Scientists say the brightest spot on surface of the dwarf planet Ceres has the highest concentration of carbonate minerals they’ve ever seen beyond Earth – and that suggests that liquid water welled up from below, mere millions of years ago.
The findings, published online today by the journal Nature, represent a shift in the story explaining Ceres’ mysterious bright spots. Those spots are the most fascinating features on the solar system’s smallest known dwarf planet, which also ranks as the biggest object in the main asteroid belt between Mars and Jupiter.
Updated readings from NASA’s Dawn spacecraft, which is currently circling Ceres, indicate that sodium carbonate is the dominant constituent of the bright patch that’s piled up in the middle of 57-mile-wide Occator Crater.
“This is the first time we see this kind of material elsewhere in the solar system in such a large amount,” study lead author Maria Cristina De Sanctis said in a NASA news release. De Sanctis is a researcher from the National Institute of Astrophysics in Rome and principal investigator for Dawn’s Visible and Infrared Mapping Spectrometer, or VIR.
On Earth, sodium carbonate and similar salts are associated with hydrothermal environments, where heated water wells up from our planet’s crust. Its presence in Occator Crater’s dome of pushed-up material suggests that a similar process occurred on Ceres, potentially helped along by an asteroid impact.
That scenario, in turn, suggests that liquid water must have existed beneath Ceres’ surface millions of years ago.
“The minerals we have found at the Occator central bright area require alteration by water,” De Sanctis said. “Carbonates support the idea that Ceres had interior hydrothermal activity, which pushed these materials to the surface within Occator.”
The best explanation is that the water froze on the surface and then turned to vapor, leaving the carbonates and other bright salts behind. That meshes with earlier studies that detected water vapor emanating from Ceres.
De Sanctis and her team also saw signs of ammonia-bearing salts, such as ammonium chloride and ammonium bicarbonate. That adds to the intrigue: Ammonia and carbonates are among the chemicals detected in the plumes of water ice spewing from geysers on Enceladus, an ice-covered moon of Saturn. The fact that similar chemicals exist on Ceres should perk up the ears of astrobiologists.
“We will need to research whether Ceres’ many other bright areas also contain these carbonates,” De Sanctis said.
A study published by Nature last December, based on readings from Dawn’s framing camera, suggested that the bright spots contained a type of salt known as hydrated magnesium sulfate, or hexahydrate. The newly published findings from VIR point to sodium carbonate as a better match.
De Sanctis is among 28 authors of the Nature paper, titled “Bright Carbonate Deposits as Evidence of Aqueous Alteration on (1) Ceres.”