An object cataloged as C/2019 Q4 (Borisov) and identified as a comet discovered on August 30 by the amateur astronomer Gennady Borisov has a strongly hyperbolic trajectory that suggests its interstellar origin. This could be the first identified interstellar comet, with the advantage that it was discovered while it was still approaching the Sun so it will be possible to conduct more observations for months.
Gennady Borisov is a comet hunter at the Crimean Astrophysical Observatory who might have made a historical discovery on August 30, 2019. After the announcement, other observatories started looking for it and soon realized that its trajectory indicated an anomalous orbit. Its characteristics, including its speed, make it unlikely that it’s a comet that formed at the edge of the solar system and then was projected towards the inner system because C/2019 Q4 should have received a truly remarkable boost from a large-size object, such as a planet.
Observations of the object that was cataloged as C/2019 Q4 and analysis of the data collected were also conducted by the Scout System at NASA’s JPL and ESA. A problem in assessing its origin is given by the fact that the first observations were made when it was close to the Sun in the sky and near the horizon, factors that have a negative influence on the observations’ quality. The approximations in those data will be compensated over time.
Now C/2019 Q4 is about 420 million kilometers from the Sun and the current projections of its trajectory indicate that at the beginning of December 2019 it will reach its maximum proximity to the Sun with a distance that will remain remarkable given that it’s been estimated at around 300 million of kilometers. Its speed was estimated at around 150,000 kph, much higher than those typical of objects orbiting the Sun and for this reason considered among the evidence of its interstellar origin. It also indicates that moving away from the Sun it will travel towards interstellar space.
The size of C/2019 Q4 has so far been estimated very roughly in a few kilometers across. Its cometary nature doesn’t help because even at the current distance it’s emitting dust and various particles due to the sublimation of various compounds caused by sunlight. It’s a typical cometary coma that makes it difficult to distinguish its nucleus and measure it with precision.
After the case of the interstellar asteroid later named ‘Omuamua, discovered in 2017, C/2019 Q4 offers new possibilities to study an object from another star system with the advantage that it’s larger and is still approaching the Sun. ‘Omuamua’s observations remained limited and it’s not yet clear whether it’s an asteroid or a comet, instead C/2019 Q4 has a trajectory that for several months will offer opportunities for observations. We can expect many astronomers to be interested in studying this comet so it will be in the news for a long time.