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.
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.
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.
