At first glance, the dwarf planet Ceres hardly inspires dreams of alien life. Orbiting between Mars and Jupiter in the asteroid belt, it is a frigid, gray world, battered and cracked. Its surface temperatures swing between a bracing –93°C to –33°C. There is no atmosphere to speak of, and its gleaming white patches are not signs of life—but salt, likely left behind by ancient brines that once seeped to the surface.

But in a new study published in Science Advances on August 20, researchers offer a radically different view of Ceres’s ancient past. Beneath the frozen shell, they argue, there may have once been an ocean warmed from within by the steady pulse of a radioactive heart. This core could have been capable of generating chemical energy for hundreds of millions of years. Enough, perhaps, to sustain life.

The Warm Heart of a Cold World

The idea that Ceres once harbored a subsurface ocean isn’t new. NASA’s Dawn mission, which orbited the dwarf planet from 2015 to 2018, revealed evidence of an ancient briny reservoir hiding under a shell of ice. It also found carbon-based organic molecules—one of the key ingredients for life—and bright salt deposits scattered across the surface, signs that liquid once percolated upward.

What the new research adds is the final piece in the habitability puzzle: a long-lasting internal energy source.

“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,” said Sam Courville, a planetary scientist at Arizona State University and lead author of the new study. “So it could have big implications if we could determine whether Ceres’ ocean had an influx of hydrothermal fluid in the past.”

To investigate this, Courville and colleagues built a model that simulates Ceres’s interior evolution over billions of years. Their aim was to determine whether its rocky core ever got hot enough to trigger metamorphic reactions—those that release gases like hydrogen and carbon dioxide into surrounding water. These molecules can drive redox reactions, providing chemical energy to hypothetical microbes.

The answer was yes. Their model showed that between about 500 million and 2 billion years after Ceres formed (roughly 4 billion years ago), its core likely reached up to 800 Kelvin (around 527°C). This was hot enough to cook the minerals in its core, releasing volatile compounds into a subsurface ocean and setting up redox gradients.

A Feast Underground, Then a Freeze

Chemical energy of this sort is what sustains life around hydrothermal vents on Earth. In these deep-sea environments, microbes feed on the energy generated by the interaction between hot, mineral-rich fluids and cold ocean water. On Ceres, similar conditions could have existed in the past.

The fluids bubbling up from the deep would have carried hydrogen and carbon dioxide—ideal ingredients for methanogenesis, a process some microbes use to turn these molecules into methane and energy. In fact, Courville’s team calculated that a single kilogram of deep pore fluid could have supported up to 3 trillion microbial cells.

“Ceres’s deep pore fluids would have higher concentrations of H₂ and CO₂ compared to the ocean,” the authors write in the paper. “Thus, Ceres’s most habitable period would have been during metamorphism, between ~0.5 and 2 Gyr after formation”. (Gyr=Gigayear, one billion years)

But that window is now closed. The radioactive isotopes that once powered this internal heating—like aluminum-26 and potassium-40—have long since decayed. The subsurface ocean, once potentially teeming with energy, has become a cold and salty slush. Temperatures have dropped below the limit for known terrestrial life.

As the authors put it: “Ceres’s ocean has likely become a cold, concentrated brine with fewer sources of energy, making it less likely to be habitable at present”.

Not Just Ceres

The implications of this study reach beyond one dwarf planet. Ceres is about 940 kilometers wide—small by planetary standards, but typical for many icy bodies in our solar system. Many of these, like the moons of Uranus and some of Saturn’s smaller satellites, share similar size and composition.

“If Ceres was habitable in the past, then probably there are tens of asteroids and moons that were also habitable in the past,” said Joe O’Rourke, a co-author and planetary scientist at Arizona State University, in an interview with New Scientist.

This broadens the search for past habitability beyond just the big names like Europa or Enceladus. Those moons still have tidal heating, generated by the gravitational pull of their massive planetary hosts. But Ceres, being alone in the asteroid belt, relied solely on the heat from its own interior.

What Could Come Next?

Ceres is now dead quiet. It shows no signs of present-day hydrothermal activity, and its ancient ocean has mostly frozen. But scientists aren’t done with it.

The team behind the new study says that if we want to confirm whether Ceres was once habitable, we’ll need to go back. A sample return mission to collect surface salts could reveal isotopic fingerprints left behind by deep interior fluids. These could confirm whether the energy-rich gases predicted in the models actually made it to the surface.

The National Academies’ 2022 decadal survey even recommended such a mission under the theme “Origins, Worlds, and Life.”

For now, scientists see Ceres as a barren world that once had a warmer, more active past. Its interior may have stayed hot long enough to support a deep, dark ocean—one that had the basic ingredients needed for life. There’s no evidence that life ever took hold there, but conditions might have allowed it, at least for a time.