Interplanetary dust particle
An interplanetary dust particle (IDP) is a microscopic grain of cosmic dust collected in Earth's upper atmosphere before it reaches the ground.
Interplanetary dust particles, or IDPs, are extraterrestrial grains typically a few to a few tens of micrometres across. Because they are so small and light, many decelerate high in the atmosphere without melting fully, then drift slowly downwards. Since the 1970s, high-flying research aircraft have captured them in the stratosphere, roughly 20 kilometres up, on collectors coated with silicone oil, before they mix with terrestrial dust.
IDPs are split broadly into smooth, hydrated particles resembling the matrix of CI and CM chondrites, and chondritic porous IDPs: fluffy aggregates of anhydrous minerals, carbon-rich material and GEMS (glass with embedded metal and sulfides). The porous type has very high abundances of presolar grains and isotopically anomalous organic matter, and is widely thought to come from comets. Comparison with grains returned from Comet Wild 2 by NASA's Stardust mission in 2006 supports links between comets and some anhydrous IDPs.
No conventional meteorite is an IDP, so examples are catalogued by collection number. They are studied with electron microscopy, nanoscale secondary ion mass spectrometry and synchrotron techniques, working on grains far too small to see with the naked eye.
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