Comet 3I/ATLAS from beyond the solar system carries a key molecule for life

The interstellar comet 3I/ATLAS releases carbon-rich chemicals at a higher rate than almost all other comets in our solar system. One of these compounds is methanol, a key ingredient in prebiotic chemistry that has not been observed in other interstellar objects.

3I/ATLAS, only the third visitor to our solar system from another part of the galaxy, appears to be unlike any comet in our own galactic neighborhood. As it moved toward the sun, an envelope of water vapor and gas quickly developed around it, which also contained much larger amounts of carbon dioxide than seen in typical comets in the solar system. The comet’s light also appeared much redder than usual, indicating possible unusual surface chemistry, and it began releasing its gases while relatively far from the sun, an indication that it may not have passed near another star in hundreds of millions of years, or since it left its home star system.

Now, Martin Cordiner of NASA’s Goddard Space Flight Center in Maryland and colleagues used the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to discover that 3I/ATLAS produces significant amounts of hydrogen cyanide gas, and even larger amounts of methanol gas. “Molecules like hydrogen cyanide and methanol are present in trace amounts and are not the dominant constituents of our own comets,” says Cordiner. “Here we see that actually, in this alien comet, they are very abundant.”

Cordiner and his team found that hydrogen cyanide gas originated relatively close to the comet’s rocky core and was produced in quantities of about a quarter to half a kilogram per second. Methanol has also been found in the core, but it also appears to be produced in significant quantities in the comet’s coma, which is the long tail of dust and gas located several kilometers from the comet itself.

Methanol appeared in much larger quantities than hydrogen cyanide – about 40 kilograms per second – and made up about 8% of the total vapor coming from the comet, compared to about 2% for standard comets in the solar system. The differences in the location of these two molecules also suggest that the comet’s nucleus is not uniform, which could potentially tell us something about how it formed, Cordiner says.

Although methanol is a relatively simple carbon compound, it provides a key stepping stone toward the production of more complex molecules essential for life, Cordiner explains, and would likely be produced in large quantities when other chemical reactions producing these molecules occur. “It seems chemically implausible that one could go down the path of very high chemical complexity without producing methanol,” says Cordiner.

Josep Trigo-Rodríguez, of Spain’s Institute of Space Sciences, and his colleagues predicted that a comet rich in metals like iron should also produce relatively large amounts of methanol, because liquid water, released by the sun’s heat, would begin to pass through the comet’s core and react chemically with its iron compounds – a process that should create methanol. As such, finding traces of methanol in the comet’s coma could be a sign that the comet is relatively rich in metals, he says.