On the Evolution of Dust Mineralogy, From Protoplanetary Disks to Planetary Systems (original) (raw)
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IMPACT OF GRAIN EVOLUTION ON THE CHEMICAL STRUCTURE OF PROTOPLANETARY DISKS
The Astrophysical Journal, 2011
We study the impact of dust evolution in a protoplanetary disk around a T Tauri star on the disk chemical composition. For the first time we utilize a comprehensive model of dust evolution which includes growth, fragmentation and sedimentation. Specific attention is paid to the influence of grain evolution on the penetration of the UV field in the disk. A chemical model that includes a comprehensive set of gas phase and grain surface chemical reactions is used to simulate the chemical structure of the disk.
Dust amorphization in protoplanetary disks
Astronomy & Astrophysics, 2009
High-energy irradiation of the circumstellar material might impact the structure and the composition of a protoplanetary disk and hence the process of planet formation. In this paper, we present a study on the possible influence of the stellar irradiation, indicated by X-ray emission, on the crystalline structure of the circumstellar dust. The dust crystallinity is measured for 42 class II T Tauri stars in the Taurus star-forming region using a decomposition fit of the 10 micron silicate feature, measured with the Spitzer IRS instrument. Since the sample includes objects with disks of various evolutionary stages, we further confine the target selection, using the age of the objects as a selection parameter. We correlate the X-ray luminosity and the X-ray hardness of the central object with the crystalline mass fraction of the circumstellar dust and find a significant anti-correlation for 20 objects within an age range of approx. 1 to 4.5 Myr. We postulate that X-rays represent the stellar activity and consequently the energetic ions of the stellar winds which interact with the circumstellar disk. We show that the fluxes around 1 AU and ion energies of the present solar wind are sufficient to amorphize the upper layer of dust grains very efficiently, leading to an observable reduction of the crystalline mass fraction of the circumstellar, sub-micron sized dust. This effect could also erase other relations between crystallinity and disk/star parameters such as age or spectral type.
Dust condensation in evolving discs and the composition of planetary building blocks
Monthly Notices of the Royal Astronomical Society
Partial condensation of dust from the Solar nebula is likely responsible for the diverse chemical compositions of chondrites and rocky planets/planetesimals in the inner Solar system. We present a forward physical–chemical model of a protoplanetary disc to predict the chemical compositions of planetary building blocks that may form from such a disc. Our model includes the physical evolution of the disc and the condensation, partial advection, and decoupling of the dust within it. The chemical composition of the condensate changes with time and radius. We compare the results of two dust condensation models: one where an element condenses when the mid-plane temperature in the disc is lower than the 50 per cent condensation temperature ($\rm T_{50}$) of that element and the other where the condensation of the dust is calculated by a Gibbs free energy minimization technique assuming chemical equilibrium at local disc temperature and pressure. The results of two models are generally cons...
Dust Condensation in Evolving Discs and the Composition of Meteorites, Planetesimals, and Planets
arXiv (Cornell University), 2019
Partial condensation of dust from the Solar nebula is likely responsible for the diverse chemical compositions of chondrites and rocky planets/planetesimals in the inner Solar system. We present a forward physical-chemical model of a protoplanetary disc to predict the chemical compositions of planetary building blocks that may form from such a disc. Our model includes the physical evolution of the disc and the condensation, partial advection, and decoupling of the dust within it. The chemical composition of the condensate changes with time and radius. We compare the results of two dust condensation models: one where an element condenses when the midplane temperature in the disc is lower than the 50% condensation temperature (T 50) of that element and the other where the condensation of the dust is calculated by a Gibbs free energy minimization technique assuming chemical equilibrium at local disc temperature and pressure. The results of two models are generally consistent with some systematic differences of ∼ 10% depending upon the radial distance and an element's condensation temperature. Both models predict compositions similar to CM, CO, and CV chondrites provided that the decoupling timescale of the dust is on the order of the evolution timescale of the disc or longer. If the decoupling timescale is too short, the composition deviates significantly from the measured values. These models may contribute to our understanding of the chemical compositions of chondrites, and ultimately the terrestrial planets in the solar system, and may constrain the potential chemical compositions of rocky exoplanets.
