Identification of cometary and asteroidal particles in stratospheric IDP collections

He release temperature curves were determined for a specially processed set of 5 microns to 15 microns stratospheric IDP's whose masses, densities, and compositions were accurately measured. The He release temperature in combination with atmospheric entry calculations yields a most probable entry velocity for each particle and association with either an asteroidal (low velocity) or cometary (high velocity) origin. It was found that over half of the 5-15 microns IDP's have entry velocities consistent with asteroidal origin and that at least 20 percent have cometary origins. A few of the asteroidal particles are porous aggregates and it appears that there may be close material similarities among some primitive asteroids and comets. In the processing of individual 5 microns IDP's and determination of entry velocities, a few dozen microtome slices that can be used for a variety of detailed TEM, IR, and ion probe studies were preserved. These procedures provide laboratory samples that can be generically associated with asteroids and comets and are in a sense a limited sample return mission from these primitive bodies.