Comet Bernardinelli–Bernstein
What is Comet Bernardinelli–Bernstein?
Comets· Nucleus ~140 km — largest known. The largest comet nucleus ever measured — about 140 km, more than ten times Halley's. It has fallen from the Oort cloud for three million years and will skim Saturn's orbit in 2031 before heading back. Invisible to the naked eye, but its vast orbit is worth a look in the orbit view.
The orbit of Comet Bernardinelli–Bernstein at this moment: https://nowsky.org/solar/orbit?fw=bb&sp=80 — replayed live, no login.
Orbit and period
| Nucleus | ~140 km — largest comet known |
|---|---|
| Perihelion | Jan 2031, 10.9 AU near Saturn's orbit |
| Period | ~4 million years (round trip to the Oort cloud) |
| Found at | 29 AU (imaged 2014, identified 2021) |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Frequently asked
- How close does Comet Bernardinelli–Bernstein get to the Sun?
- Jan 2031, 10.9 AU near Saturn's orbit.
- How long is the orbital period of Comet Bernardinelli–Bernstein?
- ~4 million years (round trip to the Oort cloud).
- In one line, what is Comet Bernardinelli–Bernstein?
- Comets — The largest comet nucleus ever measured — about 140 km, more than ten times Halley's.
A comet already awake beyond 20 AU
When Bernardinelli–Bernstein was confirmed in 2021 it was 20 AU from the Sun — the distance of Uranus — and already wrapped in a coma. Water ice does not sublimate that far out; far more volatile ices such as carbon monoxide were evaporating in sunlight at −200 °C and lifting dust, making it one of the most distant comets ever seen active. Re-examining the 2014 Dark Energy Survey images revealed a faint coma even at 29 AU.
At its January 2031 perihelion the comet comes in only as far as Saturn's orbit (10.9 AU), so its water ice never sublimates in earnest. It will never be a naked-eye object, but scientifically it is a chance to observe Oort-cloud ice almost untouched by the Sun's heat. The 140 km diameter of the nucleus was measured in 2022 by Hubble, which separated the light of the nucleus from that of the coma.
The comet in depth
Comet Bernardinelli–Bernstein (C/2014 UN271) was identified in June 2021 by Pedro Bernardinelli and Gary Bernstein while mining Dark Energy Survey data; the earliest images dated from 2014, when it was 29 AU from the Sun. Hubble observations in 2022 pinned the nucleus at about 140 km across — more than twice the previous record-holder, Hale–Bopp, and the largest comet ever measured.
It left the Oort cloud roughly three million years ago and is now falling toward the inner solar system; its aphelion lies some 40,000 AU away. Even at discovery, beyond the orbit of Uranus, it was already active with a coma, driven by ices such as carbon monoxide that sublimate at extreme cold. Its January 2031 perihelion at 10.9 AU, near Saturn's orbit, keeps it far too faint for the naked eye, but large telescopes will follow it for years.
Track the comet in the orbit view and you will notice it never enters the inner solar system like other comets — it turns around near Saturn and heads back out. Proposals for a spacecraft encounter are already on the table.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.