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In 2007, NASA launched a spacecraft called Dawn to study a dwarf planet called Ceres in the asteroid belt — where millions of rocky objects dance soundlessly like a cosmic ballet.
After analyzing the spacecraft's survey of the dwarf planet, scientists say Ceres once hosted a global ocean — now completely frozen over, according to a study recently published in the journal Nature.
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Nearby dwarf planet Ceres hosts vast underground ocean, say scientists
Seven new studies were published in the journal Nature analyze the extended mission data from Dawn at length, scrutinizing Ceres' ostensibly mundane, lifeless shell of a dwarf-planet existence and uncovering definitive proof that it's actually an ocean world.
"The new results confirm the presence of liquid inside Ceres," said a planetary scientist and co-author of six of the new studies Julie Castillo-Rogez of NASA's Jet Propulsion Laboratory (JPL). The new presence of wetness in the solar system means Ceres — the closest-known dwarf planet to Earth — may have once been habitable, raising the possibility that similar dwarf planets may still host life, reports CNET.
Ceres' frozen-over ocean isn't completely frozen
Ceres is roughly 2.5 times smaller than Pluto, and Dawn zipped across its unmanageably dark skies during its prime 2015 mission. While there, it photographed a series of mysterious bright spots at the center of the Occator crater — a 60-mile-wide (96-km-wide) ancient scar on the surface of Ceres.
The white light reflecting from within was revealed as a crater-within-a-crater, which drove NASA scientists to have a closer look.
Between June and October 2018, when Dawn's mission was quickly coming to a close, the spacecraft flew within 22 miles (35 km) of Ceres' surface. This close flyby improved Dawn's imaging resolution by a factor of 10, according to Castillo-Rogez — providing planetary scientists with an unprecedented glimpse of the geology and composition of the Occator area.
Bright spots on Ceres
Ceres' crater Occator has a bright spot, and it's crucial to grasp the nature of the dwarf planet, reports CNET. Called Cerealia Facula, earlier research suggested the reflective sheen was happening because of salt residues dispersed across the surface — which points to past water activity. As to how and when water came to rest in the Occator crater-within-a-crater, two competing theories were at-hand.
The first idea supposed that salty residues came from the impact responsible for the crater, but the second one hypothesized that fluids might still bubble up from beneath the surface of Ceres. When Dawn made its close flyby, one study found, the spacecraft found evidence of a "smoking gun," as Castillo-Rogez put it: hydrohalite.
Hydrohalite on Ceres means underground water
Comprised of sea salt (sodium chloride) encapsulated in water molecules, the images from Dawn's infrared mapping device revealed the presence of hydrohalite — thanks to the work of Italian and U.S. researchers.
This is the first time hydrohalite has been discovered beyond Earth.
Understandably, Castillo-Rogez calls the find a "major discovery," adding that it must have only recently come to the surface, likely "less than around 100 years ago." This is robust evidence that there's still liquid on Ceres today, she said. But whether this is a Ceres-wide ocean or simply the persistence of a few lucky pockets of liquid as yet remains unknown.
Mapping liquid on a dwarf planet, how liquid formed
Combined with gravitational data from Occator and the surrounding area, Dawn scientists mapped out the geometry of the underground reservoir of liquid. Two further studies showed researchers analyzing the bright spot's thickness, and calculate its age.
The composition pegs Cerealia as substantially younger than the impact crater. It's probably the result of an impacting body that once smashed into the dwarf planet, forming the Occator crater roughly 22 million years ago, reports CNET.
After this colossal impact, a little "melt chamber" of liquid came into being, and the salty liquid inside then moved upward and surfaced to form the Cerealia structure roughly two million years ago.
As planetary scientists search distant exoplanets for the presence of conditions favorable to life, it's more than welcome news to learn that liquid water — one of the basic conditions for life — is present on the dwarf planet Ceres — in the asteroid belt beyond Mars.