A Moon-orbiting camera briefly shuddered — then got back to work — when it was hit by a tiny bit of space rock no bigger than a pinhead.It's inescapable that, left in space long enough, anything and everything will be struck by bits of interplanetary debris. And so it was that at 21:18:48.404 Universal Time on October 14, 2014, during its 23,986th orbit of the Moon, NASA's Lunar Reconnaissance Orbiter got whacked.
Fortunately, even though the attacking particle was moving very fast, perhaps 7 km per second, it wasn't large — just an estimated 0.8 mm across and 1⁄1,000 of a gram. In fact, LRO personnel back on Earth might never have known about the strike were it not for a swatch of zigzag jitter seen in one of its images — evidence that was only recently discovered once someone inspected the archived file. No other sensors recorded an anomaly at that moment, and the spacecraft wasn't moving its solar-cell panels or antenna.
Instead, it appears that the one of the craft's two telephoto cameras took a tiny hit on the big, scoop-shaped radiator that helps cool the camera's detector.
"The meteoroid was traveling much faster than a speeding bullet," says Mark Robinson (Arizona State University), who leads the Lunar Reconnaissance Orbiter Camera team. "In this case, LROC did not dodge a speeding bullet, but rather survived a speeding bullet!"
LROC's telephoto cameras build up images one line at a time as the spacecraft coasts high above the lunar surface. As shown here, the image scan started fine but then briefly recorded a zigzag pattern about 10 pixels wide. That corresponds to an angular jitter of roughly 1 arcsecond (1⁄3600°). At the time, LRO was recording a strip of lunar terrain on the Moon's farside, just to the northwest of Mare Orientale.