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Register a new userLinking studies of tiny meteoroids, zodiacal dust, cometary dust and circumstellar disks
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Tiny meteoroids entering the Earths atmosphere and inducing meteor showers have long been thought to originate partly from cometary dust. Together with other dust particles, they form a huge cloud around the Sun, the zodiacal cloud. From our previous studies of the zodiacal light, as well as other independent methods (dynamical studies, infrared observations, data related to Earths environment), it is now established that a significant fraction of dust particles entering the Earths atmosphere comes from Jupiter-family comets (JFCs). This paper relies on our understanding of key properties of the zodiacal cloud and of comet 67P/Churyumov-Gerasimenko, extensively studied by the Rosetta mission to a JFC. The interpretation, through numerical and experimental simulations of zodiacal light local polarimetric phase curves, has recently allowed us to establish that interplanetary dust is rich in absorbing organics and consists of fluffy particles. The ground-truth provided by Rosetta presently establishes that the cometary dust particles are rich in organic compounds and consist of quite fluffy and irregular aggregates. Our aims are as follows: (1) to make links, back in time, between peculiar micrometeorites, tiny meteoroids, interplanetary dust particles, cometary dust particles, and the early evolution of the Solar System, and (2) to show how detailed studies of such meteoroids and of cometary dust particles can improve the interpretation of observations of dust in protoplanetary and debris disks. Future modeling of dust in such disks should favor irregular porous particles instead of more conventional compact spherical particles.
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We model the infrared emission from zodiacal dust detected by the IRAS and COBE missions, with the aim of estimating the relative contributions of asteroidal, cometary and interstellar dust to the zodiacal cloud. Our most important result is the detection of an isotropic component of foreground radiation due to interstellar dust. The dust in the inner solar system is known to have a fan-like distribution. If this is assumed to extend to the orbit of Mars, we find that cometary, asteroidal and interstellar dust account for 70%, 22% and 7.5% of the dust in the fan. We find a worse fit if the fan is assumed to extend to the orbit of Jupiter. Our model is broadly consistent with the analysis by Divine (1993) of interplanetary dust detected by Ulysses and other spacecraft. Our estimate of the mass-density of interstellar dust in the inner solar system is consistent with estimates from Ulysses at 1.5 au, but is an order of magnitude higher than Ulysses estimates at r > 4 au. Only 1% of the zodiacal dust arriving at the earth would be interstellar, in our model. Our models can be further tested by ground-based kinematical studies of the zodiacal cloud, which need to extend over a period of years to monitor solar cycle variations in interstellar dust, by dynamical simulations, and by in situ measurements from spacecraft.
If planetesimal formation is an efficient process, as suggested by several models involving gravitational collapse of pebble clouds, then, before long, a significant part of the primordial dust mass should be absorbed in many km sized objects. A good understanding of the total amount of solids in the disk around a young star is crucial for planet formation theory. But as the mass of particles above the mm size cannot be assessed observationally, one must ask how much mass is hidden in bigger objects. We perform 0-d local simulations to study how the planetesimal to dust and pebble ratio is evolving in time and to develop an understanding of the potentially existing mass in planetesimals for a certain amount of dust and pebbles at a given disk age. We perform a parameter study based on a model considering dust growth, planetesimal formation and collisional fragmentation of planetesimals, while neglecting radial transport processes. While at early times, dust is the dominant solid particle species, there is a phase during which planetesimals make up a significant portion of the total mass starting at approximately $10^4 - 10^6$ yr. The time of this phase and the maximal total planetesimal mass strongly depend on the distance to the star $R$, the initial disk mass, and the efficiency of planetesimal formation $epsilon$. After approximately $10^6$ yr, our model predicts planetesimal collisions to dominate, which resupplies small particles. In our model, planetesimals form fast and everywhere in the disk. For a given $epsilon$, we were able to relate the dust content and mass of a given disk to its planetesimal content, providing us with some helpful basic intuition about mass distribution of solids and its dependence on underlying physical processes.
