NASA’s Dawn mission and the habitability of Ceres

When NASA’s Dawn mission entered orbit around Ceres in 2015, researchers - and the wider public - were able to see this unusual, striking planetoid in close-up for the first time.

Ceres is the biggest body in the Main Asteroid Belt, representing more than 39 percent of the belt’s total mass. It is also the only object there to have reached hydrostatic equilibrium (in other words, it became spherical because its own gravity pulled it into a round shape).

Between 2015 and 2018, before the spacecraft ran out of fuel, Dawn returned a rich set of observations that highlighted several intriguing aspects of this enigmatic, ice-rich planetoid.

Ceres as an “Ocean World” in Dawn mission research

In the same way that Jupiter’s moon Europa and Saturn’s moons Titan and Enceladus have been discussed, scientists have proposed that Ceres might qualify as an “Ocean World” - meaning it could contain a liquid-water interior that might support life.

Dawn’s results suggested, however, that Ceres’s interior is too cold to keep water from freezing, and that any remaining liquid would most likely exist as concentrated brines. Even so, new work by NASA scientists indicates that Ceres may once have offered suitable conditions for single-celled life roughly 2.5 to 4 billion years ago.

The research was headed by Samuel W. Courville, a Planetary and Earth Scientist at Arizona State University (ASU)’s School of Earth and Space Exploration (SESE). He carried out the work while serving as an intern at NASA’s Jet Propulsion Laboratory (JPL).

He collaborated with several scientists from SESE and JPL, as well as the School of Molecular Sciences at ASU and the Department of Genome Sciences at the University of Washington. Their paper, outlining the results, appeared on 20 August in Science Advances.

Based on Dawn’s measurements, the team determined that Ceres does not generate enough core heat from radioactive decay to sustain an internal ocean. In contrast to Europa, Enceladus, and other “Ocean Worlds”, Ceres also lacks tidal heating - the extra warmth some bodies receive due to the gravitational pull of a nearby giant planet.

Earlier analysis of Dawn data indicated that Ceres’s bright, highly reflective surface areas are mainly made up of salts, thought to be residues left after liquid water seeped upward from a large subsurface reservoir. Separate studies also reported indications of organic, carbon-bearing molecules on the surface.

For this study, the authors built thermal and chemical models designed to reproduce how Ceres’s interior temperature and composition would have evolved over time. The models imply that, 2.5 to 4 billion years ago (around 500 million to 2 billion years after Ceres formed), the subsurface may have been supplied with hot water on an ongoing basis.

This heat would have come from radioactive decay within Ceres’s rocky, metallic core during the planetoid’s early history. Their assessment further indicated that the water carried dissolved gases that rose as bubbles from metamorphosed rocks where the core meets the mantle.

Together, these findings suggest that Ceres once possessed the third and final ingredient required for life, and they also carry consequences for how we think about other water-rich bodies across the Solar System.

Many planetoids similar in size to Ceres (approximately 940 km across; about 585 miles) likewise lack strong internal heat sources driven by radioactive decay, or tidal heating provided by the gravity of massive planets. These findings essentially state that while these bodies may not be habitable today, they may have been in the past.

Courville said in a NASA press release:

On Earth, when hot water from deep underground mixes with the ocean, the result is often a buffet for microbes – a feast of chemical energy. So it could have big implications if we could determine whether Ceres' ocean had an influx of hydrothermal fluid in the past.

This article was first published by Universe Today. Read the original article.