scholarly journals Formation of aqua planets with water of nebular origin: effects of water enrichment on the structure and mass of captured atmospheres of terrestrial planets

2020 ◽  
Vol 496 (3) ◽  
pp. 3755-3766 ◽  
Author(s):  
Tadahiro Kimura ◽  
Masahiro Ikoma
Keyword(s):  
Terrestrial Planets ◽  
Magma Ocean ◽  
Solar Abundance ◽  
Produce Water ◽  
Solar Abundances ◽  
Subsequent Loss ◽  
M Dwarf ◽  
Water Amount ◽  
Water Contents ◽  
Made In

ABSTRACT Recent detection of exoplanets with Earth-like insolation attracts growing interest in how common Earth-like aqua planets are beyond the Solar system. While terrestrial planets are often assumed to capture icy or water-rich planetesimals, a primordial atmosphere of nebular origin itself can produce water through oxidation of the atmospheric hydrogen with oxidizing minerals from incoming planetesimals or the magma ocean. Thermodynamically, normal oxygen buffers produce water comparable in mole number equal to or more than hydrogen. Thus, the primordial atmosphere would likely be highly enriched with water vapour; however, the primordial atmospheres have been always assumed to have the solar abundances. Here we integrate the 1D structure of such an enriched atmosphere of sub-Earths embedded in a protoplanetary disc around an M dwarf of 0.3$\, \mathrm{M}_\odot$ and investigate the effects of water enrichment on the atmospheric properties with focus on water amount. We find that the well-mixed highly enriched atmosphere is more massive by a few orders of magnitude than the solar-abundance atmosphere, and that even a Mars-mass planet can obtain water comparable to the present Earth’s oceans. Although close-in Mars-mass planets likely lose the captured water via disc dispersal and photoevaporation, these results suggest that there are more sub-Earths with Earth-like water contents than previously predicted. How much water terrestrial planets really obtain and retain against subsequent loss, however, depends on efficiencies of water production, mixing in the atmosphere and magma ocean, and photoevaporation, detailed investigation for which should be made in the future.

Steam Atmospheres and Magma Oceans on Planets

2020 ◽  
Author(s):  
Keiko Hamano
Keyword(s):  
Feedback Loop ◽  
Radiative Energy ◽  
Terrestrial Planets ◽  
Magma Ocean ◽  
Planetary Body ◽  
Oxidation Of H2 ◽  
Giant Impacts ◽  
Magma Oceans ◽  
Greenhouse Effects ◽  
Insight Into

A magma ocean is a global layer of partially or fully molten rocks. Significant melting of terrestrial planets likely occurs due to heat release during planetary accretion, such as decay heat of short-lived radionuclides, impact energy released by continuous planetesimal accretion, and energetic impacts among planetary-sized bodies (giant impacts). Over a magma ocean, all water, which is released upon impact or degassed from the interior, exists as superheated vapor, forming a water-dominated, steam atmosphere. A magma ocean extending to the surface is expected to interact with the overlying steam atmosphere through material and heat exchange. Impact degassing of water starts when the size of a planetary body becomes larger than Earth’s moon or Mars. The degassed water could build up and form a steam atmosphere on protoplanets growing by planetesimal accretion. The atmosphere has a role in preventing accretion energy supplied by planetesimals from escaping, leading to the formation of a magma ocean. Once a magma ocean forms, part of the steam atmosphere would start to dissolve into the surface magma due to the high solubility of water into silicate melt. Theoretical studies indicated that as long as the magma ocean is present, a negative feedback loop can operate to regulate the amount of the steam atmosphere and to stabilize the surface temperature so that a radiative energy balance is achieved. Protoplanets can also accrete the surrounding H2-rich disk gas. Water could be produced by oxidation of H2 by ferrous iron in the magma. The atmosphere and water on protoplanets could be a mixture of outgassed and disk-gas components. Planets formed by giant impact would experience a global melting on a short timescale. A steam atmosphere could grow by later outgassing from the interior. Its thermal blanketing and greenhouse effects are of great importance in controlling the cooling rate of the magma ocean. Due to the presence of a runaway greenhouse threshold, the crystallization timescale and water budget of terrestrial planets can depend on the orbital distance from the host star. The terrestrial planets in our solar system essentially have no direct record of their earliest history, whereas observations of young terrestrial exoplanets may provide us some insight into what early terrestrial planets and their atmosphere are like. Evolution of protoplanets in the framework of pebble accretion remains unexplored.

