Atmospheric entry heating: A criterion to distinguish between asteroidal and cometary sources of interplanetary dust

Abstract

The detection by the Infrared Astronomy Satellite of dust trails along the paths of active comets and dust bands in the main asteroid belt suggests that both regions contribute to the interplanetary dust which makes up the zodiacal cloud. The relative proportions of the contributions from these two sources have not been established. Samples of the interplanetary dust are collected from the stratosphere by NASA sampling aircraft. Laboratory analysis of these cosmic dust particles provides information on the duration of their exposure as small particles in space and the peak temperature they reached during atmospheric entry and deceleration. These features provide clues to the orbits of the particles and thus their sources. The three-dimensional orbital evolution of dust particles from asteroidal and cometary sources, under the influence of Poynting-Robertson drag, is modeled. The space exposure ages at collection and peak temperatures reached on atmospheric entry are calculated for particles from both types of sources. The peak temperature on entry is shown to be an indicator of the dust source. Dust particles ranging from 10 to 20 μm in diameter and having a density of 1 g/cm 3 which are derived from the asteroid belt reach peak temperatures less than 700°C on atmospheric entry because of their low geocentric velocities at Earth collection. Particles from comets with perihelia greater than 1.2 AU typically experience heating in the 600 to 800°C range, while those from comets with perihelia less than 1.2 AU, long speculated to be the major source of interplanetary dust, are typically heated to temperatures above 800°C. The presence of solar flare tracks, which are believed to be erased by heating above 600°C for a few seconds, and the presence of volatile elements and minerals stable only at low temperatures in chondritic cosmic dust particles collected from the stratosphere are then used as internal indicators of the peak temperature reached. The atmospheric entry velocities inferred from all three of these indicators (tracks, volatile elements, and minerals) are consistent with a major fraction of the stratospheric cosmic dust particles being derived from parent bodies in the main asteroid belt, and indicate that the contribution from cometary sources with perihelia less than 1.2 AU, such as Comet Encke, is small.