Scientists are attributing the mysterious bright spots on Ceres, the largest object on the main asteroid belt, to a giant reservoir of salt water beneath the dwarf planet’s crust.
Oceans beneath the surface are the kind of things we expect to see in the outer solar system, especially icy moons in orbit around Jupiter, Saturn, Uranus, and Neptune. But according to seven (yes, seven) new newspapers published for a particular Nature collection, sub-surface oceans can also appear in objects without a host planet, as shown by Ceres, a dwarf planet in the main asteroid belt between Mars and Jupiter.
Ceres, as new research shows, was recently active and may still be, containing a large reservoir of groundwater and exposure to a form of cryovolcanism (in which groundwater reaches the surface) not seen in an object heavenly. Oceans beneath the surface 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 of the planet’s fewer objects in the asteroid belt. In Ceres, this phenomenon is more a matter of chemistry, as the water below the surface remains in a clumsy state due to its high salt content.
The new research, described in papers published in Nature Astronomy, Nature Geoscience, and Nature Communications, involves scientists from NASA, the Lunar and Planetary Institute (LPI), the University of Münster in Germany, the National Institute of Science and Education (NISER)) in India, among many other institutions.
At 590 miles wide (950 kilometers), Ceres is the largest object in the asteroid belt. NASA’s Dawn spacecraft visited Ceres from 2015 to 2018, gathering very important data during the last five months of the mission, when the orbiter moved to 22 kilometers (35 km) of the surface.
High-resolution images returned to Earth revealed the October crater in unprecedented detail. This crater, formed by a giant impact, is the most distinctive feature of the dwarf planet, measuring 57 miles (92 km) wide, which is pretty large even by Earth standards. Crater Hour was discovered as a complex structure, representing a central depression covered in a similar structure with various domes, cracks and grooves, and bright mineral deposits and smaller domes scattered throughout.
That water may have been responsible for Ceres’s bright surface features was suspected before the Dawn mission, but data collected by the orbiter suggests this is highly coincidental.
A number of low-impact craters in Ceres indicate a relatively new surface. Oxator Crater was formed about 22 million years ago, with some of the newest surface features in Ceres forming just 2 million years ago.
A common feature of impact craters is a canopy that forms in the center. Such a characteristic was formed in the Interior, but it collapsed, creating a depression within the depression. Then, about 7.5 million years ago, water – or rather a brine – rose to the surface, flowing to this collapsed peak. This salt water evaporated, leaving behind reflective deposits in the form of sodium carbonate – a mixture of sodium, carbon and oxygen. The bright white splotch in the center of Occator, Cerealia Facula, is the remnant of this process.
Similar deposits appear elsewhere within the crater, including a prominent feature called Vinalia Faculae. In these places, brine rose to the surface through cracks and furrows.
About 2 million years ago, Cerealia Facula became active again, extracting more brine, forming a central dome of a bright material. These processes were ongoing about 1 million years ago, and they can still occur today, although cryovolcanic processes have weakened significantly over time.
Evaporation and sublimation (when liquid turns directly into gas) forced water to the surface, in a form of crovolcanism not seen anywhere else in the solar system, according to the researchers. Scientists have a good reason to believe that this process may exist elsewhere in other seemingly inert bodies.
“Evidence for very recent geological activity in Ceres contradicts the general belief that small bodies in the solar system are not geologically active,” said Guneshwar Thangjam, co-author of Natural Astronomy. paper and a researcher from NISER, in a Press release.
Most importantly, the ocean beneath the surface is likely to form as a result of the impact event created by the Craterator, but its constant slowness is due to salt dissolved in groundwater.
“For the large deposit at Cerealia Facula, most of the salts were supplied from a humid area just below the surface that melted from the impact heat that formed the crater about 20 million years ago,” said Carol Raymond, first author of Astronomy nature survey and Chief Dawn investigator, said in a NASA Press release. “The heat of impact diminished after a few million years; however, the impact also created large fractures that could reach the deep, long-life reservoir, allowing brine to continue to penetrate the surface. “
Ceres contains hundreds and possibly thousands of smaller deposit sites, most of which are thicker than 33 meters (10 meters) thick. Domes and pits appear on the surface, also formed by the movement of groundwater.
By studying the weight of Ceres, scientists were able to ascertain its internal structure. The salt reservoir lies about 40 miles (40 km) below the surface and is hundreds of miles wide. Given that Ceres himself is only 590 miles wide, it is fair to call Ceres an oceanic world.
It seems overnight, Ceres has become a tremendous target for astrobiologists. With its complex chemistry, liquid water, and constant surface and subsurface dynamics, it may have been habitable at some point during its recent history. A mission to send a probe to the surface suddenly seems like a very good idea.