Comet Bernardinelli–Bernstein
What is Comet Bernardinelli–Bernstein?
Comets· Nucleus ~140 km — largest known. The comet with the largest nucleus known, about 140 km across and more than ten times the size of Halley's. It will come in as far as Saturn's orbit in 2031 before heading back out.
Orbit and period
| Nucleus | ~140 km — largest comet known |
|---|---|
| Perihelion | Jan 2031, 10.9 AU near Saturn's orbit |
| Period | millions of years — ≈3.0 million inbound, ≈5.1 million outbound |
| Found at | 29 AU (imaged 2014, identified 2021) |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Why Bernardinelli–Bernstein woke up so far out
Comets usually become active only as they near the Sun. Sunlight turns ice into gas, the gas lifts dust, and the dust forms a hazy cloud around the nucleus called a coma. Yet this comet already had a coma in September 2018, when it was 23.8 AU from the Sun. The coma was found by going back through images taken by NASA's TESS satellite.
That far out it is colder than −200 °C, too cold for water ice to turn into gas. Scientists therefore think the activity is driven by ices such as carbon monoxide, which become gas at much lower temperatures. In September 2021 the coma was also seen to brighten suddenly in an outburst, which is estimated to have released 10 to 100 million kg of dust.
Even at its closest the comet comes in only as far as Saturn. Its water ice never evaporates in earnest, so it keeps ancient ice that has barely been touched by the Sun's heat. That makes it a valuable sample of the material the solar system was built from, and the months around its 2031 perihelion will be the best time to study it.
The comet in depth
Comet Bernardinelli–Bernstein was identified in June 2021 by Pedro Bernardinelli and Gary Bernstein, who were searching through images from the Dark Energy Survey (DES). Because of that, the earliest discovery image dates from 2014. The comet was then 29 AU from the Sun, meaning 29 times the Earth–Sun distance, which is about as far out as Neptune.
What makes the comet famous is its size. A comet's solid body, the nucleus, is a lump of ice and dust. This one is about 140 km across, roughly the distance from London to Birmingham. That is more than ten times the size of Halley's nucleus and nearly twice that of Comet Hale–Bopp, the previous record-holder.
The comet comes from the Oort cloud, the reservoir of icy bodies at the far edge of the solar system. About 1.5 million years ago it passed its farthest point, some 42,000 AU from the Sun, and it has been falling inward ever since. Its closest approach comes in January 2031, but even then it will be 10.9 AU from the Sun, near Saturn's orbit. It will never be visible to the naked eye, only through large telescopes.
Follow the comet in the orbit view and its path is extremely long and narrow. Most well-known comets swing in close to Earth, but this one turns around near Saturn and heads back out. After it leaves, millions of years will pass before it returns.
Frequently asked
- How close does Comet Bernardinelli–Bernstein get to the Sun?
- The perihelion of Comet Bernardinelli–Bernstein is Jan 2031, 10.9 AU near Saturn's orbit.
- How long is the orbital period of Comet Bernardinelli–Bernstein?
- The period of Comet Bernardinelli–Bernstein is millions of years — ≈3.0 million inbound, ≈5.1 million outbound.
- In one line, what is Comet Bernardinelli–Bernstein?
- Comets — The comet with the largest nucleus known, about 140 km across and more than ten times the size of Halley's.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.