Astronomers using the NASA/ESA Hubble Space Telescope have captured two new images of 2I/Borisov, the first known interstellar comet to travel through the Solar System. Nevertheless, the interstellar comet is ripe for study using world-class telescopes, including the Hubble Space Telescope, which imaged the comet as it rounded the Sun. It travelled at speeds of more than 175,000kph, making it one of the fastest comets ever seen, and it remains one of only two objects known to have passed through our solar system. The bright smear on the left side of the image is the distant spiral galaxy 2MASX J10500165-0152029.
The second image, captured on December 9, 2019, is Hubble's revisit observation of the comet near its closest approach to the Sun. A gravitational interaction between these comet-like objects and other massive bodies could cause them to hurtle deep into space where they go adrift among the stars. It was approximately 203 million miles from Earth when the image was taken on November 16. The comet's light is artificially colored blue (it's actually a grayscale image) to help distinguish detail.
Since back in October, the space telescope has been following this celestial object and Hubble revealed that "the heart of the comet, a loose agglomeration of ices and dust particles, is likely no more than about 3,200 feet across, about the length of nine football fields", as the online publication mentioned above puts it. The comet is 298 million kilometres from Earth in this photo, near the inner edge of the asteroid belt. The galaxy that can be seen in a November 16 image - known as 2MASX J10500165-0152029 - looks fuzzy because Hubble was tracking the comet instead.
These shots allowed the team to calculate the size of its nucleus - the solid chunk of ice and dust in the very center. The bright central part is a comma composed of dust that leaves the surface.
Jewitt said its precise point of origin is unknown.
"Surprisingly, our Hubble images show that its nucleus is more than 15 times smaller than earlier investigations suggested it might be, Jewitt said, adding that its diameter is only about 6/10 of a mile". Knowing the size is potentially useful for beginning to estimate how common such objects may be in the solar system and our galaxy.
2I/Borisov is only the second known interstellar visitor to swoop through our backyard.
Amateur astronomer Gennady Borisov first discovered 2I/Borisov in August 2019.
However, observations from numerous telescopes show that the chemical composition of the comet is similar to that of comets that are within our solar system, which provides evidence that comets also form around other stars. By mid-2020, it will zoom past Jupiter on its way back into interstellar space, where it will drift for billions of years.