See that cluster of bright objects in the above image? Those are fragments of a comet called C/2019 Y4 (ATLAS) which broke apart recently, dashing hopes that it would become a bright naked-eye-visible comet. If the comet hadn’t broken up it would have been an amazing sight in the night sky this month. Luckily, Hubble was at the ready to show us a different amazing sight: the fragments just after the break up.
Comets are largely composed of rock held together by ice, so it’s fairly common for them to break apart when they start to get closer to the Sun. Comet ALTAS is a type of comet called a Kreutz sungrazer, which are comets which all come from one original comet that broke apart less than 1,700 years ago. The original comet was probably around 100 km across – absolutely huge for a comet! – and that’s why its pieces have gone on to form a whole family of new comets.
Kreutz sungrazers often fall apart when they get close to the Sun, but they have also produced many spectacular comet displays over the centuries. The above image is of the Great Comet of 1882, which was so bright it could be seen in daylight. We didn’t get to see anything like that with Comet ATLAS, but maybe next time!
Featured image credit: NASA, ESA, STScI and D. Jewitt (UCLA)