On August 30, 2019, amateur astronomer Gennady Borisov made a fascinating discovery when he detected a comet set on a rather odd path. From his very own MARGO observatory located in Crimea, Borisov spotted Comet C/2019 Q4 approximately 3 AU from the Sun. The Minor Planet Center announced his discovery on September 11, 2019, after follow-up observations confirmed the comet, reporting that it follows a hyperbolic path and will be nearest to the Sun (approximately 2 AU) sometime in December 2019. If confirmed, C/2019 will become the second official interstellar visitor to date, two years following the discovery of ‘Oumuamua (1I/2017~U1).
Naturally, both objects share some similarities, having traversed interstellar (possibly even galactic) space and likely originating from planetary systems, on a journey that may have lasted millions to possibly billions of years. In 2017, scientists confirmed that ‘Oumuamua originated from interstellar space. Some hesitate to assign this label to Borisov as well, though many astronomers remain convinced. Borisov’s hyperbolic trajectory suggests an extrasolar origin, which could age the object considerably. Astronomers Carlos and Raul de la Fuente Marcos put it best when describing the intruiging nature of this interstellar visitor, “Direct N-body simulations that use the latest orbit determination place C/2019 Q4 well beyond the sphere of influence of the solar system only 50,000 years ago, moving inbound at a velocity nearly 500 times higher than the escape velocity from the solar system at that distance. In this context, it is difficult to exclude an extrasolar origin for C/2019 Q4.” Source: phys.org.
Several stark differences separate ‘Oumuamua and C/2019 Borisov. Curiously, C/2019’s trajectory does not direct it toward the sun, unlike ‘Oumuamua’s during its trek in our solar system. Judging by the visible tale and composition of Borisov, astronomers reached a consensus to classify it as a comet, differentiating it from ‘Oumuamua which was observed to contain more of an asteroidal composition. The greatest differences between these two interstellar visitors lies in what phase of their journey they were discovered. ‘Oumuamua was spotted on its way out of the Solar System, offering scientists a limited window to study it, until it became too dim to observe as it sped up suddenly and vaulted out into the Cosmos. To contrast, C/2019 only just arrived within our solar system, allowing researchers the opportunity to study the #$%@ out of it.
The first two confirmed interstellar objects have been uncovered, though many estimates range for how many unconfirmed objects such as these continue to visit our Cosmic Neighborhood. Some speculate there may be at least one interstellar object within the solar system at any given moment, though our current technology limits our ability to determine this. The Large Synoptic Survey Telescope (LSST) is being designed for this very purpose: to uncover these rogue maverick space rocks and figure out where the Hades they come from. Missions to intercept an interstellar object in the future have also been proposed. Regardless, scientists are majorly stoked, bro, particularly for what else awaits on the horizon. The incoming orbit of the object appears close to the galactic plane, a fascinating concept for what that might imply.