Implications of magma oceans for astrophysical observations: mass-radius and atmospheric composition

2020 ◽  
Author(s):  
Dan J. Bower ◽  
Daniel Kitzmann ◽  
Aaron Wolf ◽  
Patrick Sanan ◽  
Caroline Dorn ◽  
...  
Keyword(s):  
Building Blocks ◽  
Atmospheric Composition ◽  
Terrestrial Planets ◽  
Iron Core ◽  
Magma Ocean ◽  
Static Structure ◽  
Emission Data ◽  
Modelling Framework ◽  
Magma Oceans ◽  
Structure Calculations

<div> <div> <div> <p>The earliest secondary atmosphere of a rocky planet originates from extensive volatile release during one or more magma ocean epochs that occur during and after the assembly of the planet. Magma oceans set the stage for the long-term evolution of terrestrial planets by establishing the major chemical reservoirs of the iron core and silicate mantle, chemical stratification within the mantle, and outgassed atmosphere. Furthermore, current and future exoplanet observations will favour the detection and characterisation of hot and warm planets, potentially with large outgassed atmospheres. In this study, we highlight the potential to combine models of coupled interior–atmosphere evolution with static structure calculations and modelled atmospheric spectra (transmission and emission). By combining these components in a common modelling framework, we acknowledge planets as dynamic entities and leverage their evolution to bridge planet formation, interior-atmosphere interaction, and observations.</p> <p>An interior–atmosphere model is combined with static structure calculations to track the evolving radius of a hot rocky mantle that is outgassing volatiles. We consider oxidised species CO2 and H2O and generate synthetic emission and transmission spectra for CO2 and H2O dominated atmospheres. Atmospheres dominated by CO2 suppress the outgassing of H2O to a greater extent than previously realised, since previous studies have applied an erroneous relationship between volatile mass and partial pressure. Furthermore, formation of a lid at the surface can tie the outgassing of H2O to the efficiency of heat transport through the lid, rather than the radiative timescale of the atmosphere. We extend this work to explore the speciation of a primary atmosphere that is constrained using meteoritic materials as proxies for the planetary building blocks, and find that a range of reducing and oxidising atmospheres are possible.</p> </div> </div> </div><div> <div> <div> <p>Our results demonstrate that a hot molten planet can have a radius several percent larger (about 5%, assuming Earth-like core size) than its equivalent solid counterpart, which may explain the larger radii of some close-in exoplanets. Outgassing of a low molar mass species (such as H2O, compared to CO2) can combat the continual contraction of a planetary mantle and even marginally increase the planetary radius. We further use our models to generate synthetic transmission and emission data to aid in the detection and characterisation of rocky planets via transits and secondary eclipses. Atmospheres of terrestrial planets around M-stars that are dominated by CO2 versus H2O could be distinguished by future observing facilities that have extended wavelength coverage (e.g., JWST). Incomplete magma ocean crystallisation, as may be the case for close-in terrestrial planets, or full or part retention of an early outgassed atmosphere, should be considered in the interpretation of observational data from current and future observing facilities.</p> </div> </div> </div>

scholarly journals Formation of terrestrial planets from planetesimals around M dwarfs

2007 ◽  
Vol 3 (S249) ◽  
pp. 305-308
Author(s):  
Masahiro Ogihara ◽  
Shigeru Ida
Keyword(s):  
Terrestrial Planet ◽  
Terrestrial Planets ◽  
Type I ◽  
M Dwarfs ◽  
Mean Motion Resonances ◽  
Mean Motion ◽  
Habitable Zones ◽  
Pile Up ◽  
Solar Type ◽  
Water Contents

AbstractWe have investigated accretion of terrestrial planets from planetesimals around M dwarfs through N-body simulations including the effect of tidal interaction with disk gas. Because of low luminosity of M dwarfs, habitable zones around them are located near the disk inner edge. Planetary embryos undergo type-I migration and pile up near the disk inner edge. We found that after repeated close scatterings and occasional collisions, three or four planets eventually remain in stable orbits in their mean motion resonances. Furthermore, large amount of water-rich planetesimals rapidly migrate to the terrestrial planet regions from outside of the snow line, so that formed planets in these regions have much more water contents than those around solar-type stars.

