Explanation: The sixth closest asteroid encounter on record, the May 29 near-miss by the object catalogued as “2012 KT42”, was tracked by the NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii as it whizzed inside the orbital distance of Earth geosynchronous satellites (6.6 Earth radii or an altitude of 22,000 miles). KT42's discovery by the Catalina Sky Survey 23 hours before closest approach allowed time to trigger a preplanned “Rapid Response Program” involving an international team of astronomers led by MIT. Near-infrared spectral color measurements obtained simultaneously with the facility spectrograph (SpeX) while tracking the asteroid reveal a color signature interpreted as a carbon-rich composition (perhaps analogous to carbonaceous chondrite meteorites) from which a moderately dark reflectivity (albedo) is inferred. By knowing both the reflectivity and visible brightness of the object, the deduced size is about 7 meters (23 feet) across (roughly the size of a “Duck Boat”). Had 2012 KT42 actually struck the Earth, its relatively small size and likely weak structure would have made survivable atmospheric passage doubtful with perhaps only a few fragments reaching the surface as meteorites. The presented movie shows the NASA telescope first acquiring, then “locking on target” and tracking with the asteroid as it whizzes across the sky — hence stars appear only as passing streaks. The movie is compiled from 2-second exposures obtained by the MORIS camera played back at 15 frames per second. (Thus the movie plays at about 30 times actual speed.) An internal reflection within the camera can be seen faintly to the left. Frequent up/down jumps of the image are normal telescope motions as part of the spectral data collection process.
(Where subscript characters are available the designation is properly written 2012 KT42.)