The abundance of<sup>26</sup>Al-rich planetary systems in the Galaxy

Gounelle, M.

doi:10.1051/0004-6361/201526174

Cited by 47 publications

(43 citation statements)

References 83 publications

(98 reference statements)

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“…Melt-water then oxidizes the rocks, and H 2 returns to the nebula (e.g., Young 2001;Rosenberg et al 2001;Monteux et al 2018). Because most protoplanetary disks probably had fewer SLRs than our own Gounelle 2015;Lichtenberg et al 2016;Dwardakas et al 2017; see also Jura et al 2013), this process would operate differently (or not at all) in other planetary systems. Another explanation for the dryness of carbonaceous chondrites relies on Jupiter's early formation ; gas giants of Jupiter's size and semimajor axis are not typical.…”

Section: Volatile-tracking Modelmentioning

confidence: 92%

Habitability of Exoplanet Waterworlds

Kite

Ford

2018

ApJ

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Many habitable zone (HZ) exoplanets are expected to form with water mass fractions higher than that of the Earth. For rocky exoplanets with 10-1000× Earth's H 2 O but without H 2 , we model the multi-Gyr evolution of ocean temperature and chemistry, taking into account C partitioning, high-pressure ice phases, and atmosphere-lithosphere exchange. Within our model, for Sun-like stars, we find that:(1) the duration of habitable surface water is strongly affected by ocean chemistry; (2) possible ocean pH spans a wide range; (3) surprisingly, many waterworlds retain habitable surface water for >1 Gyr, and (contrary to previous claims) this longevity does not necessarily involve geochemical cycling.The key to this cycle-independent planetary habitability is that C exchange between the convecting mantle and the water ocean is curtailed by seafloor pressure on waterworlds, so the planet is stuck with the ocean mass and ocean cations that it acquires during the first 1% of its history. In our model, the sum of positive charges leached from the planetary crust by early water-rock interactions is -coincidentally -often within an order of magnitude of the early-acquired atmosphere+ocean inorganic C inventory overlaps. As a result, p CO2 is frequently in the "sweet spot" (0.2-20 bar) for which the range of semimajor axis that permits surface liquid water is about as wide as it can be. Because the width of the HZ in semimajor axis defines (for Sun-like stars) the maximum possible time span of surface habitability, this effect allows for Gyr of habitability as the star brightens. We illustrate our findings by using the output of an ensemble of N -body simulations as input to our waterworld evolution code. Thus (for the first time in an end-to-end calculation) we show that chance variation of initial conditions, with no need for geochemical cycling, can yield multi-Gyr surface habitability on waterworlds.

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Section: Volatile-tracking Modelmentioning

confidence: 92%

Habitability of Exoplanet Waterworlds

Kite

Ford

2018

ApJ

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“…There has been much speculation on the possibility of other ionization sources close to the mid-plane. In addition to stellar and galactic cosmic rays, locally-generated energetic particles may generate sufficient ionization to reduce the amount of MRI-dead material (e.g., Turner & Drake 2009; see also Gounelle 2015 for the role of radioactive nuclides and Ilgner & Nelson 2008 for the potential role of mixing). MRI turbulence itself may play a role here, as discussed recently by Inutsuka & Sano (2005) and Okuzumi & Inutsuka (2015).…”

Section: Application To Magnetic Disksmentioning

confidence: 99%

Deep-down ionization of protoplanetary discs

Glassgold

Lizano²,

Galli

2017

Monthly Notices of the Royal Astronomical Society

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The possible occurrence of dead zones in protoplanetary disks subject to the magnetorotational instability highlights the importance of disk ionization. We present a closedform theory for the deep-down ionization by X-rays at depths below the disk surface dominated by far-ultraviolet radiation. Simple analytic solutions are given for the major ion classes, electrons, atomic ions, molecular ions and negatively charged grains. In addition to the formation of molecular ions by X-ray ionization of H 2 and their destruction by dissociative recombination, several key processes that operate in this region are included, e.g., charge exchange of molecular ions and neutral atoms and destruction of ions by grains. Over much of the inner disk, the vertical decrease in ionization with depth into the disk is described by simple power laws, which can easily be included in more detailed modeling of magnetized disks. The new ionization theory is used to illustrate the non-ideal MHD effects of Ohmic, Hall and Ambipolar diffusion for a magnetic model of a T Tauri star disk using the appropriate Elsasser numbers.

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“…Assuming the 26 Al abundance inferred for the early solar system from the analysis of meteorites (McPherson et al 1995;Umebayashi & Nakano 2009), SLRs can maintain an ionisation rate of ≈ 10 −19 s −1 in the mid-plane of a disc for ≈ 1 Myr, while LLRs lead to ionisation rates of only ≈ 10 −22 s −1 , but on timescales much longer than the disc lifetimes (Umebayashi & Nakano 2009;Cleeves et al 2013). However, since the average Galactic abundance of 26 Al inferred from its γ-ray emission is about one order of magnitude lower than the meteoritic solar system value (Diehl et al 2006), the probability for a star of being born in a 26 Al-rich environment, as in the case of the Sun, is relatively low (Gounelle 2015).…”

Section: Introductionmentioning

confidence: 97%

Cosmic-ray ionisation in circumstellar discs

Padovani

Ivlev

Galli

et al. 2018

A&A

157

268

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Context. Galactic cosmic rays (CRs) are a ubiquitous source of ionisation of the interstellar gas, competing with UV and X-ray photons as well as natural radioactivity in determining the fractional abundance of electrons, ions, and charged dust grains in molecular clouds and circumstellar discs. Aims. We model the propagation of various components of Galactic CRs versus the column density of the gas. Our study is focussed on the propagation at high densities, above a few g cm −2 , especially relevant for the inner regions of collapsing clouds and circumstellar discs.Methods. The propagation of primary and secondary CR particles (protons and heavier nuclei, electrons, positrons, and photons) is computed in the continuous slowing down approximation, diffusion approximation, or catastrophic approximation by adopting a matching procedure for the various transport regimes. A choice of the proper regime depends on the nature of the dominant loss process modelled as continuous or catastrophic. Results. The CR ionisation rate is determined by CR protons and their secondary electrons below ≈ 130 g cm −2 and by electronpositron pairs created by photon decay above ≈ 600 g cm −2 . We show that a proper description of the particle transport is essential to compute the ionisation rate in the latter case, since the electron and positron differential fluxes depend sensitively on the fluxes of both protons and photons. Conclusions. Our results show that the CR ionisation rate in high-density environments, such as the inner parts of collapsing molecular clouds or the mid-plane of circumstellar discs, is higher than previously assumed. It does not decline exponentially with increasing column density, but follows a more complex behaviour because of the interplay of the different processes governing the generation and propagation of secondary particles.

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The abundance of²⁶Al-rich planetary systems in the Galaxy

Cited by 47 publications

References 83 publications

Habitability of Exoplanet Waterworlds

Habitability of Exoplanet Waterworlds

Deep-down ionization of protoplanetary discs

Cosmic-ray ionisation in circumstellar discs

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The abundance of26Al-rich planetary systems in the Galaxy

Cited by 47 publications

References 83 publications

Habitability of Exoplanet Waterworlds

Habitability of Exoplanet Waterworlds

Deep-down ionization of protoplanetary discs

Cosmic-ray ionisation in circumstellar discs

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Product

Resources

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The abundance of²⁶Al-rich planetary systems in the Galaxy