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

Interstellar comet 3I/ATLAS releases carbon-rich chemicals at a faster rate than almost any other comet in our solar system. One such compound is methanol, a key ingredient prebiotic chemistry this has not been observed in other interstellar objects.

3I/ATLASwhich is only the third visitor to our solar system from elsewhere in the galaxy, appears to be completely unlike any comet from our galactic neighbors. As it moved toward the Sun, a shell of water vapor and gas quickly grew around it, which also contained much larger amounts of carbon dioxide than we see in typical comets in the Solar System. The comet's light also appeared much redder than normal, indicating a possible unusual surface chemistry, and it began releasing its gases while relatively far from the Sun, indicating that it may not have passed close to another star in hundreds of millions of years or since it left its home star system.

Now, Martin Cordiner at 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 produced significant quantities of hydrogen cyanide gas and even larger quantities of methanol gas. “Molecules such as hydrogen cyanide and methanol are present in trace amounts and are not the dominant components of our own comets,” says Cordiner. “Here we see that there are a lot of them on this alien comet.”

Cordiner and his team found that hydrogen cyanide was emanating relatively close to the comet's rocky nucleus and was produced in quantities ranging from a quarter to half a kilogram per second. Methanol was also found in the comet's nucleus, but it also appears to have been produced in significant quantities in the comet's coma, which is a long tail of dust and gas many kilometers away from the comet itself.

Methanol appeared in much larger quantities than hydrogen cyanide—about 40 kilograms per second—and made up about 8 percent of the total vapor coming from the comet, compared with about 2 percent for standard Solar System comets. The differences in the arrangement of the two molecules also suggest that the comet's nucleus is heterogeneous, which could ultimately tell us about how it formed, Cordiner says.

Although methanol is a relatively simple carbon-containing compound, it is a key step toward producing the more complex molecules needed for life, Cordiner says, and is likely to be produced in large quantities when other chemical reactions that produce those molecules occur. “It seems chemically incredible that you could go down a path of very high chemical complexity without producing methanol,” says Cordiner.

Trigo-Rodriguez Joseph from the Institute of Space Sciences in Spain and his colleagues predicted that a comet with a high content of metals such as iron should also produce relatively large amounts of methanol, because liquid water released by the sun's heat would begin to push through the comet's nucleus and react chemically with its iron compounds, a process that should create methanol. So finding traces of methanol in a comet's coma could be a sign that the comet is relatively rich in metals, he says.