Two Probes Will Dive into the Tail of an Interstellar Comet express
Stretched for millions of kilometers, the tail of Comet 3I/ATLAS consists of rarefied gas and microscopic dust grains. In late October 2025, two Earth probes, Europa Clipper and Hera, will plunge into it. Neither was designed to encounter a comet: Clipper is headed for a moon of Jupiter, Hera for an asteroid. But their trajectories accidentally intersected the tail.
Onboard instruments will capture particles of dust and hydrogen, and measure how the stream of charged particles from the Sun changes.
Composition analysis will tell us whether other worlds resemble ours. It’s like dipping a sample from an unfamiliar ocean. These data will turn hazy guesses about other planetary systems into measurable chemistry.
Original abstract
as written by the authors arXiv:2510.13222
During October - November 2025, interstellar comet 3I/ATLAS, will pass upstream of the Europa Clipper and Hera spacecraft. Here, we identify two potential opportunities for in-situ observations of 3I's ion tail by immersion, facilitated by the close alignment between the comet's hyperbolic trajectory with the ecliptic plane. During the period 30 October - 6 November 2025, it is predicted that Europa Clipper will potentially be immersed within the ion tail of 3I/ATLAS, providing the opportunity to detect the signatures of an interstellar comet's ion tail. Characteristic changes to the solar wind are also expected to be observed; a magnetic draping structure associated with the comet may be identifiable. It is further predicted that spacecraft Hera will possibly be immersed within the ion tail of 3I/ATLAS during the period 25 October - 1 November 2025.
Comet 3I/ATLAS was discovered in 2025—it’s only the fourth interstellar object ever spotted by humans, after the asteroid ‘Oumuamua.