Dusty Planetary Systems

Extensive photometric stellar surveys show that many main-sequence stars show emission at infrared and longer wavelengths that is in excess of the stellar photosphere; this emission is thought to arise from circumstellar dust. The presence of dust disks is confirmed by spatially resolved imaging at infrared to millimeter wavelengths (tracing the dust thermal emission) and at optical to near-infrared wavelengths (tracing the dust scattered light). Because the expected lifetime of these dust particles is much shorter than the age of the stars ( > 1 ⁷ year), it is inferred that this solid material not primordial, i.e., the remaining from the placental cloud of gas and dust where the star was born, but instead is replenished by dust-producing planetesimals. These planetesimals are analogous to the asteroids, comets, and Kuiper belt objects (KBOs) in our solar system that produce the interplanetary dust that gives rise to the zodiacal light (tracing the inner component of the solar system debris disk). The presence of these "debris disks" around stars with a wide range of masses, luminosities, and metallicities, with and without binary companions, is evidence that planetesimal formation is a robust process that can take place under a wide range of conditions.