Although today we see the dwarf planet Ceres as a cold, rocky world quietly floating in the main asteroid belt between Mars and Jupiter, the latest scientific discoveries based on data from a NASA mission paint a significantly different and more dynamic past. New research indicates that this celestial object, the largest in its neighborhood, may have once possessed a deep and long-lasting energy source, a key ingredient that could have maintained conditions suitable for life. Although there is no direct evidence of the existence of microorganisms, these findings strongly support theories that Ceres could have been habitable for single-celled life forms in its distant past.

The search for the recipe of life

The search for life beyond Earth is guided by the quest for three key elements that we consider essential. The first is, of course, liquid water, the universal solvent that enables the chemical reactions necessary for biology. The second is organic molecules, complex carbon-based compounds that form the building blocks of life as we know it. The third, often overlooked but equally crucial, is an energy source that living organisms could use to sustain their metabolism. The latest study, published yesterday in the journal Science Advances, sheds new light on precisely this third element on Ceres, suggesting that a stable source of "food" for potential microbes existed there.

An ocean hidden beneath an icy crust

The story of Ceres' potential habitability began thanks to revolutionary data collected by NASA's Dawn spacecraft. The mission, which ended in 2018 after running out of fuel, conducted detailed investigations of this dwarf planet. One of the most spectacular discoveries was the extremely bright, reflective spots on its surface, particularly within the Occator crater. Detailed analysis showed that these are salt deposits, predominantly sodium carbonate, left behind after liquid from the interior erupted onto the surface and evaporated into the vacuum of space.

This was a clear indicator of the existence of liquid below the surface. Further research, published in 2020, confirmed that beneath Ceres' icy crust lies a huge reservoir of salt water, or brine. This discovery confirmed the presence of the first key ingredient for life – liquid water. Ceres thus joined the exclusive club of celestial bodies in our Solar System, such as Jupiter's moon Europa and Saturn's moon Enceladus, which are believed to hide oceans beneath their icy surfaces.

The building blocks of life and an ancient energy engine

The Dawn mission did not stop at the discovery of water. Instruments on the spacecraft also detected the presence of organic materials on Ceres' surface. These are carbon-based molecules, which are absolutely necessary for the formation of life. Although not proof of life in themselves, their presence confirmed that Ceres also had the second key ingredient from the recipe for habitability. Thus, two of the three elements were confirmed, but the question of an energy source remained open.

The latest study finally offers an answer to that question. A team of scientists created sophisticated thermal and chemical models to simulate the conditions inside Ceres over billions of years. Their results show that approximately 2.5 to 4 billion years ago, Ceres' rocky core was significantly warmer than it is today. The heat came from the decay of radioactive elements within the rocks, a process known as radiogenic heating, which was common in the early stages of the Solar System's formation.

This internal heat drove a process similar to what we see on Earth at hydrothermal vents on the ocean floor. Hot water, enriched with dissolved gases and minerals from the rocky core, traveled upwards and mixed with the colder water of the subsurface ocean. This process, known as rock metamorphism, released molecules like methane and carbon dioxide – powerful sources of chemical energy.

“On Earth, when hot water from the deep mixes with the ocean, the result is often a real buffet for microbes – a feast of chemical energy,” explained Sam Courville, the study's lead author. In other words, ancient Ceres could have had a steady supply of hydrothermal fluids that supplied its subsurface ocean with nutrients, thereby creating a potentially habitable environment independent of sunlight.

A window into the past and a comparison with other worlds

Today, Ceres is likely too cold to support life. Its internal radioactive engine cooled over time, and the remaining liquid became highly concentrated and salty. The period of greatest potential for habitability was in its "youth," about half a billion to two billion years after its formation, when the rocky core reached its temperature peak. This was the moment when the flow of warm, energy-rich fluids into the subsurface ocean was most intense.

Unlike moons such as Europa and Enceladus, which still have active oceans today thanks to the gravitational forces of their parent planets (Jupiter and Saturn) that constantly "knead" and thus heat them from within, Ceres does not have this luxury. Its heat source was exclusively internal and time-limited. Because of this, its window for habitability was in the distant past.

Nevertheless, this discovery has huge implications for the search for life. It suggests that many other icy bodies of similar size (Ceres has a diameter of about 940 kilometers) throughout the outer Solar System, which do not have significant heating caused by planetary gravity, may also have a similar past. Perhaps they too, at one point in their history, had warm, chemically rich oceans hidden beneath the ice, offering a chance for life to emerge. This dramatically expands the list of places where we might look for traces of ancient life, showing that even lonely dwarf planets in the asteroid belt can hide surprising secrets.