Candidates for Asteroid Dust Trails

The contribution of different sources to the circumsolar dust cloud (known as the zodiacal cloud) can be deduced from diagnostic observations. We used the Spitzer Space Telescope to observe the diffuse thermal emission of the zodiacal cloud near the ecliptic. Several structures were identified in these observations, including previously known asteroid dust bands, which are thought to have been produced by recent asteroid collisions, and cometary trails. Interestingly, two of the detected dust trails, denoted t1 and t2 here, cannot be linked to any known comet. Trails t1 and t2 represent a much larger integrated brightness than all known cometary trails combined and may therefore be major contributors to the circumsolar dust cloud.We used our Spitzer observations to determine the orbits of these trails and were able to link them to two (‘‘orphan’’ or type II) trails that were discovered by the Infrared Astronomical Satellite (IRAS ) in 1983. The orbits of trails t1 and t2 that we determined by combining the Spitzer and IRAS data have semimajor axes, eccentricities, and inclinations like those of themain-belt asteroids.We therefore propose that trails t1 and t2 were produced by very recent (P100 kyr old) collisional breakups of small,P10 km diameter main-belt asteroids.