New Hubble Space Telescope images of Ceres, the largest known asteroid, suggest that the body could hold more fresh* water than the planet Earth. Analysis of 267 photographs of the asteroid indicate that it could be mostly ice, wrapped around a rocky core and coated with a thin dusty crust.
With a diameter of around 930km, Ceres is big enough that its shape is affected by its gravity, making it roughly spherical. Previously, scientists thought the asteroid would be fairly uniform in density, as no-one thought it had been heated enough to create layers of different materials.
But the analysis performed by the Cornell researchers suggests exactly the opposite. Computer models suggest that the denser components of the asteroid are collected in its centre, with the lighter ingredients, like water, lying closer to the surface.
Speaking to Space.com, co-author of the study Joel Parker explained: "The most likely scenario from the knowledge we have on how other objects form, it probably has a rocky core and a mantle. That mantle is probably some watery, icy mix, with other dirt and constituents."
He said that the mantle could be as much as a quarter of the entire body's mass, and that if just a quarter of the mantle was water, the asteroid would have around five times more fresh H2O on board that our planet does.
The findings are set to reignite the debate of how a planet should be defined - something that comes up with alarming regularity whenever Pluto is mentioned. This is because all the nine (or eight, plus Pluto, depending on your perspective) planets have differentiated interiors, like Ceres.
Lucy McFadden, one of the researchers making the observations, suggests that Ceres be considered an embryonic planet: "Gravitational perturbations from Jupiter billions of years ago prevented [it] from accreting more material to become a full-fledged planet," she says. ®
*A clarification. Our thanks to the readers who wondered "is that fresh, or salty water?"