spaceSpace and PhysicsspaceAstronomy

How To Catch An Interstellar Comet

A team of astronomers have outlined what is necessary if we are to send a spacecraft to study a future interstellar visitor to our solar system.


Stephen Luntz

Stephen has a science degree with a major in physics, an arts degree with majors in English Literature and History and Philosophy of Science and a Graduate Diploma in Science Communication.

Freelance Writer

An artist's impression of Rosetta visiting Comet 67P/Churyumov-Gerasimenko. Soon we might be able to do this with an interstellar visitor
An artist's impression of Rosetta visiting Comet 67P/Churyumov-Gerasimenko. Soon we might be able to do this with an interstellar visitor. Image credit: ESA/ATG Medialab

In 2017 and 2019 the detections of the only two objects known to have passed through our Solar System from outside marked an extraordinary leap for science. However, the information we could glean from each of them was frustratingly basic. Astronomers have started planning so that when such events happen again, we can transform our knowledge of the universe beyond the sphere warmed by the Sun’s glow by sending spacecraft to photograph them at close range.

When ‘Oumuamua was spotted, fans of classic science fiction immediately saw parallels with the plot of Rendezvous with Rama, a novel in which a spacecraft and crew are diverted to investigate a visiting alien spaceship on a similar path. If the proposed film comes to fruition, it may even have the comet to thank. However, the book was set a century in the future, when humans have a base on Mars and much greater capacity to intercept incoming objects than we have today. 


A preprint of a paper on, yet to be peer reviewed, considers the likelihood of another interstellar visitor over the next ten years. It then looks at how we could investigate it, albeit by uncrewed spacecraft rather than a plucky band of astronauts. 

The work is a long way from being implemented by NASA or other space agencies. If the idea is approved, any final version will probably look very different, but the work may start a more rigorous conversation on how one of the most exciting missions of the near future could occur.

The authors anticipate us spotting 15 visitors over a decade, but with only a sample of two to extrapolate from the error bars are wide – from just 0.38 up to 84. 

The first requirement for a mission to catch one of these would be to get plenty of warning. With a host of new telescopes either recently online or about to arrive, that condition may soon be met. 


Then, we would need a spacecraft ready to go. Rather than contend with the delays any launch from Earth risks, such as those due to bad weather, the authors propose getting it into space before we have a target. The craft would then be stowed at a Lagrange point – they suggest L2 where the JWST is based – and activated when the need arises.

Of course, just catching one visitor at close range will not be enough to quench astronomers’ thirst for knowledge. Little though we know, we are sure ‘Oumuamua and its successor, 2I/Borisov, are very different beasts, with the latter apparently resembling a comet from the outer reaches of our own system and ‘Oumuamua unlike anything seen before. Even a sample from one, let alone close-range photography, would have told scientists nothing about the other. Images taken within 1,000 kilometers (621 miles) of an intruder, as the authors suggest, would likely spark a quest for more.

One remaining question is whether such a craft should go after the first possible target, which might be an apparently boring object, or if it should wait in the hope of something more interesting.

The preprint’s second author is Harvard's Professor Avi Loeb, who severely damaged his reputation by pushing the idea ‘Oumuamua was an alien spacecraft to the popular media. Although it makes a divergence to discuss this idea, the preprint also covers more mainstream theories of ‘Oumuamua’s origins, and its conclusions regarding future missions don’t rely on the theory.


The preprint can be found at 


spaceSpace and PhysicsspaceAstronomy
  • tag
  • comet,

  • Astronomy,

  • interstellar objects,

  • Comet Borisov,

  • Intersellar comet,

  • ‘Oumuamua,

  • Rendevous with Rama