An astonishingly complex world is emerging: New results from NASA’s Dawn mission suggest that there are remains of an underground water reservoir beneath the surface of the dwarf planet Ceres, which is still causing cryovolcanism. In the “Occator” impact crater, highly salty liquid seeps out The results of the investigation show that the substrate rises to the surface and causes light-colored deposits.
With a diameter of around 950 kilometers, Ceres is the largest chunk in the asteroid belt between Mars and Jupiter. While other celestial bodies in this zone often have a strongly dented shape, the comparatively strong gravitation gives Ceres an almost spherical shape. To enable a more detailed look at this exotic world, the dwarf planet was targeted by NASA’s Dawn probe between 2015 and 2018. The recordings have already shown that Ceres has extremely complex structures compared to the other celestial bodies in the asteroid belt.
A nerd in sight
Now the current results are finally making the dwarf planet a celebrity in our solar system. They are largely based on the measurement data from the final phase of the Dawn mission: in the past five months, the probe has approached the surface of Ceres up to 35 kilometers. This resulted in particularly detailed images of the interesting surface structures. In a series of publications in the journals Nature Astronomy, Nature Geoscience and Nature Communications, scientists are now reporting on the results of the analysis of the Dawn data.
The focus of the scientists’ attention was the Occator – an impact crater around 92 kilometers wide in the northern hemisphere of Ceres. Its special feature is a partially bright white color, which has previously given rise to suspicions that there may be traces of water deposits. “If you look closely, the Occator crater has a very complex structure with elevations, depressions, deposits, cracks and furrows. This only became clear in all details in the last phase of the mission, ”says Andreas Nathues from the Max Planck Institute for Solar System Research in Göttingen, who led the camera team for the Dawn mission. He and his colleagues examined the history of the crater when analyzing the data. “We can reconstruct its formation from the current morphology of the crater – and thus take a look at the eventful past of Ceres,” says Nathues.
Traces of cryovolcanism
Based on characteristic features, they came to the conclusion that a large impact created the Occator crater about 22 million years ago. As can be seen from the modeling, a central mountain was created, which collapsed again after a while. About 7.5 million years ago, under its remains, highly salty liquid rose from the interior of Ceres through the cracks in the impact area to the surface. The water of this brine then evaporated and the salts were deposited. This is how the scientists explain the formation of the striking, bright deposits in the center of the Occator crater.
In the following time there were other activities that led to deposits
in the area of the crater floor. About two million years ago, however, the center of the crater woke up again particularly intensely, according to the analyzes. Once again, brine penetrated the surface through the cracks in the crater and created a dome made of light-colored material. “This process should have lasted at least a million years ago,” says Nico Schmedemann from the Westphalian Wilhelms University (WWU) in Münster. “What is particularly remarkable is how long the Occator crater was and possibly still is,” says Nathues.
He and his colleagues believe it is unlikely that the leaked fluid was solely due to melt water from the original impact. Because the warmth that arises from such an impact could not have stayed inside for so many millions of years. And the cause of the cryovolcanism in some of the icy moons in our solar system is also out of the question. They generate heat inside as they are kneaded by the gravitational forces of their mother planets. But the isolated orbiting dwarf planet Ceres does not have this effect.
Liquid bubble in depth
Instead, the results suggest that deep beneath the Occator crater there are remains of a body of water that have been saved from freezing due to their high salt content – similar to the effect of road salt. This interpretation is supported by analyzes of the Ceres gravitational field carried out by a team led by NASA’s Jet Propulsion Laboratory. The researchers present evidence that a bubble of liquid brine could lie about 40 kilometers below the Occator crater. Liquid may still rise from there, seep from the surface and evaporate.
It was previously suspected that Ceres was giving off water, because a kind of thin haze appeared over the Occator crater. The results of Dawn’s spectrometer team, headed by the Institute for Astrophysics and Cosmology in Rome, now provide new information: The researchers were able to identify salt compounds that contain water in the bright, deposited material in the crater. As they explain, this only slightly bound water would have to evaporate on the surface of Ceres within weeks. That means: the deposits cannot be old.
“We assume that Ceres is still occasionally active in cryovolcanoes,” concludes Nathues. But there has probably only been powerful eruptions once – the scientists suspect that water now only escapes through evaporation. “According to the current state of knowledge, such a cryovolcanism is unique in the solar system,” says Schmedemann. The bottom line in the investigation results of the Dawn mission is that Ceres forms a very special world in the solar system, the secrets of which now need to be further uncovered.
Source: Max Planck Institute for Solar System Research
Articles:
Andreas Nathues, Nico Schmedemann, Guneshwar Thangjam et al .:
Recent cryovolcanic activity at Occator on Ceres,
Nature Astronomy, August 10, 2020
Carol A. Raymond et al .:
Impact-Driven Mobilization of Deep Crustal Brines on Dwarf Planet Ceres,
Nature Astronomy, August 10, 2020
Paul Schenk et al .:
Impact heat driven volatile redistribution at Occator crater on Ceres as a comparative planetary process,
Nature Communications, August 10, 2020
Britney Schmidt et al .:
Post-impact cryo-hydrologic formation of small mounds and hills in Ceres’s Occator crater,
Nature Geoscience, August 10, 2020