At first, A/2017 U1 looked like any other asteroid. But a study of its trajectory showed that it came from another star system. Now astronomers are racing (no pun intended) to study it, because it’s moving away from Earth faster than probes can travel. (Ed Lu, San Fran, Dec 2014; Erika DeBenedictis, Vienna, Jul 2013; Dan Durda, Washington, D.C., May 2007)