Origins, Worlds, and Life A Decadal Strategy for Planetary Science and Astrobiology 2023-2032 (2023) / Chapter Skim
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4 Question 1: Evolution of the Protoplanetary Disk
4 Question 1: Evolution of the Protoplanetary Disk
Pages 101-126
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From page 101... ...
This chapter addresses the history of the solar nebula, the protoplanetary disk that evolved into the solar system.1 Our disk was formed as a by-product of star formation via the collapse of a molecular cloud composed of gas and dust. The evolution of the protoplanetary disk had four sequential, but partially contemporaneous phases: (1)
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From page 102... ...
Q1.1 WHAT WERE THE INITIAL CONDITIONS IN THE SOLAR SYSTEM? The story of the protoplanetary disk is one of rapid evolution occurring as new material infalls from the stellar birth cluster and is transported and processed within the disk.
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From page 103... ...
These data demonstrate that the molecular cloud core was not fully homogenized or had not digested its inherited interstellar components (Nittler and Ciesla 2016) , and that laboratory measurements of minute isotopically anomalous materials can be used to investigate the molecular cloud collapse, inherited protosolar components, and disk evolution.
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From page 104... ...
If the collapse of the molecular cloud that made the Sun was triggered by a stellar explosion, the nature and distribution of presolar materials and extinct radionuclides could have been heterogeneous between the inner and outer parts of the solar system. The analysis of extinct radioactivity products and of presolar phases requires, however, analytical precision and spatial resolution that cannot be obtained in situ on planetary objects through missions.
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From page 105... ...
Chondritic meteorites (EC, enstatite chondrite; OC, ordinary chondrites; CC, carbonaceous chondrites, with subgroups CI, CM, CB, and CR) are shown in approximate relative distance from the Sun of each parent body.
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From page 106... ...
Testing the heterogeneity and dynamics of molecular cloud core contributions, including refractory dust and more easily altered organic matter, would require return of material originating from the outer solar system to terrestrial laboratories or definitive proof that a primitive sample originated in that region. Heterogeneous infall of stellar material alone cannot produce all of the observed isotopic variability.
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From page 107... ...
(a) In the initial stages of the molecular cloud core collapse, (1)
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From page 108... ...
• Address the timing and role of injection of supernova material on the formation of the solar nebula, and distinguish materials that retain a presolar heritage from the products of nebular and parent body processes through return of comet samples and laboratory isotopic analyses of returned and terrestrially collected samples. • Constrain the role of self-shielding on the formation of O and N isotopic reservoirs in the solar nebula through spatially resolved astronomical observations of isotopologues C- and O-bearing species in protoplanetary disks and the interstellar medium using ground- and space-based telescopes (e.g., ALMA and the James Webb Space Telescope)
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From page 109... ...
It is unclear how much of the diversity in the organic matter observed across chondrites and cometary dust samples is owing to differences in hydrothermal parent body processing and how much reflects differences in the materials accreted to different parent bodies. Moreover, the range of formation locations, temperatures, and mechanisms spans accretion as icy mantles on anhydrous minerals in the outer nebula, accretion to metal grains and chondrules in the inner nebula, and as direct nebular condensates (Alexander et al.
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From page 110... ...
Such substructures may have formed as the result of these disk transport mechanisms or alternatively by the accretion of giant planets, and whether planets or substructures came first is unclear. In either case, the formation of substructures themselves would have then influenced subsequent disk evolution, possibly serving as a barrier to further transport in their locations or instead filtering the grain sizes of transported materials.
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From page 111... ...
Third, despite astronomical evidence for the presence of holes, rings, and gaps in other protoplanetary disks, it is unknown whether the solar nebula formed such substructures. Accepting that it did, their geometry, location, and timing are critical to understanding planet formation processes, as are the mechanisms that influenced their formation.
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From page 112... ...