scholarly journals Physical properties of terrestrial planets and water delivery in the habitable zone using N-body simulations with fragmentation

2019 ◽  
Vol 632 ◽  
pp. A14 ◽  
Author(s):  
A. Dugaro ◽  
G. C. de Elía ◽  
L. A. Darriba
Keyword(s):  
Terrestrial Planets ◽  
Habitable Zone ◽  
Water Delivery ◽  
Class A ◽  
Class B ◽  
Solar Type ◽  
Formation And Evolution ◽  
Final Fraction ◽  
The Masses ◽  
Water Contents

Aims. The goal of this research is to study how the fragmentation of planetary embryos can affect the physical and dynamical properties of terrestrial planets around solar-type stars. Our study focuses on the formation and evolution of planets and water delivery in the habitable zone (HZ). We distinguish class A and class B HZ planets, which have an accretion seed initially located inside and beyond the snow line, respectively. Methods. We developed an N-body integrator that incorporates fragmentation and hit-and-run collisions, which is called D3 N-body code. From this, we performed 46 numerical simulations of planetary accretion in systems that host two gaseous giants similar to Jupiter and Saturn. We compared two sets of 23 N-body simulations, one of which includes a realistic collisional treatment and the other one models all impacts as perfect mergers. Results. The final masses of the HZ planets formed in runs with fragmentation are about 15–20% lower than those obtained without fragmentation. As for the class A HZ planets, those formed in simulations without fragmentation experience very significant increases in mass with respect to their initial values, while the growth of those produced in runs with fragmentation is less relevant. We remark that the fragments play a secondary role in the masses of the class A HZ planets, providing less than 30% of their final values. In runs without fragmentation, the final fraction of water of the class A HZ planets keeps the initial value since they do not accrete water-rich embryos. In runs with fragmentation, the final fraction of water of such planets strongly depends on the model used to distribute the water after each collision. The class B HZ planets do not show significant differences concerning their final water contents in runs with and without fragmentation. From this, we find that the collisional fragmentation is not a barrier to the survival of water worlds in the HZ.

A re-examination of water in agate and its bearing on the agate genesis enigma

2017 ◽  
Vol 81 (5) ◽  
pp. 1223-1244 ◽  
Author(s):  
Terry Moxon
Keyword(s):  
High Temperature ◽  
Molecular Water ◽  
Water Vapour Pressure ◽  
Total Water ◽  
Powder Preparation ◽  
Water Losses ◽  
Produce Water ◽  
High Temperature Furnace ◽  
Temperature Heating ◽  
Water Contents

AbstractDehydration of silanol and molecular water in 60 agates from 12 hosts with ages between 23 to 2717 Ma has been investigated using desiccators and high-temperature furnace heating. There are wide differences in the water data obtained under uncontrolled and fixed atmospheric water vapour pressure conditions. After agate acclimatization at 20°C and 46% relative humidity, the total water (silanol and molecular) was determined in powders and mini-cuboids by heating samples at 1200°C. Agates from hosts < 180 Ma all showed a greater mass loss using powders and demonstrate that after prolonged high-temperature heating, silanol water is partially-retained by the mini-cuboids. Desiccator dehydration of powders and slabs shows that powder preparation can produce water losses; this is particularly relevant in agates from hosts < 180 Ma. The identified problems have consequences for water quantification in agate and chalcedony using infrared or thermogravimetric techniques. Mobile and total water in agate is considered in relation to host-rock age, mogánite content and crystallite size. Links are observed between the various identified water contents allowing comment on quartz development and agate genesis. The water data also supports previous claims that agates from New Zealand and Brazil were formed long after their host.

