Interstellar comet 3I/ATLAS spews water like a cosmic fire hydrant

Comet 3I/Atlas continues be full of surprises. In addition to being the third interstellar object ever detected, a new analysis shows that it produces emissions of hydroxyl (OH), these compounds betraying the presence of water on its surface. The discovery was made by a team of researchers from Auburn University in Alabama using NASA’s Neil Gehrels Swift Observatory and was described in a study published in The Astrophysical Journal Letters.

Hydroxyl compounds are detectable via the ultraviolet signature they produce. But on Earth, many UV wavelengths are blocked by the atmosphere, so researchers had to use the Neil Gehrels Swift Observatory, a space telescope free of the interference experienced by terrestrial observatories.

Water is present in virtually every comet observed in the solar system, so much so that the chemical and physical reactions of water are used to measure, catalog, and track these celestial objects and their response to heat from the sun. Finding it on 3I/ATLAS means being able to study its characteristics on the same scale as used for regular comets, and this information could in the future be useful data for also studying the processes of comets from other star systems.

“When we detect water – or even its faint ultraviolet, OH, echo – from an interstellar comet, we are reading a note from another planetary system,” Dennis Bodewits, an Auburn University physicist who collaborated on the research, said in a press release. “This tells us that the ingredients of the chemistry of life are not unique to ours.”

Comets are frozen chunks of rock, gas, and dust that typically orbit stars (except for the three interstellar objects found so far). When they are far from a star, they are completely frozen, but as they get closer, solar radiation heats and sublimes their frozen elements, transforming them from solid to gas, some of this material being emitted from the comet’s nucleus thanks to the energy of the star, forming a “tail”.

But with 3I/ATLAS, the data collected revealed an unexpected detail: OH production by the comet was already occurring far from the sun – even though the comet was more than three times further from the sun than Earth – in a region of the solar system where temperatures are normally not high enough to easily produce ice sublimation. However, already at this distance, 3I/ATLAS was releasing water at a rate of about 40 kilograms per second, a rate comparable, the study authors explain, to that of a “maximum fire hydrant.”

This detail seems to indicate a more complex structure than that usually observed in comets in the solar system. This could, for example, be explained by the presence of small fragments of ice detaching from the nucleus of the comet, and which are then vaporized by the heat of the sun, to then feed a gaseous cloud which surrounds the star. This is something that has so far only been observed on a small number of extremely distant comets, and could provide valuable insight into the processes behind 3I/ATLAS.

“So far, every interstellar comet has been a surprise,” Zexi Xing, a researcher at Auburn University and co-author of the discovery, said in a press release. “‘Oumuamua was dry, Borisov was high in carbon monoxide, and now ATLAS is dropping water at a distance where we didn’t expect it. Each is rewriting what we thought we knew about how planets and comets form around stars.”

This story was originally published on CABLE Italy and was translated from Italian.