We Need to Intercept Our Next Interstellar Visitor to See If It's Artificial, Astronomers Say in New Study

Scientists are gaming out the best way to intercept objects that zoom into our solar system from interstellar space, an effort that could provide close-up views of entities that hail from alien star systems. Sending spacecraft to catch up with these interstellar objects, and potentially capture images of them from distances of just a few hundred miles, could reveal important details about their composition, evolution, and their origin beyond our solar neighborhood, reports a new study.

It’s been only five years since the discovery of the first known interstellar visitor—a mysterious 300-foot-wide object known as ‘Oumuamua—which was spotted traveling through the solar system in October 2017. In addition to its sheer novelty, ‘Oumuamua was something of an oddball that puzzled scientists, especially because it underwent a sudden speed boost that still remains unexplained. 

Scientists have presented many natural possible origins for the object, while the Harvard astronomer Avi Loeb has famously suggested that it may have been a piece of alien technology. If an intercept mission had been ready to chase down ‘Oumuamua five years ago, we might have some answers to the tantalizing question of the object’s nature and origin. To ensure we don’t miss our next shot at rendezvousing with a similarly strange object, scientists hope to develop a spacecraft that can lay in wait until it is given the green light to pursue an interstellar target.

Now, a team led by Amir Siraj, a student pursuing astrophysics at Harvard University, have outlined some of the physical parameters of such a mission, including the potential timeline, spacecraft speed, and optimal distance of a flyby. 

Whereas past studies have mapped out the feasibility of the concept, Siraj and his co-authors, including Loeb, investigated the “requirements for a rendezvous mission with the primary objective of producing a resolved image of an interstellar object” and discuss “the characterization from close range of interstellar objects that, like ‘Oumuamua, don’t have an unequivocally identified nature,” according to a forthcoming study in the Journal of Astronomical Instrumentation that was posted on Sunday to the preprint server arXiv.

“We thought that how we could be most helpful to the conversation is by laying out the physical considerations that go into planning an interceptor mission,” Siraj said in a call with Motherboard. “What are the limits, set by physics, you can't get around no matter what?”

“This can be a useful resource for any other team that is putting together specific designs for interstellar object missions,” he continued. “This is basically the physics checklist that the mission needs to satisfy, and this also contextualizes the type of mission that we would need to successfully do this.”

Siraj and Loeb have published many studies about interstellar objects, and have identified two meteors that hit Earth over the past decade that may have been interstellar in origin. The pair are now working on an expedition to try to recover the remains of one of the meteors, which struck in 2014, from the South Pacific seafloor. 

Loeb thinks that it’s possible that both ‘Oumuamua and the 2014 meteor could be artificial in origin, which has provoked pushback from many other scientists who have said there is insufficient evidence for this position. An intercept mission to an interstellar body could shed light on this question, which is why Siraj and his colleagues discuss ways to distinguish between artificial and natural objects. 

“We may anticipate that the spectra of artificial materials of extrasolar provenance may exhibit marked differences with respect to both naturally occurring and human-manufactured materials,” the researchers said in the new study. 

“If the main objective of the mission is to discriminate a possible artificial interstellar probe from a natural asteroid or cometary object,” then using a spectrometer “sensitive to the wavelength range of 0.4 to 2.5 µm may be sufficient, based on reference spectra of various artificial and natural minerals,” they added.

The new study also notes that the Vera C. Rubin Telescope’s Legacy Survey of Space and Time (LSST), a huge 10-year astronomical survey, will be an excellent detector for interstellar objects, and could potentially spot dozens of these visitors. An intercept mission would need to rapidly select one of these potentially abundant targets after its detection, then blast off within weeks in order to have enough time to catch up with it.

“If you're going to go after an interstellar object with a billion dollar spacecraft, you probably want it to look a little bit unusual,” Siraj said. “For an ‘Oumuamua-sized object, it's a couple of months for the trip and for an object 10 times dimmer than ‘Oumuamua, meaning a third of the size of ‘Oumuamua, the trip would be a couple of weeks, so you would need to really decide very quickly.”

For this reason, Siraj and his colleagues suggest parking a spacecraft in Lagrange Point 2 (L2), a stable region in space where the James Webb Space Telescope is currently located. From this spot, a spacecraft could swiftly chase after objects that appear interesting at first glance, though the team noted that a mission could also be parked in orbit around Earth or the Moon, or could launch from the ground. 

The mission would then conduct a flyby of the object, ideally from a distance of several hundred miles, which would reveal invaluable insights about its size, shape, composition, and potential origin. 

The European Space Agency is already developing a Comet Interceptor that will lurk in L2 and might end up pursuing an interstellar object, though the mission is more geared toward rendezvousing with a pristine comet from the outer regions of the solar system. A team of NASA scientists has also presented a “Bridge to the Stars” mission that aims to intercept an interstellar object, but this project remains in the concept phase for now.  

If an official interstellar intercept mission is eventually greenlit in the coming years, it would offer an unprecedented glimpse of an object from beyond the solar system. Meanwhile, the catalog of known interstellar objects will only expand as the LSST and other next-generation observatories scan the skies for these interlopers. Such surveys may reveal whether ‘Oumuamua was really an outlier, or if there are many objects like it wandering through interstellar space. 

“It's remarkable to me that there still isn’t an explanation that doesn't invoke a new type of astrophysical object for ‘Oumuamua,” Siraj said. “That's very motivating for me and, I think, for a lot of scientists.”