DULUTH — The Hubble Space Telescope is always up to something. Now, a German-led group of astronomers have observed a one-of-a-kind object in the asteroid belt between Mars and Jupiter. Scratch that. Two-of-one-kind: a pair of asteroids orbiting each other that show comet-like features including a bright coma and a long tail. It's the first known binary asteroid also classified as a main-belt comet. The team's research was published in the journal Nature recently.