Astronomers using the powerful ALMA telescope in Chile have spotted molecular activity in comet C/2014 UN271 (Bernardinelli-Bernstein)—a frozen giant nearly 85 miles wide, making it the biggest active comet ever observed from the distant Oort Cloud.
What’s even more amazing? This icy traveler was more than 16 times farther from the Sun than Earth when it started to show signs of life. ALMA detected dramatic jets of carbon monoxide gas blasting from the comet’s core, like steam escaping from a cosmic kettle.
This is the first time scientists have directly seen what fuels a comet’s activity so far from the Sun, offering exciting clues about how these ancient space visitors behave in the dark, frigid reaches of our solar system.
Even from the frozen edge of our solar system, comet C/2014 UN271 had a story to tell—and the ALMA telescope was listening.
Using its extraordinary sensitivity, ALMA picked up the faint glow of carbon monoxide gas and thermal energy drifting from the comet’s atmosphere, like heat rising from an ember in deep space. Though still incredibly far from the Sun, this giant comet revealed enough of a signal for astronomers to take a closer look.
By combining these new observations with earlier ALMA data from 2022, scientists refined their measurements of UN271’s massive icy core and the dust cloud shrouding it. The result? A sharper, more complete portrait of the largest known Oort Cloud comet—one that’s beginning to whisper secrets from a time before Earth was born.
Thanks to ALMA’s powerful precision, scientists have now confirmed that comet C/2014 UN271 holds the title of the largest Oort Cloud comet ever discovered. By matching its nucleus size and dust mass with previous data, they’ve painted the clearest picture yet of this colossal cosmic traveler.
But the excitement doesn’t stop at size. This discovery marks the first-ever detection of molecular outgassing from this icy giant—a breakthrough that lets us peer into the frozen heart of an object born in the solar system’s infancy. As the comet inches closer to the Sun, scientists expect more hidden gases to awaken and escape, like ancient whispers from the past.
With each puff of vapor, C/2014 UN271 is telling a story—about how Earth may have received its water, and how the building blocks for life might exist elsewhere among the stars. This isn’t just a comet on a journey; it’s a time capsule unraveling the secrets of our cosmic roots.
Journal Reference:
- Nathan X. Roth, Stefanie N. Milam et al. The First Detection of Molecular Activity in the Largest Known Oort Cloud Comet: ALMA Imaging of C/2014 UN271 (Bernardinelli–Bernstein) at 16.6 au from the Sun. The Astrophysical Journal Letters. DOI 10.3847/2041-8213/add526
