Is another interstellar visitor going?

Astronomers have discovered a potentially interstellar object – the second after – Oumuamua – and this one is a comet that will pass closer to the Sun later this year.

There was first Uumuamua, discovered almost two years ago. We could now expect another interstellar flight, this time by the recently discovered comet, known for the moment by the provisional designation C / 2019 Q4 (Borisov) – formerly gb00234. Gennady Borisov captured the object on August 30, 2019 at the Crimean Astrophysical Observatory while it was about 3 astronomical units (a.u.) of the Sun. Unlike 'Oumuamua, which was only spotted well after perihelion, the new comet approaches the plan of the solar system and will reach perihelion on December 10, 2019.

But it's still early. Do not be surprised if these dates change as more observations arrive.

What distinguishes C / 2019 Q4 from almost all other comets is the eccentricity of its orbit. Eccentricity measures the degree of deviation of an orbit from a perfect circle whose eccentricity is equal to 0. Elliptical orbits, typical of planets, asteroids, and comets, have eccentricities between 0 and 1. Parables are equal to 1 and the eccentricities are greater than 1. a hyperbolic orbit.

In the few days after his discovery, after which he was given the temporary designation gb00234, observers cautiously discussed the possibility of interstellar origin. The chances of finding it in the pre-discovery images are slim, because for a few months, the comet is too close to the Sun to have been swept away by vast surveys. But it is expected to remain visible for many months before and after approaching Earth in December, and more position measurements will tighten the orbital fit – and provide a stronger argument for interstellar origin.

Meanwhile, the images show that the incoming object has a faint but distinct tail – something was missing in Oumuamua – and therefore appears to be a comet. Astronomers are undoubtedly eager to obtain the spectrum of the new discovery to determine which compounds might escape from its surface.

According to current observations, the eccentricity of C / 2019 Q4 is about 3.2 – definitely hyperbolic. Objects in hyperbolic orbits are not linked to the Sun. They are more likely to come from beyond the solar system, flying very long distances to make a brief visit to our neighborhood before leaving for unknown parts.

If this result holds, astronomers have an unprecedented opportunity to study a potentially interstellar object in great detail over a long period of time. According to the current magnitude (~ 18) of the comet and its distance to the Sun (2.7 a.u.), it seems to be a fairly large object – perhaps 10 km or more, depending on the reflectivity of its surface.

Assuming that the hyperbolic orbital solution of the comet is maintained, the comet appears to come from the direction of the galactic plane in Cassiopeia. Tonight (September 11-12), the object is located about 1 ° northeast of Iota (ι) Cancri and is moving slowly southeast.

At this point, it's unclear if this becomes visible in amateur telescopes, but it might become clear enough to be captured by astrophotographers. We will have updates when additional comments and photos arrive. For current positions and the current orbital element, see the latest Minor Planet Center MPEC 2019-R106 flyer.

Here's an astonishing fact: the discoverer, Gennady Borisov, is an amateur astronomer who works as an engineer at the Sternberg Astronomy Institute. He makes his own telescopes to hunt comets and has discovered seven with several NEOs. He recently completed a new 0.65 meter telescope, the instrument with which he discovered the new object.

The designation C / 2019 T4 (Borisov) will probably remain provisional until the orbit is safer. The name of the first interstellar object discovered, IO 'Oumuamua, evolved from C / 2017 U1 to A / 2017 until it finally received the designation I for "interstellar". If the new comet proves that it is roaming among another star system, it could well become 2I.