Exozodiacal dust is 1–100 micrometre-sized grains of

amorphous carbon Amorphous carbon is free, reactive carbon that has no crystalline structure. Amorphous carbon materials may be stabilized by terminating dangling-π bonds with hydrogen. As with other amorphous solids, some short-range order can be observed. Amor ...

and silicate dust that fill the plane of extrasolar planetary systems. It is the exoplanetary analog of zodiacal dust, the 1–100 micrometre-sized dust grains observed in the solar system, especially interior to the asteroid belt. As with the zodiacal dust, these grains are probably produced by

outgassing Outgassing (sometimes called offgassing, particularly when in reference to indoor air quality) is the release of a gas that was dissolved, trapped, frozen, or absorbed in some material. Outgassing can include sublimation and evaporation (which ...

comets, as well as by collisions among bigger parent bodies like asteroids. Exozodiacal dust clouds are often components of

debris disk A debris disk (American English), or debris disc (Commonwealth English), is a circumstellar disk of dust and debris in orbit around a star. Sometimes these disks contain prominent rings, as seen in the image of Fomalhaut on the right. Debris di ...

s that are detected around

main-sequence star In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hert ...

s through their excess infrared emission. Particularly hot exozodiacal disks are also commonly found near spectral type A-K stars. By convention, exozodiacal dust refers to the innermost and hottest part of these debris disks, within a few

astronomical unit The astronomical unit (symbol: au, or or AU) is a unit of length, roughly the distance from Earth to the Sun and approximately equal to or 8.3 light-minutes. The actual distance from Earth to the Sun varies by about 3% as Earth orbits ...

s of the star. How exozodiacal dust is so prevalent this close to stars is a subject of debate with several competing theories attempting to explain the phenomenon. The shapes of exozodiacal dust clouds can show the dynamical influence of

extrasolar planet An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...

s, and potentially indicate the presence of these planets. Because it is often located near a star's

habitable zone In astronomy and astrobiology, the circumstellar habitable zone (CHZ), or simply the habitable zone, is the range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressure.J. F. Kast ...

, exozodiacal dust can be an important noise source for attempts to image terrestrial planets. Around 1 in 100 stars in the nearby solar systems shows a high content of warm dust that is around 1000 times greater than the average dust emission in the 8.5–12 μm range.

Formation

Although such dust was initially theoretical, we have now observed its infrared signature while attempting to observe exo-earths. As exozodiacal dust is the extrasolar equivalent of zodiacal dust, its formation is theorized to be the same. This is to be contrasted with interstellar dust, which is not trapped in a solar system. Leftover particulates from the formation of a solar system, as well as debris from the collisions of larger objects leave behind exozodiacal dust. The amount of potential exozodiacal dust is thought to be ever-decreasing, though, as massive bodies like planets absorb significant amounts of it. For instance, the earth absorbs 40,000 tons of this dust every year. The dust emits infrared radiation, and through gravitational interactions with bodies such as the sun it forms infrared rings. These rings have been observed across many solar systems throughout the Milky Way. Dust from different sources, such as from asteroid collisions, comets, and trapped particulates, are theorized to form different infrared structures, respectively.

Examples of stars with exozodiacal dust

* 51 Ophiuchi *

Fomalhaut Fomalhaut is the brightest star in the southern constellation of Piscis Austrinus, the "Southern Fish", and one of the brightest stars in the night sky. It has the Bayer designation Alpha Piscis Austrini, which is Latinized from � ...

Tau Ceti Tau Ceti, Latinized from τ Ceti, is a single star in the constellation Cetus that is spectrally similar to the Sun, although it has only about 78% of the Sun's mass. At a distance of just under from the Solar System, it is a rela ...

Vega Vega is the brightest star in the northern constellation of Lyra. It has the Bayer designation α Lyrae, which is Latinised to Alpha Lyrae and abbreviated Alpha Lyr or α Lyr. This star is relatively close at only from the Sun, a ...

Ongoing research

Observations have found that some spectral type A-K have the infrared signatures of exozodiacal dust much closer to the star than is theorized to be possible. Within a certain circumference of the star, the dust is expected to be ground down and ejected by the star within a few years. While the dust has been confirmed to exist this close to a star, models still cannot explain its presence. Modeling the behavior of both zodiacal and exozodiacal dust is a noteworthy area of research, as the dust presents itself as noise for astronomers attempting to observe planetary bodies. If the dust can be accurately modeled, it can be subtracted out of observations of exo-earths.

References

External links

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NASA Supercomputer Shows How Dust Rings Point to Exo-Earths
{{DEFAULTSORT:Exozodiacal Dust *Exozodiacal dust Exozodiacal dust Cosmic dust Articles containing video clips