On the dwarf planet Ceres in the past could exist ocean
Ceres in natural colors, snapshot of the Dawn mission of May 2015
In March 2015, the NASA Dawn mission arrived at Ceres, the protoplanet and the largest asteroid belt object. Dawn's mission is exploring the oldest objects in the solar system to get an idea of the conditions and processes that took place at the early stages of its existence. Dawn has already determined that aquifers are common on Ceres, suggesting that there was a global ocean on the protoplanet.
This, of course, caused a lot of questions: what happened to the ocean, and could water still exist on Ceres? In this regard, the Dawn team recently conducted two studies that shed light on these issues. In the first, the gravity data was used to describe the interiors of the protoplanets. In the second, the topography of a celestial body was studied in order to determine its structure.
The first study, "Restrictions on the internal structure of Ceres and evolution based on its shape and gravity, measured by the Dawn spacecraft," was recently published in the Journal of Geophysical Research. The team, led by a post-doc at JPL Anton Yermakov, included researchers from the Goddard Center for Space Flight, German Aerospace Center, Columbia University, University of California at Los Angeles, and the Massachusetts Institute of Technology.
Photo of Ceres, made by Dawn probe.
The team worked with protoplanet gravity data collected by Dawn probe after it entered orbit around Ceres. Using NASA's remote space communications network to track small changes in the orbit of a spacecraft, Yermakov and his colleagues were able to measure shape and gravity on Ceres to determine its composition and structure.
They found evidence of geological activity in Ceres; if not at the present moment, then in a relatively recent past. This can be seen in the three craters - Okkator, Kervan and Yalod - and on the only high mountain of Ceres, Ahuna Mons. They are associated with "gravitational anomalies", discrepancies between the models of gravity of Ceres and the fact that the probe Dawn observes in reality.
The team concluded that these four features and other noticeable geological formations are signs of cryovolcanism of subsurface structures. Moreover, they identified a relatively low density of the crust, which is closer to the ice than to hard rocks. But this did not coincide with a previous study done by Michael Bland of the US Geological Survey.
A study by Bland, published in the journal Nature Geoscience in 2016, noted that ice is unlikely to be the main component of Ceres' dense crust, since it is too soft for that. Naturally, the question arises of how the crust can be as light as ice, coinciding with it in density, and much more durable. To answer this question, the second team attempted to model the evolution of the surface of Ceres.
The gravitational data on Ceres, which provided clues about its structure
Their research, "The internal structure of Ceres, discovered with the help of surface topography and gravity," was published in the journal Earth and Planetary Science Letters. The team led by Roger Fu, an associate professor from the Department of Earth, Atmospheric and Planetary Sciences at MIT, consisted of employees from the Virginia Institute of Technology, the California Institute of Technology, the Southwestern Research Institute, the US Geological Society and the National Institute of Astrophysics of Italy.
They studied the strength and composition of the Ceres bark and the internal structure, based on its topography. Modeling the protoplanet bark flows, Fu and her colleagues determined that it most likely consists of a mixture of ice, salts, stones andclathrate hydrates . Such structures, consisting of a gas molecule surrounded by water molecules, are obtained in 100-1000 stronger than water ice.
According to their theory, such a high-strength structure can rest on a softer layer containing a certain amount of liquid. This allows the Ceres topography to change over time and smooth the features that once stood out more strongly. Also this option answers the question about the possible ocean - it froze and it was tied down by a hard crust. However, part of its waters must still be in a liquid state below the surface.
This theory coincides with several models of thermal evolution, published before Dawn arrived at Ceres. Models claim that there is liquid water inside Ceres, which is similar to finds made on the moon of Jupiter, Europe, and on the moon of Saturn, Enceladus. But in the case of Ceres, this fluid may be remnants of the ancient ocean, and not the result of the current geological activity of the celestial bodies.
Possible internal structure of Ceres
Together, these studies show that Ceres had a long and turbulent history. In the first study, it was found that the bark of Ceres is a mixture of ice, salts and aquifers - representing most of the ancient ocean. The second study suggests that under the tough surface crust of Ceres lies a softer layer, which may be a sign of fluid left over from the ocean.
As Julie Castillo-Roges explained, a participant in the Dawn project at JPL and co-authored both studies: “We are increasingly learning that Ceres is a complex, dynamic world that has had a lot of water in the liquid phase in the past, and its quantity is in the present. ”
On October 19, 2017, NASA announced that the Dawn mission was being extended until the vehicle ran out of fuel — this would happen sometime in the second half of 2018. Renewal means that Dawn will be in orbit around Ceres when it passes through perihelion in April 2018. At this time, the surface ice will begin to evaporate and form a temporary atmosphere.
During this period and further, the device will remain in a stable orbit around Ceres, and will continue to send information about this protoplanet. The findings will help improve our understanding of the early stages of the development of the solar system and its evolution over billions of years.
In the future, perhaps, we will send an apparatus to Ceres, which will be able to descend to its surface and explore its topography directly. If everything works out, in the future, missions will be able to explore the insides of Ceres, as well as other “oceanic” worlds like Europe and Enceladus, and find out what lies beneath their icy surface!