Scientists considered Pluto a planet when it was discovered, but it later became the first dwarf planet. However, it is not the closest to Earth. Ceres is a dwarf planet and the largest object in the Great Asteroid Belt, and it has a new distinction today: ocean world. The latest data from NASA’s Dawn mission proves that the near-planet has an enormous repository of salt water hidden beneath its surface. That makes it a possible home for life in the solar system.
NASA’s ion-powered Dawn spacecraft visited Ceres in 2018, and came as close as 35 kilometers from the surface. Images of Dawn’s approach aroused interest when she showed several bright spots in the 57-mile (92-kilometer) Occator Crater. The entire asteroid is only 990 km (diameter), so this crater is quite prominent.
Researchers working on the Dawn mission used geomorphology and topographic data to trace the origin of the spots once and for all. We now know that the bright spots are a result of salt crystallization on the surface, and these deposits are young – from within the last few million years. The high saline solution would evaporate in a few hundred years, but the crater itself is about 22 million years old. Scientists know that the salt deposits are younger, because Ceres is often hit by smaller asteroids that would obscure the reflective surfaces over time.
This image with false colors of Dawn highlights the salt that has recently been shed.
The team identified two sources of salt deposits on Ceres. The first was a slushy pool of brine just below the surface. Ceres has no internal geological warming, but the impact formed by Occator Crater liquidated the water. That puddle cooled after a few million years, but the impact also produced fractures that extended deep into the surface. The fractures cross a larger, long-lived reservoir of brine further downward. Over time, this allowed more brine to seep to the surface where it evaporated and left more salt behind.
That, Ceres is an ocean world, at least to some degree. All we can say right now is that their reservoir of salt water is regional, but it might be more extensive. This raises the question of whether life could survive on Ceres. The high salinity may not be pleasant for most organisms, but there are hearty microorganisms on Earth that love the extremely high levels of salt. Maybe there’s something like that living in the oceans of Ceres.
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