Observing a comet in the inner Solar System is pretty tough. In the outer Solar System it's nigh-on impossible. So the thought of seeing one beyond, elsewhere in the galaxy, seems rather unlikely.

But that’s exactly what scientists have proposed is possible. The team – from Northern Arizona University, the Carnegie Institution of Washington and the California Institute of Technology – detailed its research in a paper published in the journal Icarus.

It noted how, during the impact of comet Shoemaker-Levy 9 on Jupiter in 1994, a noticeable flash of light was produced. "After the impact, sunlight that would have normally been absorbed by the large amount of methane in Jupiter’s atmosphere was instead reflected by the cometary material from the impacts," the study explained. "As a result… where the planet would normally have low reflectivity, it brightened substantially and stayed brighter for at least a month."

Using the same technique, the team says it could be possible to see a giant exoplanet suddenly get brighter when a comet strikes it. While existing telescopes are not sufficient to observe such an event, future telescopes like the James Webb Space Telescope (JWST), due to launch in 2018, could do the job. "The good thing is that the required technology is only one step above our current observational capabilities," Ricardo Hueso of the University of the Basque Country in Bilbao, Spain, who was not involved in the study, told New Scientist.

The method would require looking at a distant planet at near-infrared wavelengths, and it would also have to be a gas giant like Jupiter or bigger in size to be noticeable. Nonetheless, it’s thought that the impact would be visible for about a month. Young solar systems that are full of debris would be good candidates to look for such impacts.

And aside from just being pretty interesting, such observations have a scientific value, too. Observing cometary impacts in young systems, and finding out how often they occur, could have implications for our own Solar System. It’s thought that a comet or an asteroid may have been responsible for transporting water, and even life, to Earth early in its history. Seeing impacts in a young system could suggest such an event was plausible.