First there was ‘Oumuamua, discovered nearly two years ago. Now we might be in store for another interstellar flyby, this time by the recently discovered comet known for now by the provisional designation C/2019 Q4 (Borisov) — formerly gb00234. Gennady Borisov captured the object on August 30, 2019, at the MARGO Observatory near Nauchnij, Crimea when it was about 3 astronomical units (a.u.) from the Sun. Unlike ‘Oumuamua, which wasn’t spotted until well after perihelion, the new comet is approaching the plane of the solar system and will reach perihelion on December 10, 2019 at a distance of 1.94 a.u.
But it’s still early. Don’t be surprised if these dates change as more observations come in.
What sets C/2019 Q4 apart from nearly every other comet is the eccentricity of its orbit. Eccentricity measures how much an orbit deviates from a perfect circle, which has an eccentricity of 0. Elliptical orbits, typical of planets, asteroids and comets, have eccentricities between 0 and 1. Parabolas are equal to 1, and an eccentricity greater than 1 indicates a hyperbolic orbit.
In the few days since its discovery, after which it bore the temporary designation gb00234, observers have broached the possibility of an interstellar origin with caution. The chance of finding it in prediscovery images isn’t great, since for some months the comet has been too close to the Sun to have been swept up by wide-field surveys. But it should remain visible for many months before and after it comes closest to Earth in December, and more positional measurements will tighten the orbital fit — and make a stronger case for an interstellar origin….[ ]