Last September, when a tiny asteroid drifted into Earth’s vicinity, our planet’s gravity captured it. The meter-size object, designated 6R10DB9, is now making its third wide swing around Earth. It was quite faint, magnitude 19.3, when discovered September 14th with the 0.68-meter (27-inch) Schmidt telescope of the Catalina Sky Survey in Arizona, and it won’t get much brighter than that. “Certainly 6R10DB9, with a geocentric eccentricity less than 1, is currently orbiting the Earth ,” says Gareth V. Williams of the Minor Planet Center, “although it will leave the Earth-Moon system after next June’s perigee.” Williams’s calculations show that prior...