Astronomers from New Zealand's University of Canterbury have captured the first evidence of a faint coma around the colossal comet C/2014 UN271 (Bernardinelli-Bernstein), as it edges into the inner solar system. This could be the largest comet ever observed.
Discovered in Dark Energy Survey images from 2014 to 2018, the mega-comet Bernardinelli-Bernstein is now showing initial signs of activity from the Sun's heat.
On June 23, the team used a Las Cumbres Observatory (LCO) telescope in South Africa to image the coma—a glowing halo of gas and dust from sublimating ices in its nucleus. "In our first image, the comet had been obscured by passing satellites, but the others were quite clear. It was there, definitely a beautiful little fuzzy point that contrasted with the sharpness of the neighboring stars," explains lead researcher Michele Bannister from the University of Canterbury.
These early signs appeared when the comet was approximately 19 astronomical units (AU) from the Sun—about twice Saturn's distance, where 1 AU equals roughly 150 million kilometers (Earth-Sun average).
Estimates indicate the Bernardinelli-Bernstein nucleus exceeds 100 km in diameter, roughly three times larger than Comet Hale-Bopp's (seen in 1998) and potentially the most massive comet on record—a thousand times heavier than typical comets.
Hailing from the distant Oort Cloud beyond the Kuiper Belt (5,000–100,000 AU from the Sun), it orbits every 612,190 years. Perihelion arrives in 2031 at less than 10.9 AU, nearing Saturn's orbit.
Though too distant for binoculars from Earth, ground- and space-based telescopes, plus any nearby probes, will study its composition and origins in detail.
