The science of interstellar objects is moving swiftly. Now that we have the third ‘interloper’ into our Solar System (3I/ATLAS), we can consider how many more such visitors we’re going to find with new instruments like the Vera Rubin Observatory, with its full-sky images from Cerro Pachón in Chile. As many as 10,000 interstellar objects may pass inside Neptune’s orbit in any given year, according to information from the Southwest Research Institute (SwRI).
The Gemini South Observatory, likewise at Cerro Pachón, has used its Gemini Multi-Object Spectrograph (GMOS) to produce new images of 3I/ATLAS. The image below was captured during a public outreach session organized by the National Science Foundation’s NOIRLab and the Shadow the Scientists initiative that seeks to connect citizen scientists with high-end observatories.
Image: Astronomers and students working together through a unique educational initiative have obtained a striking new image of the growing tail of interstellar Comet 3I/ATLAS. The observations reveal a prominent tail and glowing coma from this celestial visitor, while also providing new scientific measurements of its colors and composition. Credit: Gemini Observatory/NSF NOIRlab.
Immediately obvious is the growing size of the coma, the cloud of dust and gas enveloping the nucleus as 3I/ATLAS moves closer to the Sun and continues to warm. Analyzing spectroscopic data will allow scientists to understand more about the object’s chemistry. So far we’re seeing cometary dust and ice not dissimilar to comets in our own system. We won’t have this object long, as its orbit is hyperbolic, taking it inside the orbit of Mars and then off again into interstellar space. Perihelion should occur at the end of October. It’s interesting to consider, as Marshall Eubanks and colleagues do in a new paper, whether we already have spacecraft that can learn something further about this particular visitor.
Note this from the paper (citation below):
Terrestrial observations from Earth will be difficult or impossible roughly from early October through the first week of November, 2025… [T]he observational burden during this period will, to the extent that they can observe, largely fall on the Psyche and Juice spacecraft and the armada of spacecraft on and orbiting Mars. Our recommendation is that attempts should be made to acquire imagery from encounter spacecraft during the entire period of the passage of 3I through the inner solar system, and in particular from the period in October and November of 2025, when observations from Earth and the space telescopes will be limited by 3I’s passage behind the Sun from those vantage points.
As we consider future interstellar encounters, flybys begin to look possible. Such was the conclusion of an internal research study performed at SwRI, which examined costs and design possibilities for a mission that may become a proposal to NASA. SwRI was working with software that could create a large number of simulated interstellar objects, while at the same time calculating a trajectory from Earth to each. Matthew Freeman is project manager for the study. It turns out that the new visitor is itself within the study’s purview:
“The trajectory of 3I/ATLAS is within the interceptable range of the mission we designed, and the scientific observations made during such a flyby would be groundbreaking. The proposed mission would be a high-speed, head-on flyby that would collect a large amount of valuable data and could also serve as a model for future missions to other ISCs [interstellar comets].”
Image: Upper left panel: Comet 3I/ATLAS as observed soon after its discovery. Upper right panel: Halley’s comet’s solid body as viewed up close by ESA’s Giotto spacecraft. Lower panel: The path of comet 3I/Atlas relative to the planets Mercury through Saturn and the SwRI mission interceptor study trajectory if the mission were to be launched this year. The red arc in the bottom panel is the mission trajectory from Earth to interstellar comet 3I/ATLAS. Courtesy of NASA/ESA/UCLA/MPS.
So we’re beginning to undertake the study of actual objects from other stellar systems, and considering the ways that probes on fast flyby missions could reach them. 3I/ATLAS thus makes the case for further studies of flyby missions. SwRI’s Mark Tapley, an expert in orbital mechanics, is optimistic indeed:
“The very encouraging thing about the appearance of 3I/ATLAS is that it further strengthens the case that our study for an ISC mission made. We demonstrated that it doesn’t take anything harder than the technologies and launch performance like missions that NASA has already flown to encounter these interstellar comets.”
The paper on a fast flyby mission to an interstellar object is Eubanks et al., “3I/ATLAS (C/2025 N1): Direct Spacecraft Exploration of a Possible Relic of Planetary Formation at “Cosmic Noon,” available as a preprint.
The fact this thing exists and is here suggests that interstellar space is not nearly as empty as we think it is. Could that interstellar space being full of objects be the real reason why high speed (> 10% light speed) interstellar travel is impossible?
Interstellar space is largely empty. Even the inside of the solar system in the densest part of the asteroid belt is largely empty. The distance between two km-sized asteroids is millions of km. This distance is even larger outside of the asteroid belt, and even much larger in interstellar space. Such “big” objects are really not the big problem — the probability of encountering any by chance is virtually zero. You can note that whatever spacecraft exploring the solar system never approaches very close to any asteroid by random chance — either it’s a planned close approach, or it’s at best a very distant approach (millions of km at best).
What can be much more critical for near-c travels is actually tiny dust grains — of course they are much smaller, but globally much more numerous, so the probably of encountering any is much larger. And if you go a near-c speed, even a tiny dust grain can have a large energy that can produce critical damages.
