3I/ATLAS: Interstellar comet has water unlike any in our solar system
3I/ATLAS is quite strange
International Gemini Observatory/NOIRLab/NSF/AURA/B. Bolin
Interstellar comet 3I/ATLAS contains water and carbon molecules at levels never before seen in our solar system. This suggests that it formed around a radically different alien star that was much older than the sun.
Astronomers have been tracking 3I/ATLAS since it entered our solar system last year – and it’s weird. It appears to contain far more carbon dioxide and water than almost any other comet we’ve seen, and early estimates put its age at 8 billion years, almost twice that of the sun.
Now, Martin Cordiner of NASA’s Goddard Space Flight Center in Maryland and his colleagues have discovered that its levels of deuterium – a form of hydrogen with an extra neutron – are at least 10 times higher than in any comet we’ve seen before.
Deuterium exists naturally in small amounts in Earth’s oceans, but levels in 3I/ATLAS are more than 40 times higher. “3I/ATLAS continues to amaze us with what it reveals about the similarities and differences of its host system from our own solar system,” says Cordiner. He and the team used the James Webb Space Telescope to make the observations.
“This is truly exceptional,” says Paul Hartogh of the Max Planck Institute for Solar System Research in Germany. “This deuterium/hydrogen ratio in water is extremely unusual, and no one would have expected it.”
Such high levels of deuterium are usually only seen in the colder regions of the Milky Way, says Ewine van Dishoeck of the Leiden Observatory in the Netherlands. “This means that it is probably in the outermost part of the disk, around the star it was rotating around, which also makes it easier to expel,” says Dishoeck.
Cordiner and his colleagues also discovered relatively low levels of carbon-13 – a form of carbon with an extra neutron that is typically produced after stars explode in a supernova. Low levels of carbon-13, which have also been found in young star-forming clouds, suggest that 3I/ATLAS formed at a time in the galaxy’s history when there were not as many polluting supernovae. This suggests that the comet must have formed around a star system about 10 to 12 billion years old, more than twice as old as the sun, Cordiner says.
However, Dishoeck says the precision we have on carbon levels means we can’t be certain of its age.
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