Ceres — the dwarf planet that has kept the world on tenterhooks with each new image from NASA ’s Dawn spacecraft — is still an odds-on favorite to harbor past or even present microbial life, says the mission’s principle investigator.
The mysterious bright spots in its Occator crater, however, are now thought to be evaporated brine deposits coughed up from Ceres’ deep interior.
“It’s probably material or salt carried in water that evaporated; leaving the white material behind, but we don’t see ice or water on the surface,” Christopher Russell, a UCLA planetary scientist and NASA’s Dawn mission principle investigator, told me.
Yet just from the presence of the spots alone, we infer that Ceres is an active body, says Russell.
“It’s bringing stuff on the surface often enough that we have extremely bright areas that are not dirtied by time as they would be if they were very, very old,” said Russell.
As NASA noted earlier this month, Ceres also likely contains ammoniated clays, which suggests that it may have formed in the vicinity of Neptune and migrated inward to its present location in the Main Asteroid Belt between Mars and Jupiter.
Russell says the dwarf planet could be warmer inside just because of compressive heating, but also because there could be some heat trapped from its formation some 4.56 billion years ago. Or even older than Earth. And at some 584 miles in diameter, Russell says Ceres is big enough that there could be some primordial heat remaining in the center.
NASA reports that some troughs and grooves also appear to be tectonic, reflecting internal stresses that broke Ceres’ crust.
As for looking for life on Ceres?
“The first priority is to look for surface deposits where there’s an active geyser or conduit of material to the surface where those salts are forming,” said Russell, “and then analyze them for biological material.”
The hope is to find microfossils, if not extant life itself, says Russell.
Radar measurements of Ceres’ surface, indicate a clay-like material rather than solid rock. Clay-like material comes with the presence of water, says Russell, so the material on Ceres’ surface was probably wet at one time and then dried out.
As I noted in my book “Distant Wanderers,” one hypothesis about life’s origin on Earth is that at least one of the nucleic acids on which our biological structure is so dependent “emerged from ocean sediments containing sulfur-rich clay compounds called thioesters.”
So, if ribonucleic acid (RNA) formed in a moist clay-like environment on Earth, might some similar nucleic building block have done the same on Ceres?
Dawn data analysis already indicates that Ceres might still host a liquid subsurface layer.
It’s conceivable that if we mounted a follow-on mission to Ceres in the next five to ten years, it’s possible to find evidence of microbial life on Ceres before Mars, says Russell.
It would also be easier to use a surface hopper instead of a rover on Ceres, because the dwarf planet’s gravity is as much as ten times less than that of Mars, says Russell. So, in theory, he says, the engineering needed for such a surface hopper would be ten times easier.
As for extant life on Ceres?
The fact that we’re seeing a lot of brine suggests maybe not, says Russell, but on the other hand people who study extremophile microorganisms find life in extreme environments on Earth.
“It is possible that Ceres has [extant life], but we don’t have any evidence of that yet,” said Russell. “We need to land and dig for it.”