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NASA research has found that the dwarf planet Ceres may have had a deep, long-lived chemical energy source that may have sustained habitable conditions in the past, NASA reports.
In this sense, this source of chemical energy comes from the types of molecules needed to fuel certain microbial metabolisms. Although there is no evidence of the existence of microorganisms on Ceres, the discovery supports theories that this planet, the largest body in the main asteroid belt between Mars and Jupiter, may have once harbored conditions conducive to unicellular life.
However, this result does not mean that Ceres harbored life, but rather that "food" would likely have been available if life had arisen on Ceres, notes the research, published this week in Science Advances.
In this regard, scientific data from NASA's Dawn mission, which ended in 2018, showed that the bright, reflective regions on Ceres' surface were composed of residual salts from liquid that seeped from the subsurface.
A subsequent 2020 analysis revealed that the source of this liquid was a vast reservoir of brine, or salt water, beneath the surface. In another study, the Dawn mission also revealed evidence that Ceres contains organic matter in the form of carbon molecules, essential, though not sufficient on its own, for the sustenance of microbial cells.
In the current study, the authors built thermal and chemical models that simulate the temperature and composition of Ceres' interior over time. They found that about 2.5 billion years ago, Ceres' subsurface ocean may have had a steady supply of warm water containing dissolved gases rising from the metamorphosed rocks of the rocky core. The heat came from the decay of radioactive elements in the dwarf planet's rocky interior, which occurred during Ceres's youth—an internal process thought to be common in the solar system, they said.
The study's lead author, Sam Courville, explained that "on Earth, when warm water from deep underground mixes with the ocean, the result is often a feast of chemical energy for microbes." Therefore, determining whether Ceres' ocean received an influx of hydrothermal fluid in the past "could have important implications," he added.
However, the Ceres we know today is unlikely to be habitable, as it is colder, with more ice and less water than in the past. Currently, the heat from radioactive decay on Ceres is "insufficient" to prevent the water from freezing, and the remaining liquid has become concentrated brine, the NASA study emphasizes.
The research therefore suggests that the period when Ceres would likely have been habitable was between 500 and 2 billion years after its formation (or between 2.5 and 4 billion years ago), when its rocky core reached its maximum temperature. This was when warm fluids were introduced into Ceres's groundwater.
The dwarf planet also doesn't benefit from the current internal heating generated by the push and pull of orbiting a large planet, unlike Saturn's moon Enceladus and Jupiter's moon Europa. Therefore, Ceres's greatest potential for generating energy that would make it habitable was already in the past.
This result also has implications for water-rich objects in the outer solar system, as many of the other icy moons and dwarf planets similar in size to Ceres (about 940 kilometers across) that do not experience significant internal heating due to the gravitational pull of the planets could also have had a period of habitability in the past.
