scholarly journals Methane hydrate creates the thick oceans in Mimas and Enceladus

2020 ◽  
Author(s):  
Ryusuke Nishitani ◽  
Jun Kimura ◽  
Atsushi Tani ◽  
Sho Sasaki
Keyword(s):  
Heating Rate ◽  
Core Temperature ◽  
Methane Hydrate ◽  
Methane Concentration ◽  
Thermal Evolution ◽  
Internal Heat ◽  
Active Surface ◽  
Hydrate Layer ◽  
Subsurface Ocean ◽  
Tidal Heating

Abstract The difference between the inactive surface of Mimas and the active surface of Enceladus is puzzling. We investigate the conditions under which the both have a thick subsurface ocean and the thermal lithosphere of Mimas is thicker than that of Enceladus by using a one-dimensional simulation of thermal evolution. We adopt the initial core temperature, initial methane concentration, and tidal heating rate as free parameters in the calculation. The initial methane concentration and tidal heating rate greatly affect the current ocean thickness, although the initial core temperature does not affect the thickness. Methane hydrate forms in a subsurface ocean if the initial methane concentration is not 0. The methane hydrate layer plays an insulative role in an icy shell. When the initial methane concentration is 1000 \(\text{m}\text{o}\text{l}\hspace{0.17em}{\text{m}}^{-3}\), ∼3 GW is needed to achieve more than 50 km of the subsurface ocean on Mimas and ∼10 GW is needed to achieve more than 25 km of the subsurface ocean on Enceladus. These values are smaller than those needed for when the initial methane concentration is 0 \(\text{m}\text{o}\text{l}\hspace{0.17em}{\text{m}}^{-3}\). The existence of the methane hydrate layer promotes the survival of the subsurface ocean because it insulates internal heat. In addition, it is found that the surface heat flux is depressed if the methane hydrate layer exists, which is consistent with the unrelaxed craters in Mimas. Methane hydrate may explain the thick oceans in Mimas and Enceladus and the inactive shell of Mimas.

scholarly journals Methane hydrates achieve both thick oceans and thick lithospheres in Enceladus and Mimas

2021 ◽  
Author(s):  
Ryusuke Nishitani ◽  
Jun Kimura ◽  
Atsushi Tani ◽  
Sho Sasaki
Keyword(s):  
Heating Rate ◽  
Core Temperature ◽  
Methane Hydrate ◽  
Methane Concentration ◽  
Thermal Evolution ◽  
Internal Heat ◽  
Active Surface ◽  
Hydrate Layer ◽  
Subsurface Ocean ◽  
Tidal Heating

Abstract The difference between the inactive surface of Mimas and the active surface of Enceladus is puzzling. We investigate the conditions under which both have a thick subsurface ocean and the thermal lithosphere of Mimas is thicker than that of Enceladus by using a one-dimensional simulation of thermal evolution. We adopt the initial core temperature, initial methane concentration, and tidal heating rate as free parameters in the calculation. The initial methane concentration and tidal heating rate greatly affect the current ocean thickness, although the initial core temperature does not affect the thickness. Methane hydrate forms at the base of the icy shell if the initial methane concentration is not 0. The methane hydrate layer plays an insulative role in an icy shell. When the initial methane concentration is 1000 , ∼2 GW is needed to achieve more than 50 km of the subsurface ocean on Mimas and ∼7.5 GW is needed to achieve more than 25 km of the subsurface ocean on Enceladus. These values are smaller than those needed when the initial methane concentration is 0 . The existence of the methane hydrate layer promotes the survival of the subsurface ocean because it insulates internal heat. In addition, it is found that the surface heat flux is depressed if the methane hydrate layer exists, which is consistent with the unrelaxed craters in Mimas. Methane hydrate may explain the thick oceans in Mimas and Enceladus and the inactive shell of Mimas.

scholarly journals The subsurface habitability of small, icy exomoons

2020 ◽  
Vol 636 ◽  
pp. A50
Author(s):  
J. N. K. Y. Tjoa ◽  
M. Mueller ◽  
F. F. S. van der Tak
Keyword(s):  
Solar System ◽  
Liquid Water ◽  
Internal Heat ◽  
Phenomenological Approach ◽  
Habitable Zone ◽  
Melting Depth ◽  
Icy Moons ◽  
Subsurface Ocean ◽  
Tidal Heating ◽  
Ice Shell

