Poster Version (Figure 1)
NASA's Spitzer Space Telescope captured the picture on the left of comet
Holmes in March 2008, five months after the comet suddenly erupted and
brightened a millionfold overnight. The contrast of the picture has been
enhanced on the right to show the anatomy of the comet.
Every six years, comet 17P/Holmes speeds away from Jupiter and heads
inward toward the sun, traveling the same route typically without
incident. However, twice in the last 116 years, in November 1892 and
October 2007, comet Holmes mysteriously exploded as it approached the
asteroid belt. Astronomers still do not know the cause of these eruptions.
Spitzer's infrared picture at left hand side of figure 1, 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 figure 1.
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.
