​An unusual object detected streaking across the sky last month was a comet that originated outside our solar system, observations have confirmed, becoming only the second observed interstellar object to cross into our solar system. It has been named 2I/Borisov by the International Astronomical Union's Minor Planet Center. And it's anywhere between 1.2 and 10 miles in diameter, Karen Meech and her colleagues at the University of Hawaii say.  Follow-up observations of the comet were made, including by Davide Farnocchia at NASA's Center for Near-Earth Object Studies and by the European Space Agency's Near-Earth Object Coordination Center.  We'll get a chance to know the comet better soon. It's due to enter the inner part of our solar system on October 26. To look at it right now through telescopes from Earth, the comet appears close to the sun. It will be visible through professional telescopes for months. The comet is making its way toward our sun and is now 260 million miles away. It will get closest to Earth -- 190 million miles -- on December 8.
"The comet's current velocity is high, about 93,000 mph, which is well above the typical velocities of objects orbiting the Sun at that distance," Farnocchia said. "The high velocity indicates not only that the object likely originated outside our solar system but also that it will leave and head back to interstellar space."  ​"The object will peak in brightness in mid-December and continue to be observable with moderate-size telescopes until April 2020," Farnocchia said. "After that, it will only be observable with larger professional telescopes through October 2020."