Organic molecules have been spotted on the dwarf planet Ceres. The discovery was made by the Dawn mission, which has previously found evidence of water ice at the planet's poles and carbonate minerals, that appear to be responsible for the mysterious bright spots on the surface. Taken together, astronomers say that Ceres now has the ingredients and favorable conditions for life.
Including things like carbohydrates, nucleic acids and proteins, organic molecules are the basic building blocks of life. Earth is obviously crawling with them, but they have also been found in meteorites and on Mars. Evidence suggests that these compounds could form out in space, before finding their way to planets where favorable conditions allow them to assemble into living organisms.
"What we've found on Ceres is probably the most unambiguous detection of organics on any Solar System body other than Earth," says Carlé Pieters, co-investigator on the Dawn mission. "We've collected meteorites on Earth with organic signatures, which makes us think their parent asteroids may have had organics. But until now we haven't seen such definitive evidence on any asteroid. So this could help us put together the history of organics in the Solar System."
The Dawn orbiter made the discovery using a spectrometer to map the surface in visible and infrared wavelengths. By measuring which wavelengths bounce back and which ones are absorbed, the instrument can compare those readings with the signatures of known materials and determine the composition of the surface.
"There's a highly diagnostic absorption feature for organics at a wavelength of 3.4 microns, and we saw that signal very clearly on Ceres," says Pieters. "But it's not everywhere. It's very localized across a particular region."
The region in question is called Ernutet, a crater-ridden area in the dwarf planet's north. Deposits of organic molecules were found scattered across a space of about 400 square miles (1,036 sq km), close together in some parts and more spread out in others. While the researchers can't be sure where the minerals may have come from, previous studies suggest that hydrothermal processes below the surface could have bubbled them up from underground, in the same way that the carbonate deposits formed. An alternate hypothesis holds that a cloud of debris could have rained them down to the surface from space.
"There are high-resolution data available from Dawn that provide the geologic context for these deposits," says Pieters. "We're looking at those data now, which will help us to pin down the origin of these materials."
While it's a far cry from confirming life on Ceres, the presence of organic molecules is a major box to tick off the checklist. Already crossed off that list are things like sub-surface water ice, abundant clay minerals, ammoniated minerals and evidence of hydrothermal activity. All together, these conditions paint a portrait of a place with "favorable environments for prebiotic chemistry," and future investigations may help determine if life ever has, or still could, exist on the dwarf planet.
"It's kind of like baking a cake," explains Pieters. "You can have all the ingredients, but if you don't put them together properly, you don't end up with a cake. So there is still plenty of work to be done before we can start thinking about whether microbes were able to form on Ceres."
The research was published in the journal Science.