For the first time, scientists have identified rich, complex organic molecules on the dwarf planet Ceres — the kind of carbon-based compounds that are the building blocks for primitive life. The discovery could catapult Ceres to near the top of the list of places targeted in the search for extraterrestrial life.
The molecules are called aliphatic organic compounds, and by all indications they formed on Ceres itself, rather than arriving via an external source like an impacted comet. Fans of the panspermia hypothesis — the theory that life throughout the universe has been “seeded” by traveling asteroids and comets — might look to this new data for support, but they won’t find it here. Ceres features enough water and possible heat-retention of its own to explain the evolution of the newfound molecules. It’s also pretty isolated compared to many other asteroids in our solar system (it’s classified as a small planet, but it’s more like an asteroid in terms of how it’s situated - the largest object in the belt that stretches between Mars and Jupiter). A paper describing the findings was published Thursday in the journal Science.
“We prefer the hypothesis of formation in Ceres itself,” says first author Maria Cristina De Sanctis. “It would be difficult to deliver material between Ceres and other bodies, not just organic material but [as a] general problem.”
De Sanctis and her colleagues made the observations using the Visible and InfraRed Mapping Spectrometer — a feature of NASA’s Dawn spacecraft, which studies Ceres alongside the asteroid Vesta and the surrounding objects in the belt. Ceres was the first dwarf planet ever visited by a spacecraft, when Dawn entered its orbit in 2015.
What they saw was that on Ceres’s surface near the crater Ernutet (in the tradition of naming celestial objects after ancient gods and goddesses, this was the Egyptian goddess of fertility), there were signs of the right groups of methyl and methylene to support the presence of aliphatic compounds. If you’re picturing brackish primordial ooze, you’re not far off — the minerals are described as “tar-like.” Another reason the science indicates these compounds were formed on Ceres and not elsewhere is that these particular molecules likely wouldn’t have survived the extreme heat of an impact event. Nor does their pattern of distribution across Ceres’s surface fit with an impact theory.
“Overall, I think it’s possible to transfer organic material from one body to another, or to bring by comet,” says Michael Kueppers, the author of a related paper on Ceres’s complex molecules. “But Ceres is the largest object around [that area], and also I associate panspermia more with the movement of microbes through the solar system and universe … this is about organic material.”
De Sanctis agrees, noting that while it’s possible to get a mix of impacted material and target material, that’s not the main hypothesis in this case. Her research didn’t reveal any evidence for small asteroid, pieces of debris, or other spatial material of any kind around Ceres.
“For other asteroids, for Vesta, we have a very large family [number of surrounding objects] that could also reach the Earth, but not for Ceres,” De Sanctis says.
Both scientists believe that Ceres will now gain much greater traction as an object on which to theoretically find microbial life. It could even compete with Mars as the most prominent candidate. It’s already a more attractive target than the two other big names that tend to come up in this discussion — Europa and Enceladus — because a) it’s closer to Earth and therefore easier to potentially investigate and b) the radiation in its environment is more benign. Plus, in addition to having the right chemistry to make an appealing biological study, it’s the proper distance from the sun for sustaining ice — not too close or too far, but just right.
When we’re differentiating between organic molecules that might indicate life and the ones that are just molecules, the factor most important to bear in mind is temperature, explains NASA planetary protection officer Catharine Conley. Ceres is extremely cold, so it would take something else - discovery of a liquid core, say - to get us really hoping for alien life.
It’s important to contextualize the discovery not just in relation to Mars and various distant moons, but in relation to everything out there we haven’t had the chance to study yet. Organic compounds are all over the place — pretty much everywhere you have oxygen and carbon and hydrogen, which are the among the most common molecules in the universe. We will find organic compounds in many more places just as soon as we have the means to look there, and only a fraction of those, if any, will actually translate to biological life. The carbon chemistry required to create life the way we think of it on Earth is really, really complex, and the conditions needed to approximate it are narrow.
But being able to understand what reactions are taking place on Ceres helps us understand exactly what those boundary conditions are. And as we go forward with these studies, it’ll be more vital than ever that we do so in controlled, sanitized settings — we’ll never be able to make any headway on the panspermia hypothesis if there’s a chance that non-indigenous life we find was introduced by our own scientific meddlings.
“We know there’s life on Mars,” says Conley. “It’s Earth life, and we put it there.”
We don’t actually know whether life, in the universe as a whole, is easy or hard to form, because we only have our own example — n=1, in science-speak — Earth. At least, for the time being.
In the meantime, at least we still have this:
The delivery of extraterrestrial complex organic molecules to Earth may have been important for the origin and early evolution of life (1) and signatures of organic matter on solar system bodies have been sought for decades. Organic compounds, including amino acids, occur in some chondritic meteorites, possibly formed during aqueous alteration on their parent bodies (2,3,4) and/or as the result of interstellar photochemistry (5). However, organics have not been unambiguously identified on the surfaces of asteroids (meteorite parent bodies) or on outer solar system objects, with few exceptions (6-12). Here we report the clear detection on dwarf planet Ceres of an absorption at 3.4 μm that is characteristic of the presence of organic matter. The existence on Ceres of a mixture of ammonia-bearing hydrated minerals, water ice, salts (13-16), and organic material indicates a complex chemical environment that could allow the formation of prebiotic molecules.