Tech UPTechnologyCeres' water volcanoes could still be active

Ceres' water volcanoes could still be active

 

When we think of volcanoes, we usually think of red-hot magma, molten rock, and gases laden with sulfur and other compounds unfriendly to life. It makes sense, because after all terrestrial volcanoes are like that: they expel the materials that abound under the earth’s crust . However, in other bodies of the solar system or the universe this does not have to be the case. For example, we know that the surface of the Jovian moon Europa is largely made of water ice , or that Pluto’s mountains are made, in part, of this same material. However, at the usual temperatures on those worlds, the ice does not behave as it does on Earth . There, this material is as hard as terrestrial rocks.

Similarly, we know that the dwarf planet Ceres , the largest body in the asteroid belt between Mars and Jupiter, is largely made up of water ice . Recent investigations, carried out thanks to information and photographs collected by NASA’s Dawn probe, have shown that this dwarf planet could continue to show geological activity and volcanism . Not only that, but with high probability, this volcanism involves the expulsion of liquid water to the surface, in the form of highly saline mud .

Ceres is a dwarf planet, because despite directly orbiting the Sun and having enough mass to have acquired a spherical shape, it has not been able to clear its orbit of other smaller bodies . These smaller bodies, numbering in the millions, form the asteroid belt, which dominates (although not absolutely) Ceres. This body is about 940 kilometers in diameter (for comparison, the diameter of the Moon is about 3,500 kilometers) and orbits on average almost three times farther from the Sun than the Earth . It is the only dwarf planet whose orbit is completely within the orbit of Neptune and was in fact discovered before this icy giant, in 1801 by the Italian Giuseppe Piazzi .

 

Since then it has been observed countless times, with increasingly powerful telescopes, including the Hubble Space Telescope and the Keck Observatory Telescope in Hawaii. However, until the arrival of the Dawn probe to the dwarf planet in 2015 , we did not have any images that would allow us to study its surface in detail. Since then, many investigations have studied the multitude of craters that populate Ceres, some of them obtaining evidence of past cryovolcanism . This new study (A. Nathues et al, 2022) shows evidence of volcanism that occurred a maximum of 250 million years ago , and that it could still be active today .

Thanks to data collected by the Dawn probe, we know the internal structure of Ceres in some detail. It has a thin surface layer of regolith , as does our Moon, made up of small rock fragments, dust, and sand. This regolith rests on a thick crust formed by different types of ice (with a large presence of water ice), several tens of kilometers thick. Under this crust there would be a thin layer of highly salty mud , or brine, also composed mainly of water and that would be the material ejected in recent eruptions. Beyond this liquid layer would be a denser mantle composed of solid rock and heavier metals .

Nathues’ team has studied the region of the Urvara crater , a crater located in the southern hemisphere of Ceres, with a diameter of more than 100 kilometers and a depth of more than six kilometers with respect to the mean level of Ceres . This depth makes Urvara a perfect region to study the crust of this star . The crater was formed about 250 million years ago by the impact of a smaller body, probably from the asteroid belt itself. In their research they have identified that part of the base of the crater is younger than the rest of the structure, having been formed about 100 million years after the collision . This time is much longer than it would take for the area to cool down after the heat released by the impact, so its origin should be the result of volcanic activity in the area.

In addition, spots that are much lighter than the surrounding terrain have been observed and that seem to flow down the crater , which also have a high salt content. The hypothesis therefore is that these salts reached the surface from a geyser-type volcanic eruption of the mud that resides in the depths of the dwarf planet and that the water, in the absence of an atmosphere, quickly evaporated leaving behind the solid compounds in suspension . The presence of these salts would help the water to remain liquid despite Ceres’s low internal heat. A solution of salt in water can lower its melting temperature considerably . This is the physical rationale behind the mundane fact that we salt our streets, sidewalks and highways when it snows. The salt does not heat the snow, but rather lowers its freezing temperature, making it liquid even when temperatures are below 0°C.

REFERENCES:

A. Nathues et al, 2022, Brine residues and organics in the Urvara basin on Ceres, Nat Commun 13, 927, https://doi.org/10.1038/s41467-022-28570-8

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