The Icy Secrets of Ceres

New research suggests water ice lurks under the surface of the dwarf planet.


Before NASA put a spacecraft inside the orbit of Ceres, the dwarf planet looked to astronomers like a pixelated gray button with mysterious bright spots.

The Dawn probe, which arrived at Ceres last March, revealed through high-resolution images a rocky, smog-colored world pockmarked by craters. It zeroed in on those white, chalk-like spots, which scientists now believe are salt deposits, left behind when water ice, exposed after a crater-causing collision, evaporated. The spots led scientists to look for other parts of Ceres where water ice may hide, like regions that exist in perpetual shadow, out of reach of direct sunlight.

These were good places to look, according to a pair of studies published Thursday. Using data from Dawn’s spectroscopic instruments, researchers have detected water ice in a bright spot found in the floor of a crater that exists in perpetual cold and darkness, according to a study in the journal Nature Astronomy. Researchers identified more than 600 craters that don’t receive direct sunlight, which means the conditions of stable water could exist in more.

A separate team of researchers, using Dawn’s neutron and gamma-ray detectors, have concluded that a layer of water ice sits just one meter beneath the surface of the dwarf planet, according to a study in the journal Science. The ice, they say, is concentrated in Ceres’s polar regions, which receive less sunlight than other areas.

Both teams’ work builds on research that suggests conditions on Ceres have allowed it to retain lots of water beneath its surface for as many as billions of years. It also suggests water ice can survive on other objects like Ceres, whose classification hovers between dwarf planet and overgrown asteroid. But Ceres’s water is not likely to be liquid, even further down. Researchers believe that if liquids exist in the subsurface, they’re probably some kind of briny fluids.

Aside from Ceres, water ice has been detected on the moon, Mercury, Pluto and on the moons of Jupiter and Saturn, suggesting its presence is common in the solar system. The presence of water on Ceres was first detected from Earth in 2014, when the European Space Agency’s now-retired Herschel space telescope spotted plumes of vapor erupting on Ceres. But Dawn’s instruments have provided further proof of water—and where it may be hiding.