Science

NASA’s Dawn mission finds life’s building blocks on dwarf planet Ceres


NASA's Dawn mission finds life's building blocks on dwarf planet Ceres

It sure doesn’t pay to underestimate Ceres: NASA’s Dawn spacecraft has spotted signs of organic molecules on the frigid dwarf planet. The findings, published in the journal Science, may shed light on the prevalence of pre-life chemistry in the solar system while marking Ceres as one of the worlds that could potentially host microbial life.

“Because Ceres is a dwarf planet that may still preserve internal heat from its formation period and may even contain a subsurface ocean, this opens the possibility that primitive life could have developed on Ceres itself,” Michael Küppers of the European Space Agency, who was not involved in the study, wrote in a commentary.

“It joins Mars and several satellites of the giant planets in the list of locations in the solar system that may harbor life.” Ceres, one of five dwarf planets in the solar system, is also an asteroid – the largest of them, in fact. Formed around 4.5 billion years ago, it sits in the belt of rocky debris that lies between the orbits of Mars and Jupiter.

Asteroids are the leftover building blocks of planetary formation, largely unchanged by geologic processes that occur in the Earth and other planets – and so studying these space fossils can help scientists piece together what the early solar system looked like.

Among the asteroids, Ceres is special. As a dwarf planet, it got stuck somewhere along the way to becoming a full-grown world. Frozen in this state, Ceres can also offer a snapshot of planetary adolescence.

A region around the Ernutet crater on Ceres is rich in organic compounds. The color coding shows the strength of the organics absorption band, with warmer colors indicating the highest concentrations. (Image Courtesy of NASA/JPL-Caltech/UCLA/ASI/INAF/MPS/DLR/IDA)

A region around the Ernutet crater on Ceres is rich in organic compounds. The color coding shows the strength of the organics absorption band, with warmer colors indicating the highest concentrations. (Image Courtesy of NASA/JPL-Caltech/UCLA/ASI/INAF/MPS/DLR/IDA)

Scientists have long wondered whether asteroids had not just water but also organic matter that could have been brought to Earth – perhaps giving life the right chemical ingredients to emerge. Water and organic molecules have been discovered in meteorites that are thought to be chunks of asteroids that fell to Earth.

But it’s also possible some of that may have simply been contaminated or transformed by Earth’s environment. Hints of organics have been found on two actual asteroids, 24 Themis and 65 Cybele, but the signal was pretty weak. (ESA’s Rosetta mission found clear signals on comet 67P/Churyomov-Gerasimenko – but that, of course, is not an asteroid.)

Thanks to NASA’s Dawn spacecraft, which reached the frigid little world in 2015, scientists have detected super-bright salt deposits in craters as well as an ice volcano named Ahuna Mons. But now, using its Visible and InfraRed Mapping Spectrometer, the spacecraft has picked up organics lying on the surface.

When light hits any material, that material will absorb certain wavelengths while reflecting the rest – and the absorbed wavelengths are unique to the material’s properties. A spectrometer uses those missing bands of light like a chemical fingerprint to identify the composition of the surface.

The detected organic matter lies in a roughly 1,000 square-kilometer area near a roughly 50-kilometer-wide crater named Ernutet. While the scientists aren’t sure exactly what the compounds are, the fingerprint is characteristic of material containing carbon-hydrogen bonds, and may include components like methyl and methylene.

“We were not expecting to see something like this on the surface of Ceres,” said study coauthor Christopher Russell, a UCLA planetary scientist and Dawn’s principal investigator. These simple molecules, he added, are “really pre-biological, but they’re in the family of materials that we would expect if Ceres was working its way along the complexity path.”

Together with some of the other stuff already known to be on Ceres, this makes for what could theoretically be a life-friendly environment, perhaps even an environment with the right chemical precursors for life.

“The combined presence on Ceres of ammonia-bearing hydrated minerals, water ice, carbonates, salts, and organic material indicates a very complex chemical environment, suggesting favorable environments to prebiotic chemistry,” the study authors wrote.

But how did the organics get there? One possibility is that they were delivered by comets or other asteroids – but the organic material’s distribution doesn’t match the pattern left by an impact. Besides, any organic-rich body that slammed into Ceres would probably be superheated by the collision, causing much of that organic matter to break down, the authors pointed out.

If the organics really do originate on Ceres itself, as the authors suspect, then they’ll have to figure out how this material made it from the dwarf planet’s interior to its surface—a process that for now remains a mystery.

Whatever the explanation, the findings show that Ceres – like Mars and other worlds like Enceladus – may also have all the right chemical ingredients for life. Scientists could learn more if they could look at the water ice’s isotopic composition, Russell added.

This could reveal whether Ceres formed where it lies, or whether it formed farther out and eventually moved in. But that, he said, would require a lander of some sort, not remote sensing. Perhaps that’s a job for a future mission to the dwarf planet. Sourcelatimes

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