous lowest approach. But to come to any conclusions about whether life might have had time to develop on this intriguing dwarf planet, NASA will ultimately need a follow-on lander mission.

“We need to sample places where we think there’s the expression of the ocean at Ceres’ surface”, said Castillo-Rogez.

A prime spot to test this idea would be at Ahuna Mons - a 4 kilometer-tall mountain on Ceres where enough volcanic activity may have coughed up some small portion of Ceres’ ancient ocean.

Bruce Dorminey, Contributor