He thought TESS's longer exposure times could provide more detail.įarnham and his colleagues combined thousands of images of comet BB collected by TESS from 2018 through 2020. When Farnham heard about the discovery, he immediately wondered if images of comet BB had been captured by the Transient Exoplanet Survey Satellite (TESS), which observes one area of the sky for 28 days at a time. Most comets are around 1 km or so and much closer to the sun when they are discovered. The survey captured the bright nucleus of the comet but did not have high-enough resolution to reveal the envelope of dust and vapor that forms when the comet becomes active.Īt 100 km across, comet BB is the largest comet ever discovered by far, and it is farther from the sun than the planet Uranus. Scientists first discovered comet BB in June 2021 using data from the Dark Energy Survey, a collaborative, international effort to survey the sky over the Southern hemisphere. How warm it must be to start vaporizing depends on what kind of ice it contains (e.g., water, carbon dioxide, carbon monoxide or some other frozen compound). As an orbiting comet approaches its closest point to the sun, it warms, and the ices begin to vaporize.

Often called 'dirty snowballs' or 'icy dirtballs,' comets are conglomerations of dust and ice left over from the formation of the solar system. Knowing when a comet becomes active is key to understanding what it's made of. 'These observations are pushing the distances for active comets dramatically farther than we have previously known,' said Tony Farnham, a research scientist in the UMD Department of Astronomy and the lead author of the study. The finding was published in The Planetary Science Journal on November 29, 2021. The finding will help astronomers determine what BB is made of and provide insight into conditions during the formation of our solar system.

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