Compositions of chondrites

1988 ◽  
Vol 325 (1587) ◽  
pp. 535-544 ◽  
Keyword(s):  
Boundary Conditions ◽  
Physical Properties ◽  
Solar Nebula ◽  
Terrestrial Planets ◽  
Volatile Elements ◽  
High Loss ◽  
Innermost Part ◽  
Solar Abundances

A compilation of data on 78 elements in the nine groups of chondrites shows each to be isochemical with the exception of a few volatiles. With the exception of the most volatile elements, the groups have solar abundances to within a factor of two. The solar abundances and the chemical and physical properties of phases in the leastaltered chondrites indicate formation by grain agglomeration in the preplanetary nebula. Planets formed by the gradual growth of bodies in the solar nebula. Because there is no evidence for the formation of non-chondritic bodies in the nebula, the simplest model calls for the bulk compositions of the terrestrial planets to be chondritic. Mercury is enriched in metal, perhaps either because of high loss of silicates due to enhanced radial drag in the innermost part of the nebula, or because of enhanced accretion of metallic cores from disrupted asteroids. Chondritic compositions should be considered as boundary conditions for planetary models.

A new theory on Mercury's origin

2020 ◽  
Author(s):  
Manuel Scherf ◽  
Nikolay Erkaev ◽  
Helmut Lammer
Keyword(s):  
Solar Nebula ◽  
Surface Composition ◽  
Building Blocks ◽  
The Body ◽  
Terrestrial Planets ◽  
Magma Ocean ◽  
Volatile Elements ◽  
Continuous Growth ◽  
Giant Impact ◽  
First Time

&lt;p&gt;Of all the terrestrial planets in the Solar System Mercury stands out with a remarkably high core-mantle ratio, with its core occupying about 85% of the planetary radius. Several different theories tried to explain its high Fe/Si-ratio; the giant impact theory (e.g. [1]) for instance argues that one or more giant impacts stripped away most of the Hermean mantle, while the core remained and formed the smallest of the terrestrial planets. Another theory explains the high density of Mercury through a partial volatilization during the time of the solar nebula (e.g. [2]). Here, proto-Mercury is assumed to be substantially more massive than at present-day with a composition close to those of the other terrestrial planets. When the planet was surrounded by the hot solar nebula, however, most of the mantle evaporated, ending up with present-day Mercury. Other theories argue with the particular primordial conditions of its orbital location that might have favored the accretion of dense and volatile poor building-blocks such as enstatite chondrites (e.g. [3,4]). Messenger, however, revealed a surface composition that is surprisingly rich in volatile and moderately volatile elements [4]. This is hardly compatible with the giant impact and vaporization theory but supports hypothesis that connect Mercury&amp;#8217;s high core-mantle ratio to the particular conditions of its orbital location.&lt;/p&gt; &lt;p&gt;Within this talk, we will for the first time present a new model that connects these conditions with accretion and partial planetary evaporation. We will argue that Mercury (in contrast to old evaporation theories) was released out of the nebula as a small planetary embryo, comparable in size to the moon, that was covered with a global magma ocean. While the embryo proceeds to grow through frequent impactors, (moderately) volatile elements evaporate from the magma ocean and are lost into space due to the high surface temperature, the low gravity of the body and the high XUV flux from the young Sun. Here, lighter and more volatile elements are preferentially lost from the embryo, while the heavier and less volatile elements escape less efficient. Due to the continuous growth of proto-Mercury, however, the gravitational energy will start to dominate over the thermal energy of the evaporated particles, making them harder and harder to escape, which ultimately halts the loss of moderately volatile elements. Mercury subsequently finalizes its accretion with relatively volatile rich material and evolves to the body we can observe at present-day. We simulated the escape of (moderately) volatile elements with an adopted version of a 1D hydrodynamic upper atmosphere model (e.g. [5]) and will present our results here for the first time.&lt;/p&gt; &lt;p&gt;&lt;strong&gt;References:&lt;/strong&gt; [1] Benz, W. et al., Space Sciences Series of ISSI, Volume 26, p. 7., 2008. [2] Cameron, A.G.W., Icarus, Volume 64, Issue 2, p. 285-294., 1985. [3] Charlier, B. and Namur, O., Elements, Volume 15, p. 9-14, 2019. [4] Nittler, Larry R. et al., Science, Volume 333, Issue 6051, pp. 1847, 2011. []5 Erkaev, et al., MNRAS, Volume 460, Issue 2, p.1300-1309, 2016.&lt;/p&gt;

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