In the forseeable future, not any inhabited extrasolar mission is realistically imaginable (even going to Mars is not done yet), but sending uninhabited nanospacecrafts (gramme-scale objects) is something that is being worked about at the scale of the century. We may not see the launch of such interstellar nanospacecrafts during our lifetime, but it may happen within the next few generations. The idea would be to send swarms of redundant nanospacecrafts (maybe hundreds or more nanospacecrafts), with each spacecraft having one instrument (camera etc.) — and therefore, in the whole swarm, there would be multiple times each instrument. Such tiny spacecrafts could be accelerated at a significant fraction of c (the concept imagines 20% of c (~20 years of travel) for a simple flyby of Proxima, and maybe 5% of c (~century-scale travel) if we want the swarm to enter into orbit around Proxima) by using huge lasers. Of course, we are currently far from being able to build such miniaturised spacecrafts, and to build such huge lasers — hence why I said it’s an idea that is being worked about with a realistic aim of launch at the scale of the next century.
A small complement to link the “dust grain” part and “nanospacecarft part” in my first comment: the point of having redundant spacecraft would be exactly to mitigate the risk of losing a number of nanospacecrafts (for whatever reason, it be the spacecraft having a problem, a spacecraft being destroyed by such a tiny dust grain, or whatever else) during travel. The point is that, even if part of the swarm is lost before reaching the target system (e.g. Proxima), we can expect to still have at least one (ideally several) instrument of each type in the end — and therefore being able to study the target system as expected.
Using what vehicle?
Still waiting for that information to be released. So far the study remains internal to SwRI.
We know other interstellar visitors will be coming. We need to prepare intercept missions now. We have no excuses any more.
https://youtu.be/Pke3u-HI3PM?feature=shared
As interstellar visitors start to become old hat, maybe we have something more exotic to get excited about: intergalactic visitors! According to https://aasnova.org/2021/03/23/understanding-the-origin-and-arrival-rates-of-interstellar-objects/ there should be roughly one interstellar object approaching from Milky Way halo stars per 11 years, with velocity >200 km/s.
When we go beyond the galaxy, the models for any potential extraterrestrials change. What if a halo star came from a small, ancient galaxy where every system was colonized, artifacts everywhere, but then civilization somehow died out, billions of years before it merged with the Milky Way? Then any one of these halo-derived objects – only! – might, in theory, be encrusted with alien libraries, homes, and artworks just waiting for the first probe to make it up to 200 km/s to check out an unknown visitor.
I’ll admit that’s a slender scenario, but I don’t see a way to rule it out.
I’d like to get some confirmation on the numbers here:
Visiting interstellar comet 3I/Atlas by current tech: New Horizons model. Part 1.
https://www.linkedin.com/posts/robert-clark-94273688_dawn-moessner-gabe-rogers-stacy-weinstein-weiss-activity-7367915873266847744-81Jd
And:
Visiting interstellar comet 3I/Atlas by current tech: New Horizons model. Part 2.
https://www.linkedin.com/posts/robert-clark-94273688_visiting-interstellar-comet-3iatlas-by-current-activity-7367919978311761920-85wx
Proposes using a Falcon 9 launcher to launch a Centaur upper stage plus 2 smaller solid stages to get a 10 kg minisat to a flyby of 3I/Atlas as it crosses Jupiters orbit in March, 2026.
But what can we hope to learn from these interstellar interlopers?
Granted, they may contain evidence of conditions where they were formed, or of conditions that existed long after their formation, but we still don’t know where they originated, or when, or how long they have been flying around the galaxy being exposed to who knows what conditions.
Yes, we have every reason to believe these objects are extremely common (especially when we now have the technical means of detecting them), but how their current condition or their distribution is related to their origin or to conditions in the galaxy since its formation will remain a mystery until we have collected data on an enormous number of them for a very long time. The minimum first step will be to study how their overall properties are correlated to one another. Just because some may contain more or less ammonia or methane or ice or rock than others will tell us little. Even a detailed inventory of their isotopic abundances will contribute little to our understanding on how they fit into the big picture..
No, I’m NOT suggesting we should ignore them. Any opportunity to examine interstellar objects in detail should be welcomed, and sooner or later we may stumble on some really revealing facts about them. But I suspect that most of them will look pretty much the same, and what differences they do have amongst themselves will be very difficult to fit into any theoretical framework concerning galactic or stellar or planetary evolution we can devise at this time.
I’m hoping we get lucky and find one with purely bizarre characteristics, but I doubt it will play out this way. What I suspect is that the line-up of suspects will play out to be a collection of unique misfits (like our own asteroid belt, or our catalog of planetary satellites) with little clue as to their origin or role in galactic history. Only a very long experience with these objects is likely to result in sufficient data to propose an explanatory theory, and an even longer experience will be required to test that theory.
We’ve always known these guys were out there. We’re just talking about them now because we have the tech to see them.