Largest comet ever observed revealed to be older than first thought

Bernardinelli-Bernstein (BB) is the largest comet ever observed, and a new study from the University of Maryland shows it may have been active a lot longer than previously thought.

Comets are conglomerations of ice and dust left over from the formation of a solar system, and as one approaches a star, it will warm and begin to vaporize. A comet is active when the ice vaporizes, creating an envelope of dust and vapor around it known as the coma. The ice within the comet could be frozen water, carbon dioxide, carbon monoxide, or several other compounds, all requiring different conditions to vaporize.

BB is massive, at 100 kilometers across, and exists in our solar system further from the Sun than Uranus. Using the Transient Exoplanet Survey Satellite (TESS) to examine previous observations of BB, researchers determined from its distance from the Sun and its size, BB's coma is made primarily from carbon monoxide. Carbon monoxide can begin to vaporize up to five times farther from the Sun than where BB was first observed, suggesting BB has been active for significantly longer.

"We make the assumption that comet BB was probably active even further out, but we just didn't see it before this. What we don't know yet is if there's some cutoff point where we can start to see these things in cold storage before they become active," said Tony Farnham, a research scientist in the UMD Department of Astronomy and the lead author of the study.

"This is just the beginning. TESS is observing things that haven't been discovered yet, and this is kind of a test case of what we will be able to find. We have the potential of doing this a lot, once a comet is seen, going back through time in the images and finding them while they are at farther distances from the Sun."

You can read more from the study here.