Astronomers have used NASA’s Hubble Space Telescope to capture new images of comet 2I/Borisov, the second confirmed interstellar object to be found in our Solar System, in search of some of its greatest secrets.
Led by David Jewitt from the University of California, Los Angeles, a team has been using the power of Hubble to image the comet found in late August 2017 as it makes our way into the Solar System. Images were taken on the night of Saturday, October 12 on the first four of seven orbits of the telescope allocated to this particular observation.
The images confirm many of the details we’ve known so far. The object is quite clearly a comet, with a significant amount of dust and gas being emitted from its surface. As it gets closer to the Sun we are expecting this activity to increase, peaking on December 7 when it makes its closest approach to the Sun at about two times the Earth-Sun distance, or two AU (astronomical units).
However, Jewitt and his team will use these images to try and work out the size of the nucleus of the comet, which is the hard core around which the coma of dust and gas swirls. At the moment estimates for the comet’s size range from about 700 meters to several kilometers, and getting a handle on it could tell us more about how these objects form and evolve.
Comet 2I/Borisov is known to have originated from another solar system, based on its trajectory through our own Solar System that is unbound to our Sun. While some tentative attempts have been made to pinpoint its origin, suggesting a system called Kruger-60 about 13 light-years away, the complexities involved in mapping back this trajectory in time mean we might never know for sure.
But studying the object could give us our best ever insight into an alien solar system. Our first interstellar visitor, the asteroid-like ‘Oumuamua, was spotted in late 2017 on its way out of the Solar System, giving us just weeks to observe it. This, coupled with its lesser activity, means many of its secrets went undiscovered.
Comet 2I/Borisov on the other hand will be peaking in activity in less than two months, while it is expected to remain visible in our night skies for about a year. Aside from learning its size, shape, and rotation speed, astronomers are also hoping to work out what it is made of – including looking for how much water the comet’s ices hold, if much at all. Some rare comets in our Solar System are unusually rich in carbon monoxide, for example.
At the moment the comet looks just like any other comet in our own Solar System, a fascinating discovery in itself that may suggest other systems are fairly similar. Comets, the icy remnants of a planetary system’s formation, have long been thought to be potential carriers of water and even the building blocks of life to young protoplanets in a star system.
So comet 2I/Borisov represents a hugely exciting opportunity for astronomers and non-astronomers alike. It will give us our greatest ever glimpse into an alien solar system, and coupled with ongoing research into exoplanets, could tell us more about whether worlds like Earth are rare or common in the universe.
These latest images from Hubble give us a fascinating new insight into this interstellar marvel. With many of the world’s most powerful telescopes also training their eyes in its direction, and its dazzling moment in the Sun’s spotlight not far away, its secrets will not remain unknown for much longer.