Interplanetary dust cloud

The interplanetary dust cloud, or zodiacal cloud, consists of cosmic dust (small particles floating in outer space) that pervades the space between planets within planetary systems such as the Solar System. This system of particles has been studied for many years in order to understand its nature, origin, and relationship to larger bodies. The interplanetary dust cloud, or zodiacal cloud, consists of cosmic dust (small particles floating in outer space) that pervades the space between planets within planetary systems such as the Solar System. This system of particles has been studied for many years in order to understand its nature, origin, and relationship to larger bodies. In our Solar System, the interplanetary dust particles have a role in scattering sunlight and in emitting thermal radiation, which is the most prominent feature of the night sky's radiation with wavelengths ranging 5–50 μm. The particle sizes of grains characterizing the infrared emission near Earth's orbit typically range 10–100 μm. The total mass of the interplanetary dust cloud is approximately the mass of an asteroid of radius 15 km (with density of about 2.5 g/cm3). Straddling the zodiac along the ecliptic, this dust cloud is visible as the zodiacal light in a moonless and naturally dark sky and is best seen toward the Sun's direction during astronomical twilight. The Pioneer spacecraft observations in the 1970s linked the Zodiacal light with the interplanetary dust cloud in Earth's solar system. The sources of interplanetary dust particles (IDPs) include at least: asteroid collisions, cometary activity and collisions in the inner Solar System, Kuiper belt collisions, and interstellar medium 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) interplanetary dust particles 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 10,000,000 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 medium dust. 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 × 10−12 g and are pushed outward from the Sun into interstellar space.