Interplanetary dust cloud
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The interplanetary dust cloud has been studied for many years in order to understand its nature, origin, and relationship to planetary systems (our own, as well as extrasolar systems).
The interplanetary dust particles (IDPs) not only scatter solar light (called the "zodiacal light", which is confined to the ecliptic plane), the IDPs also produce thermal emission, which is the most prominent feature of the night-sky light in the 5-50 micrometer wavelength domain (Levasseur-Regourd, A.C. 1996). The grains characterizing the infrared emission near the earth's orbit have typical sizes of 10-100 micrometers (Backman, D., 1997). The total mass of the interplanetary dust cloud is about the mass of an asteroid of radius 15 km (with density of about 2.5 g/cm3).
The sources of IDPs include at least: asteroid collisions, cometary activity and collisions in the inner solar system, Kuiper Belt collisions, and interstellar medium (ISM) grains (Backman, D., 1997). Indeed, one of the longest-standing controversies debated in the interplanetary dust community revolves around the relative contributions to the interplanetary dust cloud from asteroid collisions and cometary activity.
The main physical processes "affecting" (destruction or expulsion mechanisms) IDPs are: expulsion by radiation pressure, inward Poynting-Robertson (PR) radiation drag, solar wind pressure (with significant electromagnetic effects), sublimation, mutual collisions, and the dynamical effects of planets (Backman, D., 1997).
The lifetimes of these dust particles are very short compared to the lifetime of the Solar System. If one finds grains around a star that is older than about 10^8 years, then the grains must have been from recently released fragments of larger objects, i.e. they cannot be leftover grains from the protoplanetary nebula (Backman, private communication). Therefore, the grains would be "later-generation" dust. The zodiacal dust in the solar system is 99.9% later-generation dust and 0.1% intruding ISM dust. All primordial grains from the Solar System's formation have been removed long ago.
The interplanetary dust cloud has a complex structure (Reach, W., 1997). Apart from a background density, this includes:
- At least 8 dust trails -- their source is thought to be short-period comets.
- A number of Dust bands, the sources of which are thought to be asteroid families in the main asteroid belt. The three strongest bands arise from the Themis family, the Koronis family, and the Eos family. Other source families include the Maria, Eunomia, and possibly the Vesta and/or Hygiea families (Reach et al 1996).
- at least 2 resonant dust rings are known (for example, the Earth-resonant dust ring, although every planet in the solar system is thought to have a resonant ring with a "wake") (Dermott, S.F. et al., 1994, 1997)
[edit] References
Backman, Dana (1997). "Exozody Workshop, NASA-Ames, October 23-25, 1997". Extrasolar Zodiacal Emission - NASA Study Panel Report.
See: [1]
Dermott, S.F. Jayaraman, S., Xu, Y.L., Gustafson, A.A.S., Liou, J.C., (June 30, 1994). "RA circumsolar ring of asteroid dust in resonant lock with the Earth". Nature 360: 79-?.
Dermott, S.F. (1997). "Signatures of Planets in Zodiacal Light". Extrasolar Zodiacal Emission - NASA Study Panel Report.
Levasseur-Regourd, A.C. (1996). "Optical and Thermal Properties of Zodiacal Dust". Physics, Chemistry and Dynamics of Interplanetary Dust, ASP Conference series, Vol 104, 301-.
Reach, W. (1997). "General Structure of the Zodiacal Dust Cloud". Extrasolar Zodiacal Emission - NASA Study Panel Report.
Reach, W.T.; Franz, B.A.; Weiland, J.L. (1997). "The Three-Dimensional Structure of the Zodiacal Dust Bands". Icarus 127: 461.
