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NASA’s Europa Clipper spacecraft, designed to study Jupiter’s icy moon, could soon be brushed by a stream of charged particles ripped from a comet that didn’t originate in our solar system. The potential encounter, predicted to occur between October 30 and November 6, offers scientists a once-in-a-lifetime opportunity to sample material from an interstellar comet, 3I/ATLAS, without having to chase it.
Researchers Samuel Grant from the Finnish Meteorological Institute and Geraint Jones of the European Space Agency (ESA), who made the prediction, describe the event as both safe and scientifically priceless, Space.com reported.
“We have virtually no data on the interior of interstellar comets and the star systems that formed them,” Grant told Space.com. “Sampling the tail in this way is the closest we can currently get to a direct sample of such an object, and thus a different part of the galaxy.”
At the heart of this cosmic alignment is the comet’s ion tail – a thin, glowing stream of charged particles that always points away from the sun. While no spacecraft is near enough to fly through 3I/ATLAS’s dust tail, Europa Clipper may find itself in the path of the comet’s ion tail, a possibility made clear by the pair’s computer model, Tailcatcher.
“We study cometary bodies because they act as time capsules, sealing in material from their formation billions of years ago,” said Grant. “This material is ejected on approach to the sun, a portion of which is transported away by the solar wind to form the ion tail.”
Using Tailcatcher, Grant and Jones calculated that packets of solar wind — streams of charged particles flowing out from the sun — could carry ions torn from the comet’s tail straight toward Europa Clipper, which is currently orbiting roughly 300 million km from the sun after a recent flyby of Mars. If that happens, the spacecraft’s instruments, built to study Jupiter’s fierce magnetic field, could also detect ions from a different solar system altogether.
The chance encounter depends on several variables: the direction and strength of the solar wind, and the activity level of 3I/ATLAS, which peaks around October 29, when the comet reaches its closest point to the sun, about 200 million km away. As it nears the sun, the comet’s activity is expected to intensify, increasing the volume of material streaming from its surface and widening its ion tail.
“Cometary ions can be distinguished in a number of ways, most simply by chemical abundances. Cometary ions include significant amounts of heavier species, particularly water-group ions, compared to the proton and helium-dominated solar wind,” Grant explained. “Additionally, the act of loading additional mass into the solar wind causes a general slowing and deflection of the ambient solar wind flow.”
ESA’s Hera spacecraft, en route to the asteroid system Didymos and Dimorphos, will also cross the same region between October 25 and November 1. However, Hera lacks the instruments needed to detect charged particles — leaving Europa Clipper as the only spacecraft capable of measuring the interaction directly.
Interestingly, neither Grant nor Jones are part of the Europa Clipper team, meaning the decision to conduct such measurements rests entirely with NASA scientists. Still, Tailcatcher has a solid record: in 2020, it successfully predicted when ESA’s Solar Orbiter would detect ions from comet C/2019 Y4 (ATLAS).
Even if Europa Clipper misses this time, the prediction marks another milestone in scientists’ growing ability to track cometary tail crossings across vast cosmic distances. Looking ahead, ESA’s upcoming Comet Interceptor mission — set to launch in 2029 — aims to directly fly through the coma and tail of a pristine comet, possibly one from another star system.
(With inputs from Space.com)
