We’re about to find many more interstellar interlopers: here’s how to visit one

A long-period comet is an icy visitor from the far reaches of the solar system that has spent a short time getting blasted by the Sun’s heat and radiation, freezing its physical and chemical properties as they were billions of years ago.

Long-period comets are typically discovered a year or two before approaching the Sun, which still does not leave enough time to develop a mission from scratch. With Comet Interceptor, the ESA will launch a probe to loiter in space a million miles from Earth, wait for the right comet to arrive, then fire its engines to pursue it.

There is a good chance that the right comet will come from the solar system. “That’s the goal of the mission,” Snodgrass told Ars.

But if astronomers detect an interstellar object coming toward us on the right trajectory, there’s a chance Comet Interceptor could reach it.

“I think the whole science team would agree, if we get really lucky and there’s an interstellar object we could hit, then to hell with the normal plan, let’s go for it,” Snodgrass said. “It’s an opportunity you can’t leave there.”

But, he added, it is “very unlikely” that an interstellar object would be in the right place at the right time. “Even though everyone is still very excited about the possibility, and we are excited about the possibility, we’re trying to kind of keep the expectations at a realistic level.”

For example, if Comet Interceptor were in space today, there is no way it could reach 3I/ATLAS. “It’s unfortunate,” Snodgrass said. “Its closest point to the Sun, it reaches the point on the other side of the Sun from Earth. Just bad timing.” If an interceptor were parked elsewhere in the solar system, it might be able to move into position for an encounter with 3I/ATLAS. “There is only a limited amount of fuel on board,” Snodgrass said. “There’s only so far we can go.”