Evidence for molecular cloud material in meteorites and interplanetary dust

The short-lived 26Al radionuclide is thought to have been admixed into the initially 26Al-poor protosolar molecular cloud before or contemporaneously with its collapse. Bulk inner Solar System reservoirs record positively correlated variability in mass-independent 54Cr and 26Mg*, the decay product of 26Al. This correlation is interpreted as reflecting progressive thermal processing of in-falling 26Al-rich molecular cloud material in the inner Solar System. The thermally unprocessed molecular cloud matter reflecting the nucleosynthetic makeup of the molecular cloud before the last addition of stellar-derived 26Al has not been identified yet but may be preserved in planetesimals that accreted in the outer Solar System. We show that metal-rich carbonaceous chondrites and their components have a unique isotopic signature extending from an inner Solar System composition toward a 26Mg*-depleted and 54Cr-enriched component. This composition is consistent with that expected for thermally unprocessed primordial molecular cloud material before its pollution by stellar-derived 26Al. The 26Mg* and 54Cr compositions of bulk metal-rich chondrites require significant amounts (25–50%) of primordial molecular cloud matter in their precursor material. Given that such high fractions of primordial molecular cloud material are expected to survive only in the outer Solar System, we infer that, similarly to cometary bodies, metal-rich carbonaceous chondrites are samples of planetesimals that accreted beyond the orbits of the gas giants. The lack of evidence for this material in other chondrite groups requires isolation from the outer Solar System, possibly by the opening of disk gaps from the early formation of gas giants.

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Building protoplanetary disks from the molecular cloud: redefining the disk timeline

Astronomy and Astrophysics ◽

10.1051/0004-6361/201730677 ◽

2019 ◽

Vol 624 ◽

pp. A93 ◽

Cited By ~ 2

Author(s):

K. Baillié ◽

J. Marques ◽

L. Piau

Keyword(s):

Molecular Cloud ◽

Protoplanetary Disk ◽

Giant Planets ◽

Type I ◽

Initial State ◽

Disk Formation ◽

Heat Transition ◽

Cloud Material ◽

Selection Of ◽

Collapse Phase

Context. Planetary formation models are necessary to understand the characteristics of the planets that are the most likely to survive. Their dynamics, their composition and even the probability of their survival depend on the environment in which they form. We therefore investigate the most favorable locations for planetary embryos to accumulate in the protoplanetary disk: the planet traps. Aims. We study the formation of the protoplanetary disk by the collapse of a primordial molecular cloud, and how its evolution leads to the selection of specific types of planets. Methods. We use a hydrodynamical code that accounts for the dynamics, thermodynamics, geometry and composition of the disk to numerically model its evolution as it is fed by the infalling cloud material. As the mass accretion rate of the disk onto the star determines its growth, we can calculate the stellar characteristics by interpolating its radius, luminosity and temperature over the stellar mass from pre-calculated stellar evolution models. The density and midplane temperature of the disk then allow us to model the interactions between the disk and potential planets and determine their migration. Results. At the end of the collapse phase, when the disk reaches its maximum mass, it pursues its viscous spreading, similarly to the evolution from a minimum mass solar nebula (MMSN). In addition, we establish a timeline equivalence between the MMSN and a “collapse-formed disk” that would be older by about 2 Myr. Conclusions. We can save various types of planets from a fatal type-I inward migration: in particular, planetary embryos can avoid falling on the star by becoming trapped at the heat transition barriers and at most sublimation lines (except the silicates one). One of the novelties concerns the possible trapping of putative giant planets around a few astronomical units from the star around the end of the infall. Moreover, trapped planets may still follow the traps outward during the collapse phase and inward after it. Finally, this protoplanetary disk formation model shows the early possibilities of trapping planetary embryos at disk stages that are anterior by a few million years to the initial state of the MMSN approximation.

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Ices in star forming regions

Symposium - International Astronomical Union ◽

10.1017/s0074180900009232 ◽

1997 ◽

Vol 178 ◽

pp. 45-60 ◽

Cited By ~ 11

Author(s):

A.G.G.M. Tielens ◽

D.C.B. Whittet

Keyword(s):

Ir Spectra ◽

Gas Phase ◽

Molecular Cloud ◽

Oxidation Reactions ◽

Star Forming ◽

Star Forming Regions ◽

Interstellar Ice ◽

Simple Molecules ◽

Absorption Features ◽

Cloud Material

IR spectra of sources associated with molecular cloud material show a variety of absorption features attributed to simple molecules, such as H2O, CO, CH3OH, CO2, CH4, and OCS in icy grain mantles. These identifications are reviewed. These molecules are formed through accretion and reaction of gas phase species on grain surfaces. The high abundance of CH3OH and CO2 point towards the importance of hydrogenation and oxidation reactions in this process. Observations also show that thermal outgassing is of great importance for the composition of interstellar ice mantles. Both these processes are discussed in some detail.

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Multiple generations of grain aggregation in different environments preceded solar system body formation

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1720167115 ◽

2018 ◽

Vol 115 (26) ◽

pp. 6608-6613 ◽

Cited By ~ 10

Author(s):

Hope A. Ishii ◽

John P. Bradley ◽

Hans A. Bechtel ◽

Donald E. Brownlee ◽

Karen C. Bustillo ◽

...

