In the dark early morning hours before dawn on August 30, 2019, an amateur astronomer and telescope maker searched the skies for a faint smudge of light. Gennady Borisov was looking for comets. Any comet, actually. Borisov is an engineer employed by the Sternberg Astronomical Institute, part of Moscow State University. His hobby is astronomy and he’s been credited with the discovery of seven comets.
Using a telescope he himself designed and built specifically for finding comets, Borisov picked out what he was looking for low on the horizon, among countless other points of light. The fuzzy image in his telescope was exactly what he had been scanning the skies for.
Spotting this particular comet, however, has won Borisov fame among astronomers and earned him a place in science history. This comet is different from every other comet previously observed by humans, because it’s not from here. It came from interplanetary space, somewhere outside the local neighborhood of planets we call the Solar System. Astronomers already think they might be able to track it back to it’s origin.
Astronomical objects receive a series of names as they are discovered, confirmed, and finally accepted by the International Astronomical Union (IAU). Initially Borisov’s discovery was given the provisional designation of ‘gb00234’. Once confirmed as a genuine comet by other astronomers around the world, Borisov’s comet was temporarily redesignated as ‘C/2019 Q4 (Borisov)’. After it had been conclusively proven that the comet had originated from interstellar space, the IAU ultimately and permanently named the comet ‘2I/Borisov’. Fame and history, ladies and gentlemen.
Although 2I/Borisov is the first interstellar comet discovered by humans, it’s the second interstellar object of any kind that mankind has observed. Thus, the meaning of ‘2I’ is shorthand for ‘second interstellar’.
The first interstellar object discovered, 1I/’Oumuamua, was first spotted in October 2017, as it was leaving the Solar System. Unfortunately it was, practically speaking, as good as gone. Astronomers never got a good look at, although they can say it was not a comet but a rocky body. They were also able to determine conclusively that it’s orbital trajectory proved it’s extraterrestrial origin, but not where it came from.
Astronomers were much luckier with the 2I/Borisov discovery, made just as it was entering the Solar System. Studying 2I/Borisov will tell us tales about the distant system it came from, a place we can’t go visit because it would take many thousands of years to reach with current technology.
The comet is inbound at about a 40° incline to the orbits of Earth and the other planets, moving at a speed of 150,000 kilometers/hour (93,000 miles/hour) which is much faster than local comets move. Remember that Borisov found the comet low in the sky shortly before dawn? That’s because 2I/Borisov is approaching us from the opposite side of the Sun. It will be easier for earth-bound astronomers to study once it passes our home star. The Jet Propulsion Laboratory reports that, “[t]he object will peak in brightness in mid-December and continue to be observable with moderate-size telescopes until April 2020. After that, it will only be observable with larger professional telescopes through October 2020.” That’s a full year that scientists will have to study the interstellar ice ball.
At it’s closest approach, in December, it will still be outside of Mars’ orbit. The closest it will come to Earth is approximately 300 million kilometers (190 million miles), a bit more than twice the distance from the Earth to the Sun.
If you’re interested in the night sky, local amateur astronomy clubs often host star parties and invite the public to come out and take a peak at celestial bodies.
Question of the night: If you’ve ever looked through a telescope, what did you see? (The telescope needn’t have been pointed skyward).
