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TOPIC: Super-Earths
Blobrana


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RE: Super-Earths
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Super-Earths 'in the billions'

There could be many billions of planets not much bigger than Earth circling faint stars in our galaxy, says an international team of astronomers.
The estimate for the number of "super-Earths" is based on detections already made and then extrapolated to include the Milky Way's population of so-called red dwarf stars.
The team works with the high-precision Harps instrument.
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Blobrana


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Super-Earth unlikely able to transfer life to other planets

While scientists believe conditions suitable for life might exist on the so-called "super-Earth" in the Gliese 581 system, it's unlikely to be transferred to other planets within that solar system.
Moon rocks and Mars meteorites have been found on Earth, which led Melosh to previously suggest living microbes could be exchanged among planets in a similar manner.
A Purdue research team has found that, in contrast to our own solar system, the exchange of living microbes between "super-Earth" and planets in that solar system is not likely to occur.
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Blobrana


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Super Earth Atmospheres
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Title: On the Stability of Super Earth Atmospheres
Authors: Kevin Heng, Pushkar Kopparla

We investigate the stability of super Earth atmospheres around M stars using a 7-parameter, analytical framework. We construct stability diagrams in the parameter space of exoplanetary radius versus semi-major axis and elucidate the regions in which stable atmospheres may exist. We find that super Earth atmospheres with higher mean molecular weights and enhanced metallicities occupy a smaller region of allowed parameter space, because of the dual effects of diminished advection and enhanced radiative cooling. Furthermore, many super Earths which reside within the habitable zones of M stars may not possess stable, Earth-like atmospheres. We apply our stability diagrams to GJ 436b and GJ 1214b, and demonstrate that Earth-like elemental compositions for their atmospheres are disfavoured if these exoplanets possess solid surfaces and shallow atmospheres. Finally, we construct stability diagrams tailored to the Kepler dataset, for G and K stars, and predict that about half of the exoplanetary candidates are expected to harbour stable atmospheres if Earth-like conditions are assumed. We include 55 Cancri e and CoRoT-7b in our stability diagram for G stars.

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Blobrana


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Title: Atmospheres of Hot Super-Earths
Authors: Thibaut Castan, Kristen Menou

Hot super-Earths likely possess minimal atmospheres established through vapour saturation equilibrium with the ground. We solve the hydrodynamics of these tenuous atmospheres at the surface of Corot-7b, Kepler 10b and 55 Cnc-e, including idealized treatments of magnetic drag and ohmic dissipation. We find that atmospheric pressures remain close to their local saturation values in all cases. Despite the emergence of strongly supersonic winds which carry sublimating mass away from the substellar point, the atmospheres do not extend much beyond the day-night terminators. Ground temperatures, which determine the planetary thermal (infrared) signature, are largely unaffected by exchanges with the atmosphere and thus follow the effective irradiation pattern. Atmospheric temperatures, however, which control cloud condensation and thus albedo properties, can deviate substantially from the irradiation pattern. Magnetic drag and ohmic dissipation can also strongly impact the atmospheric behaviour, depending on atmospheric composition and the planetary magnetic field strength. We conclude that hot super-Earths could exhibit interesting signatures in reflection (and possibly in emission) which would trace a combination of their ground, atmospheric and magnetic properties.

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Blobrana


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Title: Super-Earths: A New Class of Planetary Bodies
Authors: Nader Haghighipour

Super-Earths, a class of planetary bodies with masses ranging from a few Earth-masses to slightly smaller than Uranus, have recently found a special place in the exoplanetary science. Being slightly larger than a typical terrestrial planet, super-Earths may have physical and dynamical characteristics similar to those of Earth whereas unlike terrestrial planets, they are relatively easier to detect. Because of their sizes, super-Earths can maintain moderate atmospheres and possibly dynamic interiors with plate tectonics. They also seem to be more common around low-mass stars where the habitable zone is in closer distances. This article presents a review of the current state of research on super-Earths, and discusses the models of the formation, dynamical evolution, and possible habitability of these objects. Given the recent advances in detection techniques, the detectability of super-Earths is also discussed, and a review of the prospects of their detection in the habitable zones of low-mass stars is presented.

