3 Aug 2025
Comets are an enduring mystery that has confronted astronomers for decades—these so-called dirty snowballs sometimes erupt with activity or even explode at vast distances from our Sun.
Comet activity has been observed two-billion miles from the Sun—where the average temperature in space is a few hundred degrees fahrenheit below zero. Such is the case with comet C/2017 K2 which was found in archival data to have developed a coma while between Uranus and Neptune in 2013. In 2017, NASA's Pan-STARRS1 observed this comet's activity one-billion and a half miles from the sun.
Using the Alma telescope we observe activity in comet C/2014 UN271 as it was inside the orbit of Uranus around 1.5 billion miles away. The comet is legitimately enormous at about 80 miles across, and is described as a pristine Oort Cloud object. The Oort Cloud is a hypothetical—although never observed—shell of icy bodies in the farthest reaches of our solar system.
Independent researcher Stuart Talbott concludes with a prediction for the ESA's upcoming 2029 mission, Comet Interceptor, which will analyze a "pristine ancient comet" in unprecedented detail. Instead, similar every other comet nucleus we've explored, it will appear as another chunk of planetary material electrically blasted into space—because that's exactly what it just might be.
See also:
Largest ever comet discovered near Neptune
What We Know About Interstellar Comet 3I/ATLAS
Symbols of an Alien Sky, Episode 3: The Electric Comet [feature length video]