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 farthest reaches of the solar system that has spent little time exposed to the sun's heat and radiation, freezing its physical and chemical properties in the same way they were billions of years ago.

Long-period comets are usually discovered a year or two before approaching the Sun, but there is still not enough time to develop a mission from scratch. WITH Comet InterceptorESA will launch a probe that will sit in space a million miles from Earth, wait for the desired comet to appear, and then fire its engines to chase it.

There is a high probability that exactly that comet will come from the solar system. “That’s the essence of the mission,” Snodgrass told Ars.

But if astronomers detect an interstellar object approaching us on the right trajectory, there is a chance that an interceptor comet could reach it.

“I think the whole science team would agree: If we get really lucky and there's an interstellar object that we can reach, then to hell with the usual plan, let's go and do it,” Snodgrass said. “This is an opportunity that can’t just be left behind.”

But, he added, it is “very unlikely” that an interstellar object will be in the right place at the right time. “While everyone is always very excited about this opportunity and we're excited about this opportunity, we kind of try to keep expectations at a realistic level.”

For example, if the Comet Interceptor were in space today, there is no way it could reach 3I/ATLAS. “It’s an unfortunate incident,” Snodgrass said. “Its closest point to the Sun, it reaches a point on the other side of the Sun from the Earth. Just bad timing.” If the interceptor were parked somewhere else in the solar system, it could be in position to rendezvous with 3I/ATLAS. “There’s not a lot of fuel on board,” Snodgrass said. “We can only go so fast.”