Two spacecraft, Hera and Europa Clipper, are set to traverse the tail of comet 3I/ATLAS in the coming weeks. A recent study by Samuel Grand and Geraint Jones, affiliated with the Finnish Meteorological Institute and the European Space Agency, respectively, proposes that these missions could be leveraged to analyze the tail”s ions as the comet approaches the Sun.
Since its discovery in early June, 3I/ATLAS has generated various theories and suggestions, ranging from conspiracy notions about alien spacecraft to practical scientific proposals. Hera is currently en route to the Didymos-Dimorphos binary asteroid, which was impacted by the DART mission in 2022, while Europa Clipper is on a mission to study the icy surface of Europa, one of Jupiter”s Galilean moons.
Both spacecraft are fortuitously positioned to pass “downwind” of 3I/ATLAS within a short time frame. Hera”s pass is scheduled between October 25 and November 1, while Europa Clipper will follow from October 30 to November 6. Although the timeframe is tight for setting up an experiment, the scientific community is eager to utilize these spacecraft for an unexpected opportunity to gather data on the comet”s tail.
The tail of 3I/ATLAS has been expanding, with recent reports highlighting significant water release, indicating a substantial presence of water particles and potentially ions. Despite the comet”s recent move out of view from Earth-based telescopes, it is expected that its tail will continue to grow until it reaches perihelion on October 29.
However, tracking ions in the tail is not straightforward. The solar wind influences the trajectory of particles emitted from the comet, causing them to follow a curved path away from the Sun. To navigate these complexities, the researchers employed a model called “Tailcatcher,” which predicts the paths of cometary ions based on varying solar wind speeds. Using this model, they were able to estimate the “minimum miss distance” for both spacecraft relative to the comet”s tail.
Despite the best estimates, the spacecraft will likely be millions of kilometers from the tail”s central axis—approximately 8.2 million kilometers for Hera and 8 million kilometers for Europa Clipper. Nonetheless, this distance is still within a range that might allow for the detection of ions, as they can disperse significantly from active comets like 3I/ATLAS.
A limitation of this plan is that Hera lacks the necessary instruments to detect the expected ions or the magnetic structures indicative of the comet”s interaction with the solar wind. In contrast, Europa Clipper is equipped with a plasma instrument and a magnetometer that would enable it to measure these ions and associated magnetic field variations.
As mission controllers for both spacecraft evaluate this unexpected opportunity, time is of the essence. If they manage to seize this chance, they may become the first to collect samples from the tail of an interstellar comet, an achievement that would represent a significant milestone in space exploration.