• Determine if, how, when, and where gaps, rings, or holes developed in the nebular disk through spacecraft isotopic and elemental measurements of gas, dust, ice, and organic components in outer and inner solar bodies; return of asteroid and comet surface samples; disk transport modeling; ground- and space-based astronomical measurements of protoplanetary disks; and laboratory petrologic, isotopic, and paleomagnetic analyses of returned and terrestrially collected samples. • Constrain the original compositions and processing histories of dust, gas, ice, and organic matter in the solar nebula through return of asteroid and comet surface samples; astronomical observations of young stellar objects and outer solar system volatiles; modeling of heating and radiation processing; and laboratory petrographic, elemental, and isotopic analyses of returned and terrestrially collected asteroid and comet samples.
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From page 113... ...
. Furthermore, observations of protoplanetary disks by ALMA and the next-generation Very Large Array can provide constraints on the growth of up to centimeter-scale particles.
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From page 114... ...
2008) and pressure bumps (e.g., associated with volatile snow lines, forming giant planets, and a variety of hydrodynamic or magnetohydrodynamic instabilities [Johansen et al.
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From page 115... ...
New observations of primitive bodies and sample return mission that clarify genetic relationships between meteorite and IDPs already in our collections and specific bodies would be particularly valuable. In the case of Jupiter, the Galileo probe found that the most volatile elements (e.g., noble gases and nitrogen)
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From page 116... ...
Determining the elemental enrichments in the atmospheres of the other giant planets is key to generalizing and discriminating between different scenarios of disk conditions and evolution that led to giant planet formation. The noble gases are particularly useful in this respect (see Q2.2)
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From page 117... ...
• Test models of accretion of micrometer-to-centimeter-scale objects by determining the relative ages of crystallization of chondrules, CAIs, and mineral grains, and thermal and aqueous alteration events using return of comet surface samples; and laboratory radioisotopic analyses of returned surface samples from comets and asteroids and terrestrially collected samples. • Constrain accretion processes in protoplanetary disks by resolved studies of the volatile composition as well as of the composition, sizes and shapes of grains using ground- and space-based telescopic observations of protoplanetary disks.
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From page 118... ...
through limited direct and indirect evidence. Astronomical observations of the abundance of dust and gas and of active accretion onto protostars indicate that protoplanetary disks have estimated lifetimes from <1 to ~20 million years with a mean value of FIGURE 4-4 Meteorite constraints on the lifetime of the nebula and its magnetic field.
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From page 119... ...
The role of magnetized disk winds versus photoevaporation could be constrained by paleomagnetic measurements of meteorites, as discussed here. Also, constraints on the gas density as a function of time and distance from the Sun and young stellar objects using meteorite studies and astronomical observations could determine the direction of dispersal (inward, outward, or with gaps)
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From page 120... ...
• Measure the intensity of the solar nebula magnetic field as a function of space and time with return of asteroid and comet surface samples; in situ magnetic measurements at asteroids, comets, Centaurs, and Kuiper belt objects; and laboratory paleomagnetic measurements of returned and terrestrially collected samples. • Measure the temporal and spatial evolution of the density, composition, and magnetism of protoplanetary disks using optical, infrared, millimeter, and radio measurements of nearby young stellar objects.
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From page 121... ...
428–436 in Chondrules: Records of Protoplanetary Disk Processes. Cambridge Planetary Sciences, S
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From page 122... ...
Late Formation in a Chemically Evolved Protosolar Disc." Monthly Notices of the Royal Astronomical Society 367:L47–L51. Heays, A.N., R
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From page 123... ...
2004. "Chondrule Formation and Protoplanetary Disk Heating by Current Sheets in Nonideal Magnetohydrodynamic Turbulence." Astrophysical Journal 606:532–541.
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From page 124... ...
2018. "The Reten tion of Dust in Protoplanetary Disks: Evidence from Agglomeratic Olivine Chondrules from the Outer Solar System." Geochimica et Cosmochimica Acta 223:405–421.
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From page 125... ...
2005. "Streaming Instabilities in Protoplanetary Disks." Astrophysical Journal 620:459–469.
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From page 126... ...
Q2 PLATE: An enhanced-color image mosaic of Pluto and Charon taken by the New Horizons spacecraft in 2015. SOURCE: Courtesy of NASA/JHUAPL/SwRI.
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