Don't panic, but our planet is under constant bombardment by objects of an alien origin. No, Marvin the Martian hasn't been lobbing explosive space modulators our way. Instead, it's the tens of thousands of space rocks that take aim at the Earth each year. Before you start digging a shelter, know that only about 500 of these meteorites make it through the atmosphere. Most end up in the ocean, and the ones making landfall are too small to be considered "planet killers." See for yourself at Arizona State University's Meteorite Gallery, which offers close encounters with these emissaries from across our solar system. Located on the second floor of the Interdisciplinary Science and Technology Building 4, it features a curated display of rocks from the collection of ASU's Center for Meteorite Studies, which includes more than 10,000 samples. Arranged in a half-dozen or so glass cases, these meteorites vary in size, shape, color, and composition. Some are hunks of craggy and porous rock as big as a basketball. Others are as small as pebbles or skipping stones. You might even see one of triangular chunks of the lunar surface that landed in Oman in 1999. Before you ask, no, it's not made of cheese.