Abstract
2I/Borisov is the second ever interstellar object (ISO). It is very different from the first ISO ’Oumuamua by showing cometary activities, and hence provides a unique opportunity to study comets that are formed around other stars. Here we present early imaging and spectroscopic follow-ups to study its properties, which reveal an (up to) 5.9 km comet with an extended coma and a short tail. Our spectroscopic data do not reveal any emission lines between 4000–9000 Angstrom; nevertheless, we are able to put an upper limit on the flux of the C2 emission line, suggesting modest cometary activities at early epochs. These properties are similar to comets in the solar system, and suggest that 2I/Borisov—while from another star—is not too different from its solar siblings.
Highlights
2I/Borisov was first seen by Gennady Borisov on 30 August 2019
As more observations were conducted in the few days, there was growing evidence that this might be an interstellar object (ISO), especially its large orbital eccentricity
The first astrometric measurements do not have enough timespan and are not of same quality, the high eccentricity is yet to be confirmed. This had all changed by 11 September; where more than 100 astrometric measurements over 12 days, Ref [1] pinned down the orbit elements of 2I/Borisov, with an eccentricity of 3.15 ± 0.13, confirming the interstellar nature
Summary
2I/Borisov was first seen by Gennady Borisov on 30 August 2019. As more observations were conducted in the few days, there was growing evidence that this might be an interstellar object (ISO), especially its large orbital eccentricity. We note that unlike ’Oumuamua, 2I/Borisov was spotted very early on It was at a distance of ∼3 a.u. on 30 August, and the existence of a short tail indicates that its cometary activities just started, and we can still probe the pristine material on its surface. We expect, as this interstellar comet is on its way in (perihelion at ∼2 a.u.), that the tail will develop further. We present early observations, at the epoch of 17 September 2019 UT
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