span class="large"The Helix nebula exhibits complex structure on the smallest visible scales. It is composed of gaseous shells and disks puffed out by a dying sun-like star./spanbr/br/br/span class="large"In this new image from NASA's Spitzer Space Telescope, "cometary knots" show blue-green heads caused by excitation of their molecular material from shocks or ultraviolet radiation. The tails of the cometary knots appear redder due to being shielded from the central star's ultraviolet radiation and wind by the heads of the knots./spanbr/br/br/span class="large"This image was captured by the telescope's infrared array camera. The false color composite depicts wavelengths of 3.6 microns (blue), 4.5 microns (green), and 8.0 microns (red). The color saturation has been increased to intensify hues./span