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Dustbuster - A Cosmic Dust Analyzer - Page 1
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Introduction
Dust is an important component of the interplanetary and interstellar medium. An understanding of the evolution, dynamics, and composition of cosmic dust is vital to the understanding of planetary formation and other phenomena.
The three main approaches to studying dust are remote sensing, collection of dust from the atmosphere and surface of the Earth, and sampling dust in space. Remote sensing methods, including observations of radar, zodiacal light, and thermal emissions, are useful primarily for studying dust dynamics and distributions. Samples collected on the Earth are useful for studying composition and particle structure, but they generally have been altered by atmospheric heating. Dust grains encountered by spacecraft can either be analyzed immediately by on-board instruments (in situ) or returned to Earth for later analysis.
Infrared imagery shows dust features (green blobs)
in the direction of the center of the galaxy.
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Artist's rendering of Stardust,
a comet dust sample return mission
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Impact Ionization: in situ Sample Prep
Spacecraft encounter dust grains at very high velocities, typically 20-100 km/sec. At these velocities, dust grains and portions of the surface they hit are to some degree vaporized (or at least melted) and ionized.
The degree of ionization is dependent on the impact velocity, and is different for each chemical species. The initial energies with which ions are produced is both large and not well known, complicating analysis. For instance, in laboratory measurements of a 94 km/s, 70 nm boron carbide particle striking a silver target, carbon ions were produced with initial kinetic energies of 40 +/- 25 eV. In the same impact, though, hydrogen ions were observed with initial energies of over 100 eV (Ratcliff, PR; Allahdadi, F; "Characteristics of the plasma from a 94km/s micro-particle impact" Adv. Space Res. 17 (12) 87-91, 1996).
The impact event also produces a flash of light, the spectrum of which can be used to extract mineralogical data. It is convenient to study the dust grain composition by analyzing the ions produced in a high-velocity impact. A number of spacecraft instruments have been designed for such analysis.
Previous Instruments for in situ Dust Analysis
Numerous space instruments have made in situ measurements on dust. Some were designed to detect only the presence, size, and flux of dust, or the charge and trajectory of dust grains. Still others have included components to determine mass spectra of ionized dust grains. Mass spectrometer instruments include those such as PUMA1 and 2 (VEGA1/2), PIA (GIOTTO), the Cassini Cosmic Dust Analyzer, and the Stardust Cometary and Interstellar Dust Analyzer (CIDA).
The PUMA, PIA, and Stardust CIDA instruments are all of the same general design. In each, a reflectron provides first-order correction of the initial energies of the ions. Although reflectrons greatly improve resolution, the instruments are much too large and massive to be used on interplanetary or deep space missions.
The Stardust CIDA instrument.
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The Cassini CDA.
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