Comet Borisov
The first comet known to come from another star, found by an amateur with a telescope he built himself.
Key facts
- Designation
- 2I/Borisov
- Type
- Interstellar comet
- Orbital period
- none: it is on a one-way, hyperbolic path
- Closest to the Sun
- 2.0 AU (about 300 million km), on 8 December 2019
- Farthest from the Sun
- none; it is leaving for good
- Tilt of orbit
- about 44°
- Nucleus
- less than 1 km across
- Discovered
- by Gennady Borisov in Crimea on 30 August 2019
- Returns
- never: it is heading out of the Solar System
Orbit
Borisov entered the Solar System at about 32 km/s relative to the Sun, far too fast to be captured. Its orbit has an eccentricity of about 3.4, where anything above 1 means an open, one-way path. It passed the Sun in December 2019 outside the orbit of Mars and Earth at about 290 million km, and is now leaving.
Size and nature
Unlike 'Oumuamua, Borisov looked like an ordinary comet, with a coma and a tail. Its nucleus is small, under a kilometre across. Its gas was unusually rich in carbon monoxide, more than in almost any comet from our own Solar System, which suggests it formed in a very cold place, far from its own star. In March 2020 it threw off a fragment.
History
Gennady Borisov, an engineer and amateur astronomer, found it from his own observatory in Crimea with a 65 cm telescope he had made. It was spotted on its way in, unlike 'Oumuamua, so it was watched for over a year by telescopes including Hubble.
Why it matters
Borisov showed that comets around other stars are made of much the same things as ours, ice, dust and simple molecules, with differences in the mix. That is strong evidence that the processes that built our planets and comets work elsewhere too.
Space missions
- Comet Interceptor A mission that will wait in space for a pristine comet, then split into three to meet it.
Key dates
| Date | What happened |
|---|---|
| 30 August 2019 | Gennady Borisov discovered the first known interstellar comet. |
| 8 December 2019 | Comet Borisov passed closest to the Sun. |
Did you know?
Borisov found the comet in the twilight, low in the sky, where professional surveys rarely look.
It was the second interstellar object found, two years after 'Oumuamua.
Its carbon monoxide content was several times higher than in typical Solar System comets.