Interstellar Comet 3I/ATLAS Offers Unexpected Science Opportunity for Hera and Europa Clipper
A fleeting chance to study an interstellar comet’s tail has emerged, with two spacecraft – Hera and Europa Clipper – potentially able to gather data as they pass near the object in the coming weeks. A new study suggests leveraging these missions, originally designed for asteroid and Jovian moon exploration, to analyze the ions streaming from comet 3I/ATLAS, the third interstellar object ever discovered.
Scientists have long been captivated by interstellar objects, offering a rare glimpse into the composition of planetary systems beyond our own. While some suggestions regarding 3I/ATLAS have veered into the realm of speculation, including theories of alien spacecraft, a recent paper accepted for publication by the Research Notes of the American Astronomical Society proposes a pragmatic approach. Researchers Samuel Grand of the Finnish Meteorological Institute and Geraint Jones of ESA detail a plan to utilize the fortuitous positioning of two existing missions.
Both Hera and Europa Clipper are currently en route to vastly different destinations within our solar system. Hera is headed to the Didymos-Dimorphos binary asteroid system, the site of NASA’s successful DART mission in 2022. Europa Clipper, as its name suggests, is bound for Europa, one of Jupiter’s four Galilean moons, with a mission to investigate its potential for harboring life beneath its icy shell.
However, a remarkable coincidence has presented itself. According to the study, both spacecraft are projected to pass “downwind” of 3I/ATLAS within the next two weeks. Hera will be within range for observations between October 25th and November 1st, while Europa Clipper has a slightly longer window, from October 30th to November 6th.
“A few weeks isn’t a whole lot of time to set up a rapid experiment to run a test that neither spacecraft were designed for,” the study acknowledges. Despite the short timeframe and the fact that neither mission was specifically equipped for comet tail analysis, scientists believe this represents the best opportunity to study the interstellar visitor’s tail.
The comet’s tail has been steadily growing since its discovery in early June, with recent observations indicating a significant release of water. This activity is creating a substantial wake of water particles and, crucially, ions. While 3I/ATLAS is no longer visible from Earth-based telescopes, its tail is expected to continue expanding as it approaches perihelion – its closest approach to the Sun – on October 29th.
Analyzing the tail’s composition isn’t as simple as flying directly behind the comet. The solar wind, a stream of charged particles emanating from the Sun, pushes these particles outward, creating a curved path. The speed of the solar wind significantly influences the tail’s shape and location, dictating where a spacecraft would need to pass to collect meaningful data.
To estimate the optimal trajectory, the researchers employed a model called “Tailcatcher”, which predicts the path of cometary ions based on varying solar wind speeds. This model calculated the “minimum miss distance” for each spacecraft relative to the comet’s tail. Even with these calculations, the spacecraft are expected to pass millions of kilometers from the tail’s central axis – approximately 8.2 million km for Hera and 8 million km for Europa Clipper. However, the vast scale of cometary tails, particularly those of active comets like 3I/ATLAS, means that detectable ions can spread over immense distances.
A key challenge lies in the instrumentation onboard each spacecraft. While Europa Clipper is equipped with a plasma instrument and magnetometer capable of directly detecting ions and magnetic field changes within the tail, Hera lacks the necessary tools for such measurements. “At least one of the spacecraft – Hera – doesn’t have any instruments that could potentially detect either the ions expected in the tail, nor the magnetic ‘draping structure’ that characterizes what the comet’s atmosphere does to the magnetic field carried by the solar wind,” the study notes.
The feasibility of this impromptu experiment hinges on swift action. Mission controllers for both Hera and Europa Clipper must assess the potential opportunity and, if deemed viable, adjust their spacecraft’s operations within a very limited timeframe. The possibility of directly sampling an interstellar comet’s tail – a feat never before accomplished – is a compelling incentive. As one researcher stated, “it would be something to brag about that had nothing to do with their original intended mission.”
The original version of this article was published on Universe Today.