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Blobrana


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Habitable Super-Earths
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Title: On the Detection of (Habitable) Super-Earths Around Low-Mass Stars Using Kepler and Transit Timing Variation Method
Authors: Nader Haghighipour, Sabrina Kirste

We present the results of an extensive study of the detectability of Earth-sized planets and super-Earths in the habitable zones of cool and low-mass stars using transit timing variation method. We have considered a system consisting of a star, a transiting giant planet, and a terrestrial-class perturber, and calculated TTVs for different values of the parameters of the system. To identify ranges of the parameters for which these variations would be detectable by Kepler, we considered the analysis presented by Ford et al. (2011, ArXiv:1102.0544, PDF) and assumed that a peak-to-peak variation of 20 seconds would be within the range of the photometric sensitivity of this telescope. We carried out simulations for resonant and non-resonant orbits, and identified ranges of the semimajor axes and eccentricities of the transiting and perturbing bodies for which an Earth-sized planet or a super-Earth in the habitable zone of a low-mass star would produce such TTVs. Results of our simulations indicate that in general, outer perturbers near first- and second-order resonances show a higher prospect for detection. Inner perturbers are potentially detectable only when near 1:2 and 1:3 mean-motion resonances. For a typical M star with a Jupiter-mass transiting planet, for instance, an Earth-mass perturber in the habitable zone can produce detectable TTVs when the orbit of the transiting planet is between 15 and 80 days. We present the details of our simulations and discuss the implication of the results for the detection of terrestrial planets around different low-mass stars.

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Blobrana


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RE: Super-Earths
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Title: Hot Super Earths: disrupted young jupiters?
Authors: Sergei Nayakshin

Recent Kepler observations revealed an unexpected abundance of "hot" Earth-size to Neptune-size planets in the inner 0.02-0.2 AU from their parent stars. We propose that these smaller planets are the remnants of massive giant planets that migrated inward quicker than they could contract. We show that such disruptions naturally occur in the framework of the Tidal Downsizing hypothesis for planet formation. We find that the characteristic planet-star separation at which such "hot disruptions" occur is R \approx 0.03-0.2 AU. This result is independent of the planet's embryo mass but is dependent on the accretion rate in the disc. At high accretion rates, \dot M \simgt 10^{-6}\msun yr^{-1}, the embryo is unable to contract quickly enough and is disrupted. At late times, when the accretion rate drops to \dot M \simlt 10^{-8} \msun yr^{-1}, the embryos migrate sufficiently slow to not be disrupted. These "late arrivals" may explain the well known population of hot jupiters. If type I migration regime is inefficient, then our model predicts a pile-up of planets at R\sim 0.1 AU as the migration rate suddenly switches from the type II to type I in that region.

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Blobrana


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'Super-Earth' atmosphere measured

The atmosphere surrounding a "super-Earth" extrasolar planet has been measured for the first time.
The planet, GJ 1214b, is three times larger than Earth and about seven times heavier, and is the first planet of its kind known to have an atmosphere.
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Blobrana


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Earth-like planets 'may not be life-friendly'

A new study has revealed that planets like the Earth that we thought could support life, might not be life-friendly, and lack a protective magnetic field.
According to New Scientist, Super-Earths lack what makes life in Earth possible, a protective magnetic field.
Planets are thought to owe their magnetic fields to an iron core that is at least partly molten. But a simulation of super-Earths between a few times and 10 times Earth's mass suggests that high pressures will keep the core solid, according to Guillaume Morard of the Institute of Mineralogy and Physics of Condensed Matter in Paris, France, and his team.
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Blobrana


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Title: The melting curve of iron at extreme pressures: implications for planetary cores
Authors: G.Morard, J.Bouchet, D.Valencia, S.Mazevet, F.Guyot

Exoplanets with masses similar to that of Earth have recently been discovered in extrasolar systems. A first order question for understanding their dynamics is to know whether they possess Earth like liquid metallic cores. However, the iron melting curve is unknown at conditions corresponding to planets of several times the Earth's mass (over 1500 GPa for planets with 10 times the Earth's mass (ME)). In the density-temperature region of the cores of those super-Earths, we calculate the iron melting curve using first principle molecular dynamics simulations based on density functional theory. By comparing this melting curve with the calculated thermal structure of Super Earths, we show that planets heavier than 2ME, have solid cores, thus precluding the existence of an internal metallic-core driven magnetic field. The iron melting curve obtained in this study exhibits a steeper slope than any calculated planetary adiabatic temperature profile rendering the presence of molten metallic cores less likely as sizes of terrestrial planets increase.

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