Limits on the orbits and masses of moons around currently-known transiting exoplanets

Weidner, C.; Horne, K.

doi:10.1051/0004-6361/201014955

Cited by 36 publications

(44 citation statements)

References 57 publications

(72 reference statements)

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“…In the present investigation the effects of the binary eccentricity and inclination on the Hill stability will also be determined for all the currently known transiting extrasolar planet systems where the mass is known. It should be noted that Weidner and Horne (2010) found that the majority of Hill radii derived from Domingos et al (2006) agreed within better than 10 % with those derived by Donnison (2010a) for the 43 extrasolar planets common to both samples. To proceed further we now consider Hill stability in some detail.…”

Section: Stability Limitsmentioning

confidence: 61%

Limits on the Orbits of Possible Eccentric and Inclined Moons of Extrasolar Planets Orbiting Single Stars

Donnison

2014

Earth Moon Planets

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Limits are placed on the range of orbits and masses of possible moons orbiting extrasolar planets which orbit single central stars. The Roche limiting radius determines how close the moon can approach the planet before tidal disruption occurs; while the Hill stability of the star-planet-moon system determines stable orbits of the moon around the planet. Here the full three-body Hill stability is derived for a system with the binary composed of the planet and moon moving on an inclined, elliptical orbit relative the central star. The approximation derived here in Eq. (17) assumes the binary mass is very small compared with the mass of the star and has not previously been applied to this problem and gives the criterion against disruption and component exchange in a closed form. This criterion was applied to transiting extrasolar planetary systems discovered since the last estimation of the critical separations (Donnison in Mon Not R Astron Soc 406:1918, 2010a) for a variety of planet/ moon ratios including binary planets, with the moon moving on a circular orbit. The effects of eccentricity and inclination of the binary on the stability of the orbit of a moon is discussed and applied to the transiting extrasolar planets, assuming the same planet/moon ratios but with the moon moving with a variety of eccentricities and inclinations. For the non-zero values of the eccentricity of the moon, the critical separation distance decreased as the eccentricity increased in value. Similarly the critical separation decreased as the inclination increased. In both cases the changes though very small were significant.

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Section: Stability Limitsmentioning

confidence: 61%

Limits on the Orbits of Possible Eccentric and Inclined Moons of Extrasolar Planets Orbiting Single Stars

Donnison

2014

Earth Moon Planets

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“…Only the position of Earth's moon, which receives a maximum of 0.35 W/m 2 reflected light from Earth, reproduces the true Solar System values. The Roche radius for a fluid-like body (Weidner and Horne, 2010, and references therein) is indicated with a gray line at 2.07R p .…”

Section: Heller and Barnesmentioning

confidence: 99%

Exomoon Habitability Constrained by Illumination and Tidal Heating

2013

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The detection of moons orbiting extrasolar planets (''exomoons'') has now become feasible. Once they are discovered in the circumstellar habitable zone, questions about their habitability will emerge. Exomoons are likely to be tidally locked to their planet and hence experience days much shorter than their orbital period around the star and have seasons, all of which works in favor of habitability. These satellites can receive more illumination per area than their host planets, as the planet reflects stellar light and emits thermal photons. On the contrary, eclipses can significantly alter local climates on exomoons by reducing stellar illumination. In addition to radiative heating, tidal heating can be very large on exomoons, possibly even large enough for sterilization. We identify combinations of physical and orbital parameters for which radiative and tidal heating are strong enough to trigger a runaway greenhouse. By analogy with the circumstellar habitable zone, these constraints define a circumplanetary ''habitable edge.'' We apply our model to hypothetical moons around the recently discovered exoplanet Kepler-22b and the giant planet candidate KOI211.01 and describe, for the first time, the orbits of habitable exomoons. If either planet hosted a satellite at a distance greater than 10 planetary radii, then this could indicate the presence of a habitable moon.

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“…So far, no extrasolar moon has been confirmed, but dedicated surveys are underway (Kipping et al 2012). Several studies have addressed orbital stability of extrasolar satellite systems (Donnison 2010;Weidner & Horne 2010) and tidal heating has been shown to be an important energy source in satellites (Reynolds et al 1987;Scharf 2006;Cassidy et al 2009). In a recent study (Heller & Barnes 2012, HB12 in the following), we have extended these concepts to the illumination from the planet, i.e.…”

Section: Introductionmentioning

confidence: 99%

Exomoon habitability constrained by energy flux and orbital stability

Heller

2012

A&A

106

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Context. Detecting massive satellites that orbit extrasolar planets has now become feasible, which led naturally to questions about the habitability of exomoons. In a previous study we presented constraints on the habitability of moons from stellar and planetary illumination as well as from tidal heating. Aims. Here I refine our model by including the effect of eclipses on the orbit-averaged illumination. I then apply an analytic approximation for the Hill stability of a satellite to identify the range of stellar and planetary masses in which moons can be habitable. Moons in low-mass stellar systems must orbit their planet very closely to remain bounded, which puts them at risk of strong tidal heating. Methods. I first describe the effect of eclipses on the stellar illumination of satellites. Then I calculate the orbit-averaged energy flux, which includes illumination from the planet and tidal heating to parametrize exomoon habitability as a function of stellar mass, planetary mass, and planet-moon orbital eccentricity. The habitability limit is defined by a scaling relation at which a moon loses its water by the runaway greenhouse process. As a working hypothesis, orbital stability is assumed if the moon's orbital period is less than 1/9 of the planet's orbital period. Results. Due to eclipses, a satellite in a close orbit can experience a reduction in orbit-averaged stellar flux by up to about 6%. The smaller the semi-major axis and the lower the inclination of the moon's orbit, the stronger the reduction. I find a lower mass limit of ≈0.2 M for exomoon host stars that allows a moon to receive an orbit-averaged stellar flux comparable to the Earth's, with which it can also avoid the runaway greenhouse effect. Precise estimates depend on the satellite's orbital eccentricity. Deleterious effects on exomoon habitability may occur up to ≈0.5 M if the satellite's eccentricity is 0.05. Conclusions. Although the traditional habitable zone lies close to low-mass stars, which allows for many transits of planet-moon binaries within a given observation cycle, resources should not be spent to trace habitable satellites around them. Gravitational perturbations by the close star, another planet, or another satellite induce eccentricities that likely make any moon uninhabitable. Estimates for individual systems require dynamical simulations that include perturbations among all bodies and tidal heating in the satellite.

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Limits on the orbits and masses of moons around currently-known transiting exoplanets

Cited by 36 publications

References 57 publications

Limits on the Orbits of Possible Eccentric and Inclined Moons of Extrasolar Planets Orbiting Single Stars

Limits on the Orbits of Possible Eccentric and Inclined Moons of Extrasolar Planets Orbiting Single Stars

Exomoon Habitability Constrained by Illumination and Tidal Heating

Exomoon habitability constrained by energy flux and orbital stability

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