Comets, with their long, beautiful, bright tails of ice, are some of the most spectacular sightings in the night sky. This was most apparent when Comet NEOWISE passed by Earth in the summer of 2020, dazzling viewers from all over the planet while being mainly visible in the northern hemisphere. Even though the sky might look the same night after night, comets are a humble reminder that the universe is a very active and beautiful place.

This ground-based image of comet C/2020 F3 (NEOWISE) was taken from the Northern Hemisphere on July 16, 2020. The inset image, taken by the Hubble Space Telescope on Aug. 8, 2020, reveals a close-up of the comet after its pass by the Sun. Hubble’s image zeroes in on the comet’s nucleus, which is too small to be seen. It’s estimated to measure no more than 3 miles (4.8 kilometers) across. Instead, the image shows a portion of the comet’s coma, the fuzzy glow, which measures about 11,000 miles (18,000 kilometers) across in this image. Comet NEOWISE won’t pass through the inner solar system for another nearly 7,000 years. (Credits: NASA, ESA, STScI, Q. Zhang (Caltech); ground-based image copyright © 2020 by Zoltan G. Levay, used with permission)

Comets are remnants of a time long past, and by long past we mean a very long past, as they are frozen leftovers from the formation of the solar system. While we are fortunate to see them as dazzling spectacles, they don’t start off this way. Comets are snowballs of frozen gases, rock, and dust orbiting in the edge of the solar system known as the Kuiper Belt where it is hypothesized that billions of comets likely exist. Every so often, one of their orbits brings it close to the Sun where it heats up and spews all that frozen dust and gas into a tail that stretches away from the Sun for millions of miles.

Kuiper Belt and Oort Cloud in context. (Credit: European Space Agency)

But what about comets that come from outside the solar system? Are they also frozen leftovers from the formation of another solar system like our own? These questions only became greater when our solar system was visited by ‘Oumuamua in 2017, which was the first known interstellar object to visit our solar system. While only visible from Earth for 11 days before it exited our solar system, scientists were able to determine that it was much longer that it was wide, possibly by a factor of five to ten. While this cigar-shaped planetary body is possibly gone forever, questions remain about its origin and composition. But what if were able to visit other interstellar comets that pay a visit to our neck of the galactic woods?

Artist’s concept of interstellar object1I/2017 U1 (‘Oumuamua) as it passed
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