Cosmic Dust - Detection Methods

Detection Methods

Cosmic dust can be detected by indirect methods utilizing the radiative properties of cosmic dust.

Cosmic dust can also be detected directly ('in-situ') using a variety of collection methods and from a variety of collection locations. At the Earth, generally, an average of 40 tons per day of extraterrestrial material falls to the Earth. The Earth-falling dust particles are collected in the Earth's atmosphere using plate collectors under the wings of stratospheric-flying NASA airplanes and collected from surface deposits on the large Earth ice-masses (Antarctica and Greenland/the Arctic) and in deep-sea sediments. Don Brownlee at the University of Washington in Seattle first reliably identified the extraterrestrial nature of collected dust particles in the later 1970s. Another source is the meteorites, which contain stardust extracted from them (see below). Stardust grains are solid refractory pieces of individual presolar stars. They are recognized by their extreme isotopic compositions, which can only be isotopic compositions within evolved stars, prior to any mixing with the interstellar medium. These grains condensed from the stellar matter as it cooled while leaving the star.

In interplanetary space, dust detectors on planetary spacecraft have been built and flown, some are presently flying, and more are presently being built to fly. The large orbital velocities of dust particles in interplanetary space (typically 10–40 km/s) make intact particle capture problematic. Instead, in-situ dust detectors are generally devised to measure parameters associated with the high-velocity impact of dust particles on the instrument, and then derive physical properties of the particles (usually mass and velocity) through laboratory calibration (i.e. impacting accelerated particles with known properties onto a laboratory replica of the dust detector). Over the years dust detectors have measured, among others, the impact light flash, acoustic signal and impact ionisation. Recently the dust instrument on Stardust captured particles intact in low-density aerogel.

Dust detectors in the past flew on the HEOS-2, Helios, Pioneer 10, Pioneer 11, Giotto, and Galileo space missions, on the Earth-orbiting LDEF, EURECA, and Gorid satellites, and some scientists have utilized the Voyager 1 and 2 spacecrafts as giant Langmuir probes to directly sample the cosmic dust. Presently dust detectors are flying on the Ulysses, Cassini, Proba, Rosetta, Stardust, and the New Horizons spacecraft. The collected dust at Earth or collected further in space and returned by sample-return space missions is then analyzed by dust scientists in their respective laboratories all over the world. One large storage facility for cosmic dust exists at the NASA Houston JSC.

Infrared light can penetrate the cosmic dust clouds, allowing us to peer into regions of star formation and the centers of galaxies. NASA's Spitzer Space Telescope is the largest infrared telescope ever launched into space. The Spitzer Space Telescope (formerly SIRTF, the Space Infrared Telescope Facility) was launched into space by a Delta rocket from Cape Canaveral, Florida on 25 August 2003. During its mission, Spitzer will obtain images and spectra by detecting the infrared energy, or heat, radiated by objects in space between wavelengths of 3 and 180 micrometres. Most of this infrared radiation is blocked by the Earth's atmosphere and cannot be observed from the ground. The findings from the Spitzer already revitalized the studies of cosmic dust. A recent report from a Spitzer team shows some evidence that cosmic dust is formed near a supermassive black hole.