A new image from NASA’s Hubble Space Telescope provides important new details about the first interstellar comet astronomers have seen in our solar system. “Data from the Hubble Space Telescope give us the best measure of the size of comet 2I/Borisov’s nucleus, which is the really important part of the comet,” said EPSS's David Jewitt, who analyzed and interpreted the data from the new image along with former student Man-To Hui and several others. Surprisingly, the nucleus is tiny, with a radius less than about 500 meters. That is important because knowing its size helps us to determine the total number, and mass, of other similar objects. Jewitt estimates that similar objects strike Earth about once every 100 Myr to 200 Myr.