First amateur astronomer to discover an interstellar object

The first amateur astronomer to discover an interstellar comet or asteroid is Gennady Borisov (UKR/RUS), who spotted comet 2I/Borisov on 30 August 2019. Borisov made the discovery using a 65-cm (2-ft 1-in) telescope he designed and built himself at MARGO, his personal observatory in Nauchny, Crimea.

Gennady Borisov's interest in space started as a love of science fiction. He became fascinated by astronomy after a small telescope he'd made at school allowed him to get a close look at the cratered landscape of the moon. He went on to study physics at Moscow State University before joining the staff of the Crimean Astronomical Station, which is located high in the hills between Simferopol and Sevastopol in Crimea.

Although he works for an observatory, he is not a professional astronomer but rather an engineer, responsible for the maintenance and operation of telescopes and instrumentation. All his discoveries were made in his spare time using his home-made GENON series of telescopes at MARGO, his private observatory. MARGO, which stands for "Mobile Astronomical Robotics GENON Observatory" (he's still working on getting the "robotic" part up and running) is located in the village of Nauchny near the Crimean Astronomical Station.

Borisov logged his initial findings with the Minor Planet Center (MPC), which is an international organization that collects observational data on objects such as asteroids and comets. The comet was given the provisional designation C/2019 Q4 and its coordinates were published to the MPC's website.

Intrigued by this new report, large observatories all over the world turned their telescopes towards the object. This included the massive 10.4-m (34-ft) Gran Telescopio Canarias in the Canary Islands and the Pan-STARRS observatory in Hawaii (which discovered the first interstellar visitor, the asteroid 1I/'Oumuamua). These observations allowed the astronomical community to get a better view of the comet and to calculate its trajectory with greater precision.

We now know that 2I/Borisov (this name was approved by the Minor Planet Center after it was confirmed to be interstellar) approached our Solar System from the direction of the constellation Cassiopeia at a speed of around 41 km/second (91,714 mph). It passed just outside the orbit of Mars (a distance of around 300 million kilometres) on 8 December 2019, with its interaction with the Sun's gravity deflecting its onward path by about 40 degrees (in astronomy terms, it has an orbital eccentricity of 3.4). It is now travelling towards the constellation Telescopium.

Unlike 1I/'Oumuamua, which was only spotted after it had made its closest approach to the Sun, 2I/Borisov was still two months away from perihelion when it was discovered. This means that the astronomical community had more time to study the object while it was still fairly close. What they've learned is that, exotic origins aside, 2I/Borisov is a surprisingly normal comet. It measures 2–3 kilometres (1.2–1.8 miles) in diameter, and is composed primarily of water ice. As it got closer to the sun, it developed a pronounced "tail" made from sublimating water ice and other molecules, just like more familiar solar system comets.

Although this is the first interstellar comet Gennady has discovered, it's not his first comet. He is credited as the discoverer of eight other comets, as well as numerous asteroids.