Astrobiologists like to think that forming solar systems result in cauldrons of plenty; cornucopias of molecular compounds that make for terrestrial worlds just itching to form life. But observations of an eroding debris disk around the nearby red dwarf star AU Microscopii (AU Mic) hint that young planets orbiting such M-stars may be bone dry and lifeless.
The observations — described this past week at the American Astronomical Society’s (AAS) Winter meeting here in Seattle, detail the first-ever images of a debris disk around a young red dwarf star. Observing with NASA’s Hubble Space Telescope and the European Southern Observatory’s Very Large Telescope (VLT) in Chile, the young, 23 million-year-old star lies only 32 light-years away in the southern constellation of Microscopium.
“If AU Mic is representative, it implies that little will remain in the disk at the time when planets in the habitable zone have cooled sufficiently to retain volatiles,” an international team, led by John Wisniewski at the University of Oklahoma in Norman, writes. The team notes that AU Mic’s disk is expected to be completely eroded in another million and a half years.
Why does this matter?
Some seventy percent of all stars tend to be low-mass red dwarfs. If even half are producing planets that are likely to be astrobiologically-stillborn, that cuts the odds for any sort of extrasolar life dramatically.
The standard paradigm for Earth’s own formation is that it formed dry with a hot molten surface. But over hundreds of millions of years, it accreted water and other necessary molecular building blocks that originated from asteroids and comets in our early outer solar system.
To date, only about 40 stars have been observed to harbor starlight-scattering debris disks which reveal the presence of such small particles, Glenn Schneider, a team co-investigator and an astronomer at the University of Arizona’s Steward Observatory, told me. “This is not because they are conceived as rare, but rather that they are observationally challenging and we likely are seeing only the tip of [the] iceberg,” he said.
The team reported via the Space Telescope Science Institute that it had spotted at least six dusty blobs with diameters large enough to stretch from our Sun to our own Jupiter, on the southeast side of AU Mic’s disk. They are traveling at speeds of between 9,000 and 27,000 mph; fast enough to escape the star’s gravitational clutches, the institute notes.
These blobs appear to be ejecting particles from the disk, which likely started out with an outer rim of small icy bodies, not unlike our own early solar system’s Kuiper Belt. If this disk hadn’t been eroded away, the team says it might have provided ices to seed its dry inner planets.
The physical mechanism responsible for expelling blobs of material from AU Mic’s disk is still an open question , Wisniewski told me. One idea is that powerful coronal mass ejections are providing the force to expel disk material. And the hope is that ongoing observations will characterize how often AU Mic exhibits massive flares that could lead to disk material being expelled.
But Wisniewski says that if AU Mic is representative of typical young red dwarf systems, then the vast majority of terrestrial planets that form in their habitable zones might indeed be lifeless.
“Our work provides another example that the formation and early evolution of our own solar system might not be representative of other planetary systems,” said Wisniewski.
I’m a science journalist and author of “Distant Wanderers: the Search for Planets Beyond the Solar System” who writes about over-the-horizon technology, primarily astronomy and space science. I’m a former Hong Kong bureau chief for Aviation Week & Space Technology maga (Read More)