The dwarf planet Ceres has a secret saltwater ocean

The dwarf planet Ceres is shown in false color, with the Occator crater visible.

The dwarf planet Ceres is shown in false color, with the Occator crater visible.
Image: NASA/JPL-CalTech/UCLA/MPS/DLR/IDA.

A team of scientists has attributed the existence of mysterious bright spots on Ceres, the largest object in the asteroid belt, to a gigantic reservoir of salt water beneath the dwarf planet’s crust.

Subsurface oceans are the kinds of things we expect to see in the outer solar system, specifically on icy moons that are in orbit around Jupiter, Saturn, Uranus, and Neptune. But according to seven (yes, seven) new studies published for a special collection of the scientific journal NatureSubterranean oceans can also appear on space objects without a host planet, as has been demonstrated by Ceres, a dwarf planet in the main asteroid belt between Mars and Jupiter.

Ceres, as the new research shows, was recently active and could still be, containing a vast reservoir of groundwater and exhibiting a form of cryovolcanism (in which groundwater reaches the surface) never before seen in a celestial object. Subsurface oceans on icy moons such as Jupiter’s Europa and Saturn’s Enceladus are kept warm by tidal interactions exerted by their host planets, but the same cannot be said for space objects without host planets found in the belt. of asteroids. At Ceres, this phenomenon is more a matter of chemistry, as the groundwater remains in a muddy state due to its high salt content.

False color image showing the interior of Occator Crater.  The pink areas show regions where exposed brine spilled onto the surface of Ceres.

False color image showing the interior of Occator Crater. The pink areas show regions where exposed brine spilled onto the surface of Ceres.
Image: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA.

The new research, described in papers published in Nature Astronomy, Nature Geoscience, and Nature Communications, included scientists from NASA, the US Lunar and Planetary Institute (LPI), the University of Münster in Germany, and the National Institute for Education and Education. Scientific Research (NISER) in India, among many other institutions.

At 946 kilometers in diameter, Ceres is the largest object in the asteroid belt. NASA’s Dawn spacecraft visited Ceres between 2015 and 2018, collecting critically important data during the last five months of the mission, when the orbiter plummeted 35 km from the surface.

High-resolution images sent to Earth revealed the Occator Crater in unprecedented detail. This crater, formed by a giant impact, is the most distinctive feature of the dwarf planet, measuring 92 kilometers wide, which is quite large even by Earth standards. The Occator Crater was revealed to be a complex structure, with a central depression covered by a dome-shaped structure, several cracks and grooves, bright mineral deposits, and smaller domes scattered throughout.

A view of the Occator Crater showing Cerealia Facula (B) and Vinalia Faculae (C).

A view of the Occator Crater showing Cerealia Facula (B) and Vinalia Faculae (C).
Image: Nathues et al., Nature Astronomy.

It was suspected that water may have been responsible for the bright features of Ceres’ surface prior to the mission. Dawn, and the data collected by the orbiter suggests that this is the case.

A count of small impact craters on Ceres points to a relatively young surface. Occator Crater formed about 22 million years ago, and some of the younger surface features on Ceres formed only 2 million years ago.

A common feature of impact craters is a peak that forms in the center. Such a feature formed within Occator, but collapsed, creating a kind of depression within the depression. Then, about 7.5 million years ago, water, or rather brine, rose to the surface and seeped through this collapsed peak. This salty water evaporated, leaving reflective deposits in the form of sodium carbonate, that is, a mixture of sodium, carbon and oxygen. The bright white spot in the center of Occator, called Cerealia Facula, is the remnant of this process.

Similar deposits appear in other parts of the crater as well, including a prominent feature called Vinalia Faculae. In these places, the brine rose to the surface through cracks and grooves.

Close-up views of Cerealia Facula (B) and Vinalia Faculae (C).

Close-up views of Cerealia Facula (B) and Vinalia Faculae (C).
Image: Nathues et al., Nature Astronomy.

About 2 million years ago, Cerealia Facula became active again, shedding mas brine, forming a central dome of shiny material. These processes were ongoing around 1 million years ago, and are possibly still happening today, although cryovolcanic processes have weakened considerably over time.

Evaporation and sublimation (when the liquid transforms directly into gas) forced the water to rise to the surface, in a form of cryovolcanism that has not been seen anywhere else in the Solar System, according to the researchers. Scientists have good reason to believe that this process may exist in other parts of other apparently inert bodies.

“Evidence for very recent geological activity on Ceres contradicts the general belief that small bodies in the solar system are not geologically active,” said Guneshwar Thangjam, co-author of the Nature Astronomy article and NISER researcher, in a Press release.

Importantly, the subsurface ocean likely formed as a result of the impact event that created the Occator Crater, but its ongoing sludge is due to dissolved salt in groundwater.

“For the large Cerealia Facula deposit, most of the salts were supplied from a muddy area just below the surface that melted from the heat of the impact that formed the crater about 20 million years ago,” Carol Raymond, author main of Nature Astronomy study and principal investigator for Dawn, said in a Press release from NASA. “The heat of the impact subsided after a few million years; however, the impact also created large fractures that could reach deep and long-lasting deposit, allowing the brine to continue to seep to the surface. “

Bright white deposits and domes within Occator Crater, formed from groundwater.

Bright white deposits and domes within Occator Crater, formed from groundwater.
Image: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA.

Ceres features hundreds and possibly thousands of deposits mas small, most of which are less than 10 meters thick. Domes and pits appear on the surface, which are also formed from the movement of groundwater.

By studying Ceres’s gravity, scientists were able to infer its internal structure. The salty deposit lies about 40 km below the surface and is hundreds of kilometers wide. Since Ceres itself is only 947 kilometers in diameter, it is possible to call Ceres an ocean world.

Ceres has apparently become a tempting target for astrobiologists overnight. With its complex chemistry, liquid water, and ongoing surface and subsurface dynamics, it may have been habitable at some point in its recent history. A mission to send a probe to the surface suddenly seems like a very good idea.

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