3I/ATLAS is quite strange
International Gemini Observatory/NOIRLab/NSF/AURA/B. Bolin
The interstellar comet 3I/ATLAS contains water and carbon molecules at levels never before seen in our solar system. This suggests that it formed around an alien star radically different from and 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 be packed with far more carbon dioxide and water than almost any other comet we’ve seen, and early estimates put it at 8 billion years old—almost twice the age of the Sun.
Now Martin Cordiner at NASA’s Goddard Space Flight Center in Maryland and his colleagues have found that the 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 occurs naturally in small amounts in the Earth’s oceans, but the 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 the host system compared to our own solar system,” says Cordiner. He and the team used the James Webb Space Telescope to make the observations.
“It’s truly unprecedented,” says Paul Hartogh of the Max Planck Institute for Solar System Research in Germany. “This deuterium-to-hydrogen ratio in water is extremely unusual and no one would have expected this.”
Such high levels of deuterium are typically only seen in the coldest regions of the Milky Way, says Ewine van Dishoeck at the Leiden Observatory in the Netherlands. “That means it’s probably in the outer part of the disc around whatever star it circled, and that also makes it easier to kick it out,” says Dishoeck.
Cordiner and his colleagues also found relatively low levels of carbon-13 – a form of carbon with an extra neutron that is usually produced after stars explode in a supernova. Low levels of carbon-13, also found in young star-forming clouds, point to 3I/ATLAS forming at a time in the galaxy’s history when there were not as many contaminating supernovae. This suggests that the comet must have formed around a star system around 10 billion to 12 billion years old, more than twice the age of the Sun, says Cordiner.
However, Dishoeck says the precision we have for the carbon levels means we can’t be sure of the age.
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