A clear understanding of the chemical processing of matter, as it is transferred from a molecular cloud to a planetary system, depends heavily on knowledge of the physical conditions endured by gas and dust as these accrete onto a disk and are incorporated into planetary bodies. Reviewed here are astrophysical observations of circumstellar disks which trace their evolving properties. Accretion disks that are massive enough to produce a solar system like our own are typically larger than 100 AU. This suggests that the chemistry of a large fraction of the infalling material is not radically altered upon contact with a vigorous accretion shock. The mechanisms of accretion onto the star and eventual dispersal are not yet well understood, but timescales for the removal of gas and optically thick dust appear to be a few times 10$^6$ yrs. At later times, tenuous ``debris disks of dust remain around stars as old as a few times 10$^8$ yrs. Features in the morphology of the latter, such as inner holes, warps, and azimuthal asymmetries, are likely to be the result of the dynamical influence of large planetary bodies. Future observations will enlighten our understanding of chemical evolution and will focus on the search for disks in transition from a viscous accretion stage to one represented by a gas-free assemblage of colliding planetesimals. In the near future, comparative analysis of circumstellar dust and gas properties within a statistically significant sample of young stars at various ages will be possible with instrumentation such as SIRTF and SOFIA. Well-designed surveys will help place solar system analogs in a general context of a diversity of possible pathways for circumstellar evolution, one which encompasses the formation of stellar and brown-dwarf companions as well as planetary systems.
Zodiacal emission is thermal emission from interplanetary dust. Its contribution to the sky brightness is non-negligible in the region near the ecliptic plane, even in the far-infrared (far-IR) wavelength regime. We analyse zodiacal emission observed by the AKARI far-IR all-sky survey, which covers 97% of the entire sky at arcminute-scale resolution in four photometric bands, with central wavelengths of 65, 90, 140, and 160 $mu$m. AKARI detected small-scale structures in the zodiacal dust cloud, including the asteroidal dust bands and the circumsolar ring, at far-IR wavelengths. Although the smooth component of the zodiacal emission structure in the far-IR sky can be reproduced well by models based on existing far-IR observations, previous zodiacal emission models have discrepancies in the small-scale structures compared with observations. We investigate the geometry of the small-scale dust-band structures in the AKARI far-IR all-sky maps and construct template maps of the asteroidal dust bands and the circumsolar ring components based on the AKARI far-IR maps. In the maps, $pm 1.4deg$, $pm 2.1deg$ and $pm 10deg$ asteroidal dust-band structures are detected in the 65 $mu$m and 90 $mu$m bands. A possible $pm 17deg$ band may also have been detected. No evident dust-band structures are identified in either the 140 $mu$m or the 160 $mu$m bands. By subtracting the dust-band templates constructed in this paper, we can achieve a similar level of flux calibration of the AKARI far-IR all-sky maps in the $|beta| < 40deg$ region to that in the region for $|beta| > 40deg$.
The long-term evolution of a circumstellar disk starting from its formation and ending in the T Tauri phase was simulated numerically with the purpose of studying the evolution of dust in the disk with distinct values of viscous alpha-parameter and dust fragmentation velocity v_frag. We solved numerical hydrodynamics equations in the thin-disk limit, which are modified to include a dust component consisting of two parts: sub-micron-sized dust and grown dust with a maximum radius a_r. The former is strictly coupled to the gas, while the latter interacts with the gas via friction. The conversion of small to grown dust, dust growth, and dust self-gravity are also considered. We found that the process of dust growth known for the older protoplanetary phase also holds for the embedded phase of disk evolution. The dust growth efficiency depends on the radial distance from the star - a_r is largest in the inner disk and gradually declines with radial distance. In the inner disk, a_r is limited by the dust fragmentation barrier. The process of small-to-grown dust conversion is very fast once the disk is formed. The total mass of grown dust in the disk (beyond 1 AU) reaches tens or even hundreds of Earth masses already in the embedded phase of star formation and even a greater amount of grown dust drifts in the inner, unresolved 1 AU of the disk. Dust does not usually grow to radii greater than a few cm. A notable exception are models with alpha <= 10^{-3}, in which case a zone with reduced mass transport develops in the inner disk and dust can grow to meter-sized boulders in the inner 10 AU. Grown dust drifts inward and accumulates in the inner disk regions. This effect is most pronounced in the alpha <= 10^{-3} models where several hundreds of Earth masses can be accumulated in a narrow region of several AU from the star by the end of embedded phase. (abridged).
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