Context. Assuming our Solar System as typical, exomoons may outnumber exoplanets. If their habitability fraction is similar, they would thus constitute the largest portion of habitable real estate in the Universe. Icy moons in our Solar System, such as Europa and Enceladus, have already been shown to possess liquid water, a prerequisite for life on Earth. Aims. We intend to investigate under what thermal and orbital circumstances small, icy moons may sustain subsurface oceans and thus be “subsurface habitable”. We pay specific attention to tidal heating, which may keep a moon liquid far beyond the conservative habitable zone. Methods. We made use of a phenomenological approach to tidal heating. We computed the orbit averaged flux from both stellar and planetary (both thermal and reflected stellar) illumination. We then calculated subsurface temperatures depending on illumination and thermal conduction to the surface through the ice shell and an insulating layer of regolith. We adopted a conduction only model, ignoring volcanism and ice shell convection as an outlet for internal heat. In doing so, we determined at which depth, if any, ice melts and a subsurface ocean forms. Results. We find an analytical expression between the moon’s physical and orbital characteristics and the melting depth. Since this expression directly relates icy moon observables to the melting depth, it allows us to swiftly put an upper limit on the melting depth for any given moon. We reproduce the existence of Enceladus’ subsurface ocean; we also find that the two largest moons of Uranus (Titania and Oberon) could well sustain them. Our model predicts that Rhea does not have liquid water. Conclusions. Habitable exomoon environments may be found across an exoplanetary system, largely irrespective of the distance to the host star. Small, icy subsurface habitable moons may exist anywhere beyond the snow line. This may, in future observations, expand the search area for extraterrestrial habitable environments beyond the circumstellar habitable zone.

Thermal evolution of Pluto and implications for surface tectonics and a subsurface ocean

Icarus ◽  
2011 ◽  
Vol 216 (2) ◽  
pp. 426-439 ◽  
Author(s):  
Guillaume Robuchon ◽  
Francis Nimmo
Keyword(s):  
Thermal Evolution ◽  
Subsurface Ocean

Interior heating and outgassing of Proxima Cen b: Identification of critical parameters

2021 ◽  
Author(s):  
Lena Noack ◽  
Kristina Kislyakova ◽  
Colin Johnstone ◽  
Manuel Güdel ◽  
Luca Fossati
Keyword(s):  
Magnetic Field ◽  
Induction Heating ◽  
Initial Conditions ◽  
Thermal Evolution ◽  
Rotation Period ◽  
Critical Parameters ◽  
Stellar Spectrum ◽  
Orbital Inclination ◽  
The Past ◽  
Tidal Heating

<p>Since the discovery of a potentially low-mass exoplanet around our nearest neighbour star Proxima Centauri, several works have investigated the likelihood of a shielding atmosphere and therefore the potential surface habitability of Proxima Cen b. However, outgassing processes are influenced by several different (unknown) factors such as the actual planet mass, mantle and core composition, and different heating mechanisms in the interior.<br>We aim to identify the critical parameters that influence the mantle and surface evolution of the planet over time, as well as to potentially constrain the time-dependent input of volatiles from mantle into the atmosphere.</p><p><br>To study the coupled star-planet evolution, we analyse the heating produced in the interior of Proxima Cen b due to induction heating, which strongly varies with both depth and latitude. We calculate different rotation evolutionary tracks for Proxima Centauri and investigate the change in its rotation period and magnetic field strength. Unlike the Sun, Proxima Centauri possesses a very strong magnetic field of at least a few hundred Gauss, which was likely higher in the past. <br>We apply an interior structure model for varying planet masses (derived from the unknown inclination of observation of the Proxima Centauri system) and iron weight fractions, i.e. different core sizes, in the range of observed Fe-Mg variations in the stellar spectrum. <br>We use a mantle convection model to study the thermal evolution and outgassing efficiency of Proxima Cen b. For unknown planetary parameters such as initial conditions we chose randomly selected values. We take into account heating in the interior due to variable radioactive heat sources and latitute- and radius-dependent induction heating, and compare the heating efficiency to tidal heating.</p><p><br>Our results show that induction heating may have been significant in the past, leading to local temperature increases of several hundreds of Kelvin (see Fig. 1). This early heating leads to an earlier depletion of the interior and volatile outgassing compared to if the planet would not have been subject to induction heating. We show that induction heating has an impact comparable to tidal heating when assuming latest estimates on its eccentricity. We furthermore find that the planet mass (linked to the planetary orbital inclination) has a first-order influence on the efficiency of outgassing from the interior.</p><p> </p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.53bcd48f2cff56572630161/sdaolpUECMynit/12UGE&app=m&a=0&c=314fe555893c77417d52bf9a6bd3825f&ct=x&pn=gnp.elif&d=1" alt="" width="307" height="339"> </p><p>Fig 1: Local induction heating and resulting temperature variations compared to a simulation without induction heating after 1 Gyr of thermal evolution for an example rocky planet of 1.8 Earth masses with an iron content of 20 wt-%.</p>

Thermal Physics of Cometary Nuclei

2020 ◽  
Author(s):  
Dina Prialnik
Keyword(s):  
Solar Energy ◽  
Thermal Emission ◽  
Thermal Evolution ◽  
Internal Heat ◽  
Thermal Inertia ◽  
Skin Depth ◽  
Physical Models ◽  
The Sun ◽  
Cometary Nuclei ◽  
Water Ice

