A diagram to determine the evaporation status of extrasolar planets

By A. Lecavelier, Des Etangs. 2006

219 citations recorded by the source corpus.

Aims. To describe the evaporation status of extrasolar planets, we consider an energy diagram in which the potential energy of the planets is plotted versus the energy received by the upper atmosphere. Methods. Here we present a basic method to estimate these quantities. For the potential energy, we include the modification of the gravity field by the tidal forces from the parent stars. Results. This description allows a rapid estimate of both the escape rate of the atmospheric gas and the lifetime of a planet against the evaporation process. In the energy diagram, we find an evaporation-forbidden region in which a gaseous planet would evaporate in less than 5 billion years. With their observed characteristics, all extrasolar planets are found outside this evaporation-forbidden region. The escape rates are estimated to be in the range 10 5 g s -1 to 10 12 g s -1 with a few cases above 10 11 g s -1 . The estimated escape rate for HD 209458 b is consistent with the lower limit of 10 10 g s -1 obtained from interpretation of the H I Lyman-α observations. This diagram suggests possibilities for the nature of the recently discovered Neptune-mass planets. We find that GJ 436 b, 55 Cnc e and HD 69830 b cannot be low mass gaseous planets. With a density that must be above 0.5 g cm -3 to survive evaporation, these planets must contain a large fraction of solid/liquid material. We find that GJ 876 d must have a density greater than ∼3 g cm -3 to survive the strong EUV energy flux from its nearby parent star. GJ 876 d must contain a large fraction of massive elements.

Subfields: Astronomy and Astrophysics, Instrumentation, Statistical and Nonlinear Physics

View Paper: https://www.semanticscholar.org/paper/024cc0e4a99f61397a86e15dd0ed466614e3f887

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In Astronomy and Astrophysics

1. Jon Fortney
2. J. Owen
3. D. Charbonneau
4. Timothy Morton
5. J. Winn
6. J. Johnson
7. Sara Seager
8. Yanqin Wu

In Instrumentation

1. D. Charbonneau
2. Jon Fortney
3. Timothy Morton
4. J. Owen
5. J. Winn
6. J. Johnson
7. G. Marcy
8. Yanqin Wu

In Statistical and Nonlinear Physics

1. J. Owen
2. Timothy Morton
3. Yanqin Wu
4. Jon Fortney
5. Leslie A. Rogers
6. D. Charbonneau
7. J. Johnson
8. Sara Seager

Citations in the corpus

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• ALL SIX PLANETS KNOWN TO ORBIT KEPLER-11 HAVE LOW DENSITIES (2013, background): “…lines with slope = 1) in this space correspond to constant mass-loss timescales for a specified mean molecular weight of escaping gas, making this diagram useful for understanding how the population of highly irradiated planets has been sculpted by photoevaporation (Lecavelier des Etangs 2007).”
• Evaporation of the planet HD 189733b observed in H I Lyman-α (2010, background): “In effect, theoretical models of the evaporation of hot Jupiters agree to conclude that the escape rate can be estimated by assuming that the EUV and X-ray energy input from the star is used by the gas to escape the gravitation of the planet (Lecavelier des Etangs 2007).”
• The escape of heavy atoms from the ionosphere of HD209458b. I. A photochemical–dynamical model of the thermosphere (2012, background): “These types of results have implications on statis-87 tical studies that characterize the escape of planetary atmospheres by relying88 on the so-called energy-limited escape (e.g., Watson et al., 1981; Lecavelier89 des Etangs, 2007; Sanz-Forcada et al., 2010).”
• TIDAL EVOLUTION OF CLOSE-IN PLANETS (2010, background): “The orbits of these planets might have been circularized as the planet lost mass (e.g. Lammer et al. 2003; Lecavelier Des Etangs 2007), or the planetary radius expanded due to tidal heating (e.g. Bodenheimer et al. 2001; Gu et al. 2003).”
• HAZMAT. I. THE EVOLUTION OF FAR-UV AND NEAR-UV EMISSION FROM EARLY M STARS (2014, methodology): “Lecavelier Des Etangs (2007) and Sanz-Forcada et al. (2011) estimate EUV fluxes in known, old, solar-type planet hosts using coronal models fits to X-ray spectra.”
• Estimation of the XUV radiation onto close planets and their evaporation (2011, background): “Lecavelier Des Etangs (2007) extrapolated the EUV flux from the X-ray-to-EUV ratio observed in the Sun, assuming the same ratio for all spectral types and activity levels (thus age).”
• Planetary evaporation by UV and X‐ray radiation: basic hydrodynamics (2012, background): “Perhaps the simplest approach is to assume that every photon received at the planet’s surface is turned into mass-loss at some efficiency (Watson et al. 1981; Lecavelier des Etangs 2007).”
• OBSERVATIONS OF MASS LOSS FROM THE TRANSITING EXOPLANET HD 209458b (2010, methodology): “By equating the energy input of both Lyman continuum and Lyman-α with stellar fluxes estimated from the rotation rate of HD 209458, Lecavelier des Etangs (2007) found Ṁ ∼ 3×1011 g s−1.”
• CHARACTERIZING THE COOL KOIs. IV. KEPLER-32 AS A PROTOTYPE FOR THE FORMATION OF COMPACT PLANETARY SYSTEMS THROUGHOUT THE GALAXY (2012, methodology): “Using an extreme ultraviolet luminosity of Kepler-32, LEUV ≈ 1026.6 (Hodgkin & Pye 1994) and following Lecavelier Des Etangs (2007) using a conservative mass loss efficiency of ǫUV = 0.1 we derive an atmospheric mass loss of ∼ 108 g s−1.”
• THREE POSSIBLE ORIGINS FOR THE GAS LAYER ON GJ 1214b (2009, methodology): “We calculate 2 × 106 kg s−1 for an energy-limited upper bound on the current mass-loss rate of GJ 1214b following the approximate approach of Lecavelier Des Etangs (2007).”
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• FORMATION AND STRUCTURE OF LOW-DENSITY EXO-NEPTUNES (2011, methodology): “We consider energy-limited mass loss, (e.g., Lammer et al. 2003; Lecavelier Des Etangs 2007; Valencia et al. 2010), Ṁ = − ǫπFXUV R 2 XUV Rp GMpKtide .”
• MIGRATION THEN ASSEMBLY: FORMATION OF NEPTUNE-MASS PLANETS INSIDE 1 AU (2011, methodology): “…exoplanets are based on the so-called energy diagram in which the gravitational binding energy of the planet (Ep) is compared to the energy input (Levap) from X-ray and EUV radiation (Lecavelier des Etangs 2007; Ehrenreich & Désert 2011), after accounting for various uncertain efficiency factors.”