No abstract

The zodiacal dust bands are bright infrared (IR) strips produced by thermal emission from circumsolar rings of particles. Two of the three principal dust bands, known as b and g, were previously linked to the recent asteroid collisions that produced groups of fragments, so-called asteroid families, near the orbits of (832) Karin and ( 490) Veritas. The origin of the third, near-ecliptic a band has been unknown until now. Here we report the discovery of a recent breakup of a 120 km diameter asteroid near a's originally suspected source location in the Themis family. Numerical modeling and observations of the a-band thermal emission from the Spitzer Space Telescope indicate that the discovered breakup is the source of a-band particles. The recent formation of all principal dust bands implies a significant time variability of the circumstellar debris disks.

We observed comet 2P/Encke with the Infrared Space Observatory ISOCAM on