- Interplanetary dust cloud
The interplanetary dust cloud is
cosmic dust(small particles floating in space) which pervade the space between planets in the Solar Systemand in other planetary systems. It has been studied for many years in order to understand its nature, origin, and relationship to larger bodies.
In our solar system, the dust particles not only scatter solar light (called the "
zodiacal light", which is confined to the ecliptic plane), buts also produce thermalemission, 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 orbithave typical sizes of 10-100 micrometers(Backman, D., 1997). The total mass of the interplanetary dust cloud is about the mass of an asteroidof radius 15 km (with density of about 2.5 g/cm3).
ources of interplanetary dust
The sources of interplanetary dust particles (IDPs) include at least: asteroid collisions,
cometary activity and collisions in the inner solar system, Kuiper Beltcollisions, and interstellar mediumgrains (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.
Dust particle life cycle
The main physical processes "affecting" (destruction or expulsion mechanisms) interplanetary dust particles are: expulsion by
radiation pressure, inward Poynting-Robertson (PR) radiation drag, solar windpressure (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 100,000,000 years, then the grains must have been from recently released fragments of larger objects, i.e. they cannot be leftover grains from the protoplanetary disk(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 interstellar mediumdust. All primordial grains from the Solar System's formation were removed long ago.
Particles which are affected primarily by radiation pressure are known as beta meteoroids. They are generally less than 1.4 x 10-12 g and spiral outward from the sun into interstellar space. [http://www.gps.caltech.edu/genesis/DocumentN.html#BeMe]
Interplanetary dust structures
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") (Jackson and Zook, 1988, 1992) (Dermott, S.F. et al., 1994, 1997)
Collecting interplanetary dust on earth
In 1951, Fred Whipple predicted that micrometeorites smaller than 100 micrometers in diameter might be decelerated on impact with the earth's upper atmosphere without melting [F. L. Whipple (1950) The theory of micrometeorites, part I: In an isothermal atmosphere, "Proc. Nat. Acad. Sci." 36:687-695] . The modern era of laboratory study of these particles began with the stratospheric collection flights of Brownlee and collaborators in the 1970s using balloons and then U2 aircraft [D. E. Brownlee (1978) Interplanetary dust: Possible implications for comets and presolar interstellar grains, in "Protostars and Planets" (ed. T. Gehrels, U. Arizona Press, Tucson) pp. 134-150] .
Although some of the particles found were similar to the material in present day meteorite collections, the nanoporous nature and unequilibrated cosmic-average composition of other particles suggested that they began as fine-grained aggregates of nonvolatile building blocks and cometary ice [P. Fraundorf, D. E. Brownlee, and R. M. Walker (1982) Laboratory studies of interplanetary dust, in "Comets" (ed. L. Wilkening, U. Arizona Press, Tucson) pp. 383-409.] . The interplanetary nature of these particles was later verified by noble gas [B. Hudson, G. J. Flynn, P. Fraundorf, C. M. Hohenberg, and J. Shirck (1981) Noble gases in stratospheric dust: Confirmation of extraterrestrial origin, "Science" 211:383-386.] and solar flare track [J. P. Bradley, D. E. Brownlee and P. Fraundorf (1984) Discovery of nuclear tracks in interplanetary dust, "Science" 226:1432-1434.] observations.
In that context a program for atmospheric collection, and curation, of these particles was developed at [http://curator.jsc.nasa.gov/dust/ Johnson Space Center] in Texas. This stratospheric micrometeorite collection, along with
presolar grainsfrom meteorites, are unique sources of extraterrestrial material (not to mention being small astronomical objects in their own right) available for study in laboratories today.
See: [http://astrobiology.arc.nasa.gov/workshops/zodiac/backman/backman.txt NASA Panel Report on Extrasolar Zodiacal Emission]
cite conference | author=Dermott, S.F. | title=Signatures of Planets in ZodiacalLight | booktitle=Extrasolar Zodiacal Emission - NASA Study Panel Report | year=1997 | pages=
cite conference | author=Levasseur-Regourd, A.C. | title=Optical and Thermal Properties ofZodiacal Dust | booktitle=Physics, Chemistry and Dynamics of InterplanetaryDust, ASP Conference series, Vol 104 | year=1996 | pages=301-
cite conference | author=Reach, W. | title=General Structure of the Zodiacal DustCloud | booktitle=Extrasolar Zodiacal Emission - NASA Study Panel Report | year=1997 | pages=
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