English: This is an image of a glowing red hot pellet of plutonium-238 dioxide to be used in a radioisotope thermoelectric generator for either the Cassini mission to Saturn or the Galileo mission to Jupiter. This image was provided by the Department of Energy via email and was taken at the Department's Los Alamos National Laboratory. Each pellet produces 62 watts of heat and when thermally isolated, can glow brilliant orange. Excerpt from email:

The pellet is glowing red because of the heat generated by the radioactive decay (primarily alpha) of the fuel. [Photos of glowing pellets are typically taken after insulating the pellet under a graphite blanket for a period of time (minutes), removing the blanket, and taking the picture.] These pellets were used in the RTGs that powered NASA's Galilleo and Cassini spacecraft on missions to Jupiter and Saturn, respectively. The pictures now being sent back from Saturn by the Cassini orbiter are made possible through this unique fuel source. To view the pictures from Saturn you may visit the NASA web site at www.jpl.nasa.gov/cassini. To read more about the General Purpose Heat source, please visit the Department of Energy website at http://nuclear.gov/space/space-desc.html ^[note] Also, I am attaching another image of a Pu-238 fuel pellet that might be of better resolution that the one shown in the link below. If you use either of the images, please attribute it to the Los Alamos National Laboratory.

^[note] Dead link, new web page at http://www.nuclear.energy.gov/space/neSpace2g.html