Comet 17P/Holmes Hubble image series
These images taken by the NASA/ESA Hubble Space Telescope reveal Comet Holmes' bright core. The images show that the coma, the cloud of dust and gas encircling the comet, is getting fainter over time. The coma was brightest in the 29 October image. It is two times fainter on 31 October and nine times dimmer on 4 November than during the 29 October observation.
The coma is getting fainter because it is expanding. A huge number of small dust particles were created during the comet's outburst on 23 October. Since then those particles have been moving away from the nucleus in the interplanetary space. The coma therefore is becoming more diffuse over time.
The nucleus, however, is still active and is producing a significant amount of new dust. So the region around the nucleus is still much brighter (at least 10 times brighter) than it usually is at this point in the comet's orbit.