Scientists Have Discovered Water Ice Hiding in Ceres’ Shadows
published during a full moon.

You never know what might be hiding in the shadows. There’s a vast empty space between Mars and Jupiter that’s peppered with rocky, icy remnants of the early solar system. This is the asteroid belt, and the largest object here is Ceres, a dwarf planet about the size of Texas.


Ceres Carters: An animation of Ceres’ northern craters where the sun really doesn’t shine. Credit: Thomas Platz, et. al.

Though Ceres was discovered in 1801, we hadn’t gotten a lot of new information about the mysterious dwarf planet before 2015, when the Dawn mission started making observations.

Discovered Water Ice

The craters Takel and Cozobi are featured in this image of Ceres from NASA’s Dawn spacecraft. Takel is the young crater with bright material on the left of this image, and Cozobi is the sharply defined crater just below center. Credit: NASA

As described in a newly published paper in Nature Astronomy, researchers looking at photos sent back by Dawn noticed that about 600 of Ceres’ many craters were shrouded in constant shadow–so deeply so that their bases were never lit by the sun. Ten of these craters had curious bright spots located in their depths. The scientists took a closer look to see what was going on in there.

Discovered Water Ice

The small, bright crater Oxo (6 miles, 10 kilometers wide) on Ceres is seen in this perspective view. The elevation has been exaggerated by a factor of two. The view was made using enhanced-color images from NASA’s Dawn mission. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/PSI

Turns out that those bright spots in the dark may contain water ice. The researchers think the water ice could have entered the craters in one of two ways.

Discovered Water Ice

Permanently shadowed regions capable of accumulating surface ice were identified in the northern hemisphere of Ceres using images taken by NASA’s Dawn mission combined with sophisticated computer modeling of illumination. Credit: NASA/JPL-Caltech

One possibility is that the ice formed when the icy interior of Ceres erupted in a cryovolcano–a volcano spewing ice (instead of lava) over a large enough area that some of it got into the craters. That’s a real possibility since a cryovolcano half the size of Mount Everest has been identified on Ceres’ surface. But the ice could also have gotten there in the same way the craters themselves were created–when an asteroid slammed into the dwarf planet’s surface, kicking up water ice that then landed in the craters and stayed there.

Discovered Water Ice

Dawn at Ceres: The Dawn Spacecraft arriving at Ceres in this artist’s interpretation. Credit: NASA/JPL-Caltech

The presence of water ice in the craters is exciting because the same observations have been made on other bodies in the solar system, including Mercury and the Moon. This finding has important implications for future space travel, since knowing where to find sources of water will be critical for refueling astronauts’ bodies as well as their spaceships during extended missions.