The recent discovery of the third known interstellar object (ISO), 3I/ATLAS, has brought about another round of debate on whether these objects could potentially be technological in origin. Everything from random YouTube channels to tenured Harvard professors have thoughts about whether ISOs might actually be spaceships, but the general consensus of the scientific community is that they aren’t. Overturning that consensus would require a lot of “extraordinary evidence”, and a new paper led by James Davenport at the DiRAC Institute at the University of Washington lays out some of the ways that astronomers could collect that evidence for either the current ISO or any new ones we might find.

That evidence, known in the search for extraterrestrial intelligence (SETI) circles as “technosignatures”, implies that a technological civilization crafted the objects making their way through our solar system. Technosignature searches don’t just happen for ISOs though – there are branches of SETI that look at everything from Dyson swarms around other stars to trying to find a hidden Monolith like that from 2001: A Space Odyssey somewhere on a moon in our solar system.

Since ISOs are still a relatively new discovery, despite their theorized existence for years, they are at the forefront of technosignature research. And the paper posits four different types of technosignatures astronomers might be able to find on one of them.

Fraser discusses how we might find ISOs.

The first one might seem obvious, but it’s caused a lot of controversy over the last few years. If an ISO moves quickly in a way that can’t be explained by gravity, then it’s likely due to some sort of thruster, and hence a technosignature. The key word in that sentence is quickly as there are other forces that could move an ISO more slowly, such as outgassing or radiation pressure. Even something as slight as changing its rotation instead of its trajectory could be a sign that an ISO is being controlled. The first discovered ISO, `Oumuamua, exhibited some non-gravitational acceleration, which caused quite a stir in the astronomical community, but it was most likely caused by a combination of the other two non-gravitational forces, despite the number of catastrophizing YouTube videos made about it at the time.

A second technosignature on an ISO would be unnatural spectra. Because aliens would definitely paint their interstellar starship, right? But more realistically, they might coat it with some kind of enhanced material, or even have something as mundane as a viewport that would show up in a different spectra than what we would expect to see on a natural object. Since there would likely be at least computers on board, it might also emit a higher infrared (i.e. heat) signature than would be expected, which would also be visible to some of our telescopes. So far all three ISOs have exhibited only standard, natural spectra, with nothing overtly strange about them.

Third would be a strange shape. Most designs for our own interstellar ships at this point require a giant solar sail – so a thin sheet or similar design would be a good indication that the object wasn’t natural. However, detecting the shape of an object is difficult directly. It can be inferred by the object’s rotation, though again that rotation can be influenced by processes such as outgassing and radiation pressure.

Fraser discusses a project that could potentially catch up to an ISO to take close-up data for the first time.

The final technosignature would be one of SETI’s longest-standing practices – a transmission. SIgnals coming from a relatively close-by object could be much weaker than even those coming from the closest stars and we would still be able to detect them. They could come in the form of radio transmissions, or lasers, but either way, a detection of those kinds of signals coming from an object would serve as pretty iron-clad proof that it was technological in origin.

One advantage of the techniques proposed in this paper is that all of the data needed to prove them would already be collected by telescopes doing other science to a relatively unique object. There’s no required observational times or special equipment needed. Though special equipment could help, as various plans have been proposed for a mission to visit future ISOs in a Rendezvous with Rama scenario, though any such mission has yet to receive funding.

The future looks bright for ISO research, though, with the upcoming Vera Rubin Observatory expected to find upwards of 50 new ISOs in the coming decades. As we get more experience monitoring these interstellar visitors, we’ll learn more of what they typically look like, and that will eventually make us more capable of noticing when something truly is “off” about one of them. It might only be a matter of time before we finally do get confirmation that we’re not alone.

Learn More:

J. R. A. Davenport et al – Technosignature Searches of Interstellar Objects

UT – TESS Spotted 3I/ATLAS Two Months Before It Was Discovered – It Was Even Active Then

UT – Tracking the Interstellar Objects 1I/’Oumuamua, 2I/Borisov, and 3I/Atlas to their Source

UT – Could We Launch a Mission to Chase Down Interstellar Comet 3I/ATLAS?