Comet 17-P Holmes now in the Outer Solar System

Spitzer's infrared picture at left hand side of this frame reveals fine dust particles that make up the Outer Shell, or "Coma", of the Comet. The Nucleus of the Comet is within the bright whitish spot in the center, while the yellow area shows solid particles that were blown from the Comet in the explosion.
The Comet is headed away from the Sun, which lies beyond the right-hand side of these pictures.

The contrast-enhanced picture on the right shows the Comet's Outer Shell, and strange "filaments", or "Streamers", of dust. The Streamers and shell are a yet another mystery surrounding Comet Holmes. Scientists had initially suspected that the Streamers were small dust particles ejected from fragments of the Nucleus, or from hyerpactive jets on the Nucleus, during the October 2007 explosion.
If so, both the Streamers and the Shell should have shifted their orientation as the Comet followed its orbit around the Sun.
Radiation pressure from the Sun should have swept the material back and away from it. But pictures of Comet Holmes taken by Spitzer over time show the Streamers and Shell in the same configuration, and not pointing away from the Sun. The observations have left astronomers stumped.

The horizontal line seen in the contrast-enhanced picture is a trail of debris that travels along with the Comet in its orbit.

The Spitzer picture was taken with the Spacecraft's multiband imaging photometer at an infrared wavelength of 24 microns.