Grain growth across protoplanetary discs: 10-micron silicate feature versus millimetre slope
Context. Young stars are formed with dusty discs around them. The dust grains in the disc are originally of the same size as interstellar dust, i.e., of the order of 0.1 micron. Models predict that these grains will grow in size through coagulation. Observations of the silicate features around 10 and 20 micron are consistent with growth from submicron to micron sizes in selected sources whereas the slope of the spectral energy distribution (SED) at mm and cm wavelengths traces growth up to mm sizes and larger. Aims. We here look for a correlation between these two grain growth indicators. Methods. A large sample of T-Tauri and Herbig-Ae/Be stars, spread over the star-forming regions in Chamaeleon, Lupus, Serpens, Corona Australis, and the Gum nebula in Vela, was observed with the Spitzer Space Telescope at 5–13 micron, and a subsample was observed with the SMA, ATCA, CARMA, and VLA at mm wavelengths.We complement this subsample with data from the literature to maximise the overlap between micron and mm observations and search for correlations in the grain-growth signatures. Synthetic spectra are produced to determine which processes may produce the dust evolution observed in protoplanetary discs. Results. Dust disc masses in the range < 1 to 7 x 10^-4 MSun are obtained. The majority of the sources have a mm spectral slope consistent with grain growth. There is a tentative correlation between the strength and the shape of the 10-micron silicate feature and the slope of the SED between 1 and 3 mm. The observed sources seem to be grouped per star-forming region in the 10-micron-feature vs mm-slope diagram. The modelling results show that, if only the maximum grain size is increased, first the 10-micron feature becomes flatter and subsequently the mm slope becomes shallower. To explain the sources with the shallowest mm slopes, a grain size distribution shallower than that of the interstellar medium is required. Furthermore, the strongest 10-micron features can only be explained with bright (L ~ 6 LSun ), hot (Teff = 4000 K) central stars. Settling of larger grains towards the disc midplane results in a stronger 10-micron feature, but has a very limited effect on the mm slope. Conclusions. A tentative correlation between the strength of the 10-micron feature and the mm slope is found, which would imply that the inner and outer disc evolve simultaneously. Dust with a mass dominated by large, ~mm-sized, grains is required to explain the shallowest mm slopes. Other processes besides grain growth, such as the clearing of an inner disc by binary interaction, may also be responsible for the removal of small grains. Observations with future telescopes with larger bandwidths or collecting areas are required to provide the necessary statistics to study these processes of disc and dust evolution.
Dust in Protoplanetary Disks: A Clue as to the Critical Mass of Planetary Cores
Proceedings of The Life Cycle of Dust in the Universe: Observations, Theory, and Laboratory Experiments — PoS(LCDU2013)
Dust in protoplanetary disks is widely recognized as the building blocks of planets that are eventually formed in the disks. In the core accretion scenario, one of the standard theories of gas giant formation, the abundance of dust in disks (or metallicity, [Fe/H]) plays a crucial role in regulating the formation of cores of gas giants that proceeds via collisions of dust and planetesimals in disks. We present our recent progress on the relationship between the metallicity and planet formation, wherein planet formation frequencies (PFFs) as well as the critical mass of planetary cores (M c,crit) that can initiate gas accretion are statistically examined. We focus on three dif-* Speaker. † EACOA follow
Evidence for dust grain growth in young circumstellar disks
Science (New York, N.Y.), 2001
Hundreds of circumstellar disks in the Orion nebula are being rapidly destroyed by the intense ultraviolet radiation produced by nearby bright stars. These young, million-year-old disks may not survive long enough to form planetary systems. Nevertheless, the first stage of planet formation-the growth of dust grains into larger particles-may have begun in these systems. Observational evidence for these large particles in Orion's disks is presented. A model of grain evolution in externally irradiated protoplanetary disks is developed and predicts rapid particle size evolution and sharp outer disk boundaries. We discuss implications for the formation rates of planetary systems.
2005
Silicate dust entering the solar nebula was overwhelmingly amorphous based on studies of the current interstellar grain population. Moreover, no global high temperature event could have crystallized the dust in the nebula without also destroying the very fragile, noble-gas-rich, carbonaceous presolar grains found in all unaltered primitive meteorites, though more localized heating events undoubtedly occurred. Fine-grained, crystalline silicates in comets, meteorites and IDPs are therefore products of relatively localized thermal and/or aqueous processes and their presence can potentially be used to constrain the metamorphic events that occurred both in the nebula prior to the formation of primitive planetesimals as well as during subsequent parent body processing. As examples, the presence of crystalline magnesium silicates in comets requires both grain annealing and transport out to the nebular environment where comets form (50-200 AU), whereas in primitive chondrite matrices, crystalline Mg-silicates probably formed by evaporation, recondensation and annealing in the inner nebula. Nevertheless, the presence in both IDPs and chondrite matrices of Mn-rich forsterite and enstatite grains with structures indicative of cooling in days shows that identical thermal processes formed some magnesium silicates in comets and asteroids. The bulk of the amorphous material in primitive chondrite matrices may have formed by evaporation and condensation during high temperature chondrule-forming events. Crystalline FeO-rich silicates, such as olivine and phyllosilicates, formed by secondary processes such as thermal metamorphism and aqueous alteration on asteroidal parent bodies and are not the products of primary nebular processes. We explore several such processes and their wider implications for the chemistry of protostellar systems in this chapter.