Keyword(s):

Solar System ◽

Organic Carbon ◽

Molecular Cloud ◽

Interstellar Dust ◽

Solar Nebula ◽

Carbon Matrix ◽

Interplanetary Dust ◽

Dust Particles ◽

Interplanetary Dust Particles ◽

System Body

The solar system formed from interstellar dust and gas in a molecular cloud. Astronomical observations show that typical interstellar dust consists of amorphous (a-) silicate and organic carbon. Bona fide physical samples for laboratory studies would yield unprecedented insight about solar system formation, but they were largely destroyed. The most likely repositories of surviving presolar dust are the least altered extraterrestrial materials, interplanetary dust particles (IDPs) with probable cometary origins. Cometary IDPs contain abundant submicrona-silicate grains called GEMS (glass with embedded metal and sulfides), believed to be carbon-free. Some have detectable isotopically anomalousa-silicate components from other stars, proving they are preserved dust inherited from the interstellar medium. However, it is debated whether the majority of GEMS predate the solar system or formed in the solar nebula by condensation of high-temperature (>1,300 K) gas. Here, we map IDP compositions with single nanometer-scale resolution and find that GEMS contain organic carbon. Mapping reveals two generations of grain aggregation, the key process in growth from dust grains to planetesimals, mediated by carbon. GEMS grains, some witha-silicate subgrains mantled by organic carbon, comprise the earliest generation of aggregates. These aggregates (and other grains) are encapsulated in lower-density organic carbon matrix, indicating a second generation of aggregation. Since this organic carbon thermally decomposes above ∼450 K, GEMS cannot have accreted in the hot solar nebula, and formed, instead, in the cold presolar molecular cloud and/or outer protoplanetary disk. We suggest that GEMS are consistent with surviving interstellar dust, condensed in situ, and cycled through multiple molecular clouds.

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The Transition from Diffuse Molecular Gas to Molecular Cloud Material in Taurus

The Astrophysical Journal ◽

10.3847/1538-4357/abf4dd ◽

2021 ◽

Vol 914 (1) ◽

pp. 59

Author(s):

S. R. Federman ◽

Johnathan S. Rice ◽

A. M. Ritchey ◽

Hwihyun Kim ◽

John H. Lacy ◽

...

Keyword(s):

Molecular Cloud ◽

Molecular Gas ◽

Cloud Material

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Interstellar Matter in Meteorites and Interplanetary Dust

Symposium - International Astronomical Union ◽

10.1017/s0074180900165088 ◽

2000 ◽

Vol 197 ◽

pp. 527-536

Author(s):

S. Messenger

Keyword(s):

Molecular Cloud ◽

Interplanetary Dust ◽

Chemical Processes ◽

Dust Particles ◽

Circumstellar Dust ◽

Interstellar Matter ◽

Dust Grains ◽

Interplanetary Dust Particles ◽

Stellar Nucleosynthesis ◽

Isotopic Anomalies

Meteorites and interplanetary dust particles (IDPs) are primitive solar system materials which contain preserved nebular condensates, circumstellar dust grains and partially preserved molecular cloud matter. The circumstellar dust grains found in meteorites are direct samples of a variety of stars, and provide detailed constraints on models of stellar nucleosynthesis. Hydrogen and nitrogen isotopic anomalies in organic matter in meteorites and IDPs are thought to originate from chemical processes in a presolar molecular cloud. This material is better preserved, but less well characterized among IDPs.

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Dynamics of Collapsing Shells

Symposium - International Astronomical Union ◽

10.1017/s0074180900002011 ◽

1996 ◽

Vol 174 ◽

pp. 399-400

Author(s):

Christian Theis

Keyword(s):

Total Energy ◽

Molecular Cloud ◽

Globular Clusters ◽

External Pressure ◽

Hot Gas ◽

Cloud Material

In the last decade several scenarios for the formation of globular clusters have been suggested. One of these models starts with an OB-association exploding near the center of a molecular cloud (Brown et al., ApJ 376, 115 (1991)): The expanding shell sweeps up the cloud material and later the expansion will be decelerated or stopped by the external pressure of the ambient hot gas. The shell itself can break into fragments and form stars. If the total energy of these stars is negative, they will recollapse and eventually form a bound system. According to this idea the dynamics of a thin stellar shell has been studied.

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UV penetrated clumpy molecular cloud cores

Symposium - International Astronomical Union ◽

10.1017/s0074180900198961 ◽

1991 ◽

Vol 147 ◽

pp. 235-244

Author(s):

Jürgen Stutzki ◽

Reinhard Genzel ◽

Urs Graf ◽

Andrew I. Harris ◽

Amiel Sternberg ◽

...

Keyword(s):

Fine Structure ◽

Mass Spectrum ◽

Molecular Cloud ◽

Filling Factor ◽

Large Fraction ◽

Volume Filling ◽

Direct Observations ◽

Cloud Cores ◽

Clump Distribution ◽

Cloud Material

Recent observations of sub-mm and far-IR atomic fine structure and molecular rotational lines give evidence that due to the clumpiness of the molecular cloud cores the UV radiation from newly formed stars affects a very large fraction of the cloud material. Direct observations of the clumpy structure in M17 SW allow to derive several parameters of the clump distribution, in particular the clump mass spectrum and the volume filling factor. Implications of these results in regard to star formation are shortly discussed.

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