Why are some older stars surrounded by dust? Observations from the Spitzer Space Telescope [ http://www.spitzer.caltech.edu/about/index.shtml ] by a team led by George Rieke [ http://www.as.arizona.edu/department/faculty/rieke.html ] (U. Arizona [ http://www.as.arizona.edu/ ]) were expected to show that young stars, on the order of one million years old, have large dust disks [ http://antwrp.gsfc.nasa.gov/apod/ap990120.html ], while relatively older stars, between 10 and 100 million years old, have none. The conventional wisdom [ http://cougar.jpl.nasa.gov/HR4796/anim.html ] was that the dust disks [ http://antwrp.gsfc.nasa.gov/apod/ap021011.html ] surrounding young stars were still forming planets, while in older systems these disks had dissipated after planets had already formed. Unexpectedly, they found [ http://www.spitzer.caltech.edu/Media/releases/ssc2004-17/release.shtml ] some older stars with the infrared [ http://www.us-gemini.noao.edu/public/infrared.html ] glow of impressive rings or disks of dust [ http://antwrp.gsfc.nasa.gov/apod/ap010813.html ]. A possible explanation [ http://www.spitzer.caltech.edu/Media/releases/ssc2004-17/release.shtml ] is that the old disks are remnant debris [ http://antwrp.gsfc.nasa.gov/apod/ap020724.html ] from violent collisions between many forming planets of rock. Resultant dust rings [ http://antwrp.gsfc.nasa.gov/apod/ap040825.html ] from such a scenario are depicted by an artist's illustration above [ http://www.spitzer.caltech.edu/Media/releases/ssc2004-17/ssc2004-17a.shtml ].