All sorts of crazy things were proposed regarding 3I/ATLASthe third known interstellar object we have discovered. Some are simply conspiracy theories about it being an alien spacecraft, while others are well-thought-out proposals, such as using Mars probes to observe a comet streaking past the Red Planet.
New paper pre-published on arXiv and accepted for publication in the Research Notes of the American Astronomical Society by Samuel Grand and Geraint Jones of the Finnish Meteorological Institute and ESA accordingly, falls into the latter category and proposes using two spacecraft already en route to their destinations to potentially detect ions from the object's spectacular tail that formed as it approached. Sun.
A few weeks is not a lot of time to organize a quick experiment and conduct a test that no spacecraft was designed for. But sometimes science means doing the best you can with what you've got, and in this case, these two spacecraft are the best choice for studying the tail of an interstellar comet.
This tail has been growing steadily since the comet's discovery in early June. Recent reports of water gushing out of it show how massive the tail has become, leaving behind a trail of water particles, but more importantly, ions. The comet also recently disappeared from view of Earth systems, although its tail is expected to continue to grow until it reaches perihelion on October 29.
As the article explains, being in part of its tail is not as simple as passing directly behind it as it moves through the solar system: the solar wind pushes particles further away from the Sun, following a curved path away from the comet. The speed at which the wind hits these particles plays an important role in where they will end up, and therefore where exactly the spacecraft will have to go to directly collect tail data.
To make these estimates, the authors used a model called “Tailcatcher,” which estimates where cometary ions will travel based on different wind speeds. He then calculated the “minimum miss distance” for a given spacecraft along the central axis of the comet's tail. Unfortunately, the model's accuracy is no better than solar wind data, which is typically collected only after the fact—and certainly not in enough time to help achieve this potential mission goal.
Even with the program's best estimates, the two spacecraft would be millions of kilometers away from the central axis—about 8.2 million for Hera and 8 million for Europa Clipper. However, this is still within the scope of collecting ion data directly from the tail, as they can extend millions of kilometers from very active comets such as 3I/ATLAS.
The downside to this plan is that at least one of the spacecraft, Hera, does not have any instruments that could potentially detect either the ions expected in the tail or the magnetic “draping structure” that characterizes what a comet's atmosphere does to the comet's body. magnetic field carried by the solar wind. However, Europa Clipper does – its plasma instrument and magnetometer are exactly what will be needed to directly detect these ions and changes in the magnetic field.
Acting on this serendipity is challenging to say the least, but it is also very time-constrained. It is unclear whether controllers of the Hera mission, or more importantly the Europa Clipper, will see the message in time to do anything about their potential journey through a coma. But if they do, they could become the first in human history to directly sample the tail of an interstellar comet – and wouldn't that be a bragging point that has nothing to do with their originally intended mission?
original version this article was published on Universe today.
