The discovery of the first interstellar comet is a very important event in itself, but many details of subsequent observations of the comet itself are also significant for science. By December 2019, it should be about 150-160 million kilometers closer to Earth, with the distance from the comet to the Sun being close to 300 million kilometers.
At this distance, the radiation of our star will heat the "alien" enough to begin to actively evaporate almost all the volatile components. This is frozen carbon monoxide, carbon dioxide, water vapor, perhaps methane and much more. On the specific composition of comas, it will be possible to make unique observations and understand how the composition of comets in other planetary systems differs from the composition of their counterparts from our system.
This is particularly interesting because some solar system objects have long been suspected of being of "non-local" origin. For example, the BZ509 asteroid 2015, discovered in 2015, is orbiting in a very similar orbit to the Jupiterian one, but in the opposite direction. In theory, all objects formed from a protoplanetary disk should rotate in the same direction as the disk that generated them. If a body rotates "against the wool", there is a high probability that a migrant body once captured by the gravity of the Sun and its planets is in front of us.
If the analysis of Borisov"s comet spectra shows the similarity of its composition to the same 2015 BZ509, in contrast to the composition of other comets in our system, it will be much easier to identify the captured interstellar asteroids and comets within our system. Knowing their origin, it will be possible to send robotic probes there, as it was done with the asteroid Itokawa or comet Churyumov-Gerasimenko. On-site research can bring much more detail than any other, even the most careful study of images of interstellar travelers. Understanding how the composition of bodies outside our system differs from local ones and how much easier it will be to understand the evolution of planetary systems as a whole.
Also, the very frequency of detection of interstellar objects passing through the inner regions of the solar system is a very important parameter that allows us to assess several points at once. For example, it will be possible to understand the total number of comets typical of other stellar systems. It is possible to calculate the probability of the Sun"s capture of interstellar bodies by the Sun, but as long as we do not know the number of such bodies in the galactic space around us, these calculations are not very useful.
How often do objects from other star systems bombard the Earth?
Finally, the question of interstellar comets and asteroids has another, very mundane side: the safety of our planet. An asteroid or comet from our system can rarely sneak up on the Earth unnoticed. Like the Earth, they rotate around the Sun, and so their orbits are closed: they fly an ellipse or even a circle. That"s why "local" people are getting closer to us gradually, flying closer and closer over and over again, due to the impact of gravity of our planet on their trajectory.
And this means that they can almost not hit suddenly: NASA in advance tracks their trajectories and possible dates of intersection with the Earth. Over the years, or even decades, to get closer to any dangerous body can be prepared, to organize a parcel to it nuclear warhead (Russian researchers have already calculated such a scenario), which could reject even a large asteroid from the dangerous course.
This is not the case with "interstellar" asteroids and comets. Let"s imagine for a second that the path C/2019 Q4 would accidentally cross the Earth. Having opened the comet on August 30 and only by September 12, having found out its trajectory, the earthlings would have had very little time before the December collision (it is in December that the comet of Borisov will come to us at the minimum distance). In three or four months it is impossible to prepare an expedition capable of rejecting the trajectory of another celestial body.
And this is not just a theory. After 2018, and the discovery of the asteroid 1I/Oumoamois, astronomers tried to find in the trajectories of celestial bodies that had recently fallen to Earth, such as those that would have a great eccentricity of orbit, indicating the origin of another system. It turned out that in 2014, one such meteoroid exploded in the atmosphere over Papua New Guinea. Its size was only 0. 9 meters, so it gave only a bright flash in the stratosphere and zero surface damage.
But it could have been a much larger object, and as we remember, an asteroid ten kilometers in diameter when hitting the Earth would have produced an explosion of 100 million megatons. Sixty-six million years ago, an explosion of this magnitude killed all kinds of large land creatures on our planet. It would, therefore, be very interesting to know how often large bodies like Borisov"s comet or 1I/Oumouamois fly into our system. If they do this often enough, humanity should think in advance of the means of defense against them.