Cometary nuclei, as small, spinning, ice-rich objects revolving around the sun in eccentric orbits, are powered and activated by solar radiation. Far from the sun, most of the solar energy is reradiated as thermal emission, whereas close to the sun, it is absorbed by sublimation of ice. Only a small fraction of the solar energy is conducted into the nucleus interior. The rate of heat conduction determines how deep and how fast this energy is dissipated. The conductivity of cometary nuclei, which depends on their composition and porosity, is estimated based on vastly different models ranging from very simple to extremely complex. The characteristic response to heating is determined by the skin depth, the thermal inertia, and the thermal diffusion timescale, which depend on the comet’s structure and dynamics. Internal heat sources include the temperature-dependent crystallization of amorphous water ice, which becomes important at temperatures above about 130 K; occurs in spurts; and releases volatiles trapped in the ice. These, in turn, contribute to heat transfer by advection and by phase transitions. Radiogenic heating resulting from the decay of short-lived unstable nuclei such as 26Al heats the nucleus shortly after formation and may lead to compositional alterations. The thermal evolution of the nucleus is described by thermo-physical models that solve mass and energy conservation equations in various geometries, sometimes very complicated, taking into account self-heating. Solutions are compared with actual measurements from spacecraft, mainly during the Rosetta mission, to deduce the thermal properties of the nucleus and decipher its activity pattern.

Effects of Cyclodextrin Solutions on Methane Hydrate Formation

2007 ◽  
Author(s):  
Ryo Nozawa ◽  
Mohammad Ferdows ◽  
Kazuhiko Murakami ◽  
Masahiro Ota
Keyword(s):  
Raman Spectroscopy ◽  
Induction Time ◽  
Methane Hydrate ◽  
Methane Concentration ◽  
Formation Rate ◽  
Hydrate Formation ◽  
Formation Water ◽  
Advanced Method

In this paper, we suggest the advanced method of methane hydrate formation by cyclodextrin solutions. The structures of the methane hydrate were experimentally investigated by Raman spectroscopy. The induction time of the methane hydrate formation becomes by shorter 10–30 times and formation rate become by faster 2–4 times originated in the increased methane concentration of hydrate formation water by adding cyclodextrins. The results by the Raman spectroscopy indicate that the structure I methane hydrate is produced and methane molecules exist in both Large and Small cages.

Methane Hydrate Nucleation Rates from Molecular Dynamics Simulations: Effects of Aqueous Methane Concentration, Interfacial Curvature, and System Size

2011 ◽  
Vol 115 (43) ◽  
pp. 21241-21248 ◽  
Author(s):  
Matthew R. Walsh ◽  
Gregg T. Beckham ◽  
Carolyn A. Koh ◽  
E. Dendy Sloan ◽  
David T. Wu ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Methane Hydrate ◽  
Methane Concentration ◽  
System Size ◽  
Dynamics Simulations

604 Dissociation of Methane Hydrate in Okhotsk Sea : Survey of Methane Concentration in Sea Water and Sea Ice

2001 ◽  
Vol 2001.41 (0) ◽  
pp. 198-199
Author(s):  
Naoyuki OHASHI ◽  
Eiji TSUKAHARA ◽  
Masafumi SASAKI ◽  
Noboru ENDOH
Keyword(s):  
Sea Ice ◽  
Methane Hydrate ◽  
Methane Concentration ◽  
Sea Water ◽  
Okhotsk Sea

Intracerebroventricular physostigmine facilitates heat loss mechanisms in running rats

2004 ◽  
Vol 97 (1) ◽  
pp. 333-338 ◽  
Author(s):  
Alex G. Rodrigues ◽  
Nilo R. V. Lima ◽  
Cândido C. Coimbra ◽  
Umeko Marubayashi
Keyword(s):  
Metabolic Rate ◽  
Heating Rate ◽  
Core Temperature ◽  
Heat Dissipation ◽  
Heat Storage ◽  
Treated Group ◽  
Lower Heat ◽  
Exercise Induced ◽  
Colonic Temperature ◽  
Lateral Cerebral Ventricle

The aim of this study was to evaluate the participation of central cholinergic transmission in the regulation of metabolic rate, core temperature, and heat storage in untrained rats submitted to exercise on a treadmill (20 m/min, 5% inclination) until fatigue. The animals were separated into eight experimental groups, and core temperature or metabolic rate was measured in the rats while they were exercising or while they were at rest after injection of 2 μl of 5 × 10−3 M physostigmine (Phy) or 0.15 M NaCl solution (Sal) into the lateral cerebral ventricle. Metabolic rate was determined by the indirect calorimetry system, and colonic temperature was recorded as an index of core temperature. In resting animals, Phy induced only a small increase in metabolic rate compared with Sal injection, without having any effect on core temperature. During exercise, the Phy-treated animals showed a lower core heating rate (0.022 ± 0.003°C/min Phy vs. 0.033 ± 0.003°C/min Sal; P < 0.02), lower heat storage (285 ± 37 cal Phy vs. 436 ± 34 cal Sal; P < 0.02) and lower core temperature at fatigue point than the Sal-treated group (38.5 ± 0.1°C Phy vs. 39.0 ± 0.1°C Sal; P < 0.05). However, despite the lower core heating rate, heat storage, and core temperature at fatigue, the Phy-treated rats showed a similar running time compared with the Sal-treated group. We conclude that the activation of the central cholinergic system during exercise increases heat dissipation and attenuates the exercise-induced increase in core temperature without affecting running performance.

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