Dwarf planet Ceres is a water world

Nasa's Dawn mission discovered telltale signs of underground ocean on Ceres before spacecraft's journey to asteroid belt ended in 2018

A view of the dwarf planet Ceres obtained by NASA's Dawn spacecraft. Reuters

Subterranean oceans have been discovered on the nearest dwarf planet to Earth, according to new research published on Monday.

Analysis of data from a US space mission suggests the presence of an extensive brine reservoir deep beneath the surface of Ceres, the largest object in an asteroid belt between Mars and Jupiter.

The findings suggest that Ceres – which was once thought to be a barren space rock – was geologically active in the relatively recent past, according to an article the Nature Astronomy journal.

The discovery is based on information sent back from Nasa's Dawn spacecraft, which orbited Ceres from 2015 to 2018 before it ran out of fuel.

Ceres, which was discovered in 1801, has its own gravity, which enabled Dawn to orbit and capture high-resolution images of its surface.

The spacecraft was able to move within 35 kilometres of the asteroid and send back pictures focused on a 20-million-year-old crater. Scientists then determined that there was an "extensive reservoir" of brine beneath its surface.

Using infrared imaging, one team discovered the presence of the compound hydrohalite, a material common in sea ice but which had never before been seen off of Earth.

Maria Cristina De Sanctis, from the Istituto Nazionale di Astrofisica in Rome, said hydrohalite was a clear sign Ceres used to have seas. “We can now say that Ceres is a sort of ocean world, as are some of Saturn's and Jupiter's moons,” she said.

The team said the salt deposits looked like they had built up within the past two million years. Julie Castillo-Rogez from the California Institute of Technology's Jet Propulsion Laboratory said the discovery of hydrohalite was a "smoking gun" for ongoing water activity.