Tidal Heating of Earth-like Exoplanets around M Stars: Thermal, Magnetic, and Orbital Evolutions

Driscoll, Peter; Barnes, Rory

doi:10.1089/ast.2015.1325

Cited by 118 publications

(109 citation statements)

References 75 publications

(153 reference statements)

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“…The denominator of (22) is the sum of core specific heat and heat released by inner core growth, where A ic is inner core surface area, ρ ic is inner core density, ϵ c is a constant that relates average core temperature to CMB temperature,

d R_{i c} / d T_{c m b}

is the rate of inner core growth as a function of CMB temperature, and L Fe and E G are the latent and gravitational energy released at the ICB per unit mass. Detailed expressions for heat flows and temperature profiles as functions of mantle and core properties are given in Driscoll and Bercovici [] and Driscoll and Barnes [].…”

Section: Generation Of the Magnetic Field And Its Role In Atmosphericmentioning

confidence: 99%

“…Thus, a better understanding of how and when volatiles are delivered during accretion, how much degassing occurs during accretion and solidification of a possible magma ocean, and how much atmospheric loss occurs during this early phase of planetary history are all necessary for constraining planetary evolution. Can strong gravitational tides render a planet uninhabitable? Planets experiencing strong gravitational tides (caused by nearby stars, planets, or satellites) can generate significant internal heating via tidal dissipation, which can cause extreme surface volcanism and hinder dynamo action [ Driscoll and Barnes , ]. Efficient cooling of the interior could allow the orbits of such planets to circularize faster, minimizing the length of time spent in a tidally heated regime, and could move the planet in (or out) of the habitable zone.…”

Section: Future Directionsmentioning

confidence: 99%

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Whole planet coupling between climate, mantle, and core: Implications for rocky planet evolution

Foley

Driscoll

2016

Geochem Geophys Geosyst

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Earth's climate, mantle, and core interact over geologic timescales. Climate influences whether plate tectonics can take place on a planet, with cool climates being favorable for plate tectonics because they enhance stresses in the lithosphere, suppress plate boundary annealing, and promote hydration and weakening of the lithosphere. Plate tectonics plays a vital role in the long-term carbon cycle, which helps to maintain a temperate climate. Plate tectonics provides long-term cooling of the core, which is vital for generating a magnetic field, and the magnetic field is capable of shielding atmospheric volatiles from the solar wind. Coupling between climate, mantle, and core can potentially explain the divergent evolution of Earth and Venus. As Venus lies too close to the sun for liquid water to exist, there is no long-term carbon cycle and thus an extremely hot climate. Therefore plate tectonics cannot operate and a long-lived core dynamo cannot be sustained due to insufficient core cooling. On planets within the habitable zone where liquid water is possible, a wide range of evolutionary scenarios can take place depending on initial atmospheric composition, bulk volatile content, or the timing of when plate tectonics initiates, among other factors. Many of these evolutionary trajectories would render the planet uninhabitable. However, there is still significant uncertainty over the nature of the coupling between climate, mantle, and core. Future work is needed to constrain potential evolutionary scenarios and the likelihood of an Earth-like evolution.

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d R_{i c} / d T_{c m b}

Section: Generation Of the Magnetic Field And Its Role In Atmosphericmentioning

confidence: 99%

Section: Future Directionsmentioning

confidence: 99%

Whole planet coupling between climate, mantle, and core: Implications for rocky planet evolution

Foley

Driscoll

2016

Geochem Geophys Geosyst

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“…Tidal heating may at some given time maintain a liquid ocean, but if that heat disappears the moon is frozen solid. Driscoll & Barnes (2015) studied the tidal evolution of planetary orbits in M dwarf systems (similar in scale to the Jovian system) and find that the closer in a planet orbits, independent of initial eccentricity, the sooner their orbits circularize. For a planet with a 0.01 AU semi-major axis (approximately the semi-major axis of Titan around Saturn), an orbit with an initial eccentricity of 0.5 circularizes entirely within 1 million years after intense tidal heat dissipation.…”

Section: Timescales and Implications For Fiducial Moonsmentioning

confidence: 99%

The subsurface habitability of small, icy exomoons

Tjoa

Mueller

Tak

2020

A&A

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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 & 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.

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“…Taking the upper limit of the expected radius of Proxima Cen b, 1.4 R ⊕ , this gives a magnetic moment of ∼0.8M ⊕ , which agrees with the upper limit of Zuluaga & Bustamante (2016). However, Driscoll & Barnes (2015) showed that for an Earth-like terrestrial planet orbiting a star of 0.1 M with high initial eccentricity (e ≥0.1) within 0.07 AU, the planet will circularize before 10 Gyr. On this timescale, the orbital energy dissipated as tidal heating is sufficient to drive a strong convective flow in the planetary interior that could generate a magnetic moment in the range of ∼0.8 − 2.0M ⊕ during the process of circularization.…”

Section: Magnetic Dipole Moment Of Proxima Cen Bmentioning

confidence: 99%

The Pale Green Dot: A Method to Characterize Proxima Centauri b Using Exo-Aurorae

Luger

Lustig‐Yaeger

Fleming

et al. 2017

ApJ

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We examine the feasibility of detecting auroral emission from the potentially habitable exoplanet Proxima Centauri b. Detection of aurorae would yield an independent confirmation of the planet's existence, constrain the presence and composition of its atmosphere, and determine the planet's eccentricity and inclination, thereby breaking the mass-inclination degeneracy. If Proxima Centauri b is a terrestrial world with an Earth-like atmosphere and magnetic field, we estimate the power at the 5577Å OI auroral line is on the order of 0.1 TW under steady-state stellar wind, or ∼100× stronger than that on Earth. This corresponds to a planet-star contrast ratio of 10 −6 − 10 −7 in a narrow band about the 5577Å line, although higher contrast (10 −4 − 10 −5 ) may be possible during periods of strong magnetospheric disturbance (auroral power 1 − 10 TW). We searched the Proxima Centauri b HARPS data for the 5577Å line and for other prominent oxygen and nitrogen lines, but find no signal, indicating that the OI auroral line contrast must be lower than 2 × 10 −2 (with power 3,000 TW), consistent with our predictions. We find that observations of 0.1 TW auroral emission lines are likely infeasible with current and planned telescopes. However, future observations with a space-based coronagraphic telescope or a ground-based extremely large telescope (ELT) with a coronagraph could push sensitivity down to terawatt oxygen aurorae (contrast 7 × 10 −6 ) with exposure times of ∼1 day. If a coronagraph design contrast of 10 −7 can be achieved with negligible instrumental noise, a future concept ELT could observe steady-state auroral emission in a few nights.

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Tidal Heating of Earth-like Exoplanets around M Stars: Thermal, Magnetic, and Orbital Evolutions

Cited by 118 publications

References 75 publications

Whole planet coupling between climate, mantle, and core: Implications for rocky planet evolution

Whole planet coupling between climate, mantle, and core: Implications for rocky planet evolution

The subsurface habitability of small, icy exomoons

The Pale Green Dot: A Method to Characterize Proxima Centauri b Using Exo-Aurorae

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