ATMOSPHERIC ESCAPE FROM HOT JUPITERS

By R. Murray-Clay, E. Chiang, N. Murray. 2008

387 citations recorded by the source corpus.

Photoionization heating from ultraviolet (UV) radiation incidents on the atmospheres of hot Jupiters may drive planetary mass loss. Observations of stellar Lyman-α (Lyα) absorption have suggested that the hot Jupiter HD 209458b is losing atomic hydrogen. We construct a model of escape that includes realistic heating and cooling, ionization balance, tidal gravity, and pressure confinement by the host star wind. We show that mass loss takes the form of a hydrodynamic (Parker) wind, emitted from the planet's dayside during lulls in the stellar wind. When dayside winds are suppressed by the confining action of the stellar wind, nightside winds might pick up if there is sufficient horizontal transport of heat. A hot Jupiter loses mass at maximum rates of ∼2 × 1012 g s−1 during its host star's pre-main-sequence phase and ∼2 × 1010 g s−1 during the star's main-sequence lifetime, for total maximum losses of ∼0.06% and ∼0.6% of the planet's mass, respectively. For UV fluxes FUV ≲ 104 erg cm−2 s−1, the mass-loss rate is approximately energy limited and scales as . For larger UV fluxes, such as those typical of T Tauri stars, radiative losses and plasma recombination force to increase more slowly as F0.6UV. Dayside winds are quenched during the T Tauri phase because of confinement by overwhelming stellar wind pressure. During this early stage, nightside winds can still blow if the planet resides outside the stellar Alfvén radius; otherwise, even nightside winds are stifled by stellar magnetic pressure, and mass loss is restricted to polar regions. We conclude that while UV radiation can indeed drive winds from hot Jupiters, such winds cannot significantly alter planetary masses during any evolutionary stage. They can, however, produce observable signatures. Candidates for explaining why the Lyman-α photons of HD 209458 are absorbed at Doppler-shifted velocities of ±100 km s−1 include charge-exchange in the shock between the planetary and stellar winds.

Subfields: Astronomy and Astrophysics, Statistical and Nonlinear Physics

View Paper: https://www.semanticscholar.org/paper/8cf1b7597ed965cfe77dcccd6c89d14cfd9b1227

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In Astronomy and Astrophysics

1. Jon Fortney
2. J. Owen
3. C. Mordasini
4. N. Madhusudhan
5. Sara Seager
6. Yanqin Wu
7. D. Charbonneau
8. A. Showman

In Statistical and Nonlinear Physics

1. Jon Fortney
2. Y. Lithwick
3. C. Mordasini
4. J. Owen
5. Yanqin Wu
6. Leslie A. Rogers
7. Sara Seager
8. V. Parmentier

Citations in the corpus

• HYDROGEN GREENHOUSE PLANETS BEYOND THE HABITABLE ZONE (2011, background): “Lyman-α radiation resonantly scatters at higher altitudes (N ∼ 1× 1017 m−2) but, in the absence of an absorber such as atomic oxygen, will escape before being thermalized (Murray-Clay et al. 2009).”
• Evaporation of the planet HD 189733b observed in H I Lyman-α (2010, neutral): “…explain and characterize the evaporation processes (Lammer et al. 2003; Lecavelier des Etangs et al. 2004, 2007, 2008a; Baraffe et al. 2004, 2005, 2006; Yelle 2004, 2006; Jaritz et al. 2005; Tian et al. 2005; Garćıa-Muñoz 2007; Holmström et al. 2008; Stone & Proga 2009; Murray-Clay et al. 2009).”
• POSSIBLE DISINTEGRATING SHORT-PERIOD SUPER-MERCURY ORBITING KIC 12557548 (2012, background): “As noted above, a first-principles calculation of Ṁd along the lines of the externally irradiated solution for hot Jupiter winds (e.g., Murray-Clay et al. 2009) would be welcome.”
• Temporal variations in the evaporating atmosphere of the exoplanet HD 189733b (2012, background): “…at short orbital distances, the physics of the exospheric gas and role of the star-planet system properties remain debated (Garcı́a Munõz 2007; Schneiter et al. 2007; Holmström et al. 2008; Lecavelier des Etangs et al. 2008; Murray-Clay et al. 2009; Ben-Jaffel & Sona Hosseini 2010; Guo 2011).”
• WATER LOSS FROM TERRESTRIAL PLANETS WITH CO2-RICH ATMOSPHERES (2013, neutral): “dergoing water loss should be atomic H, not H 2. Atomic hydrogen absorbs hard XUV radiation by ionization at wavelengths below 91 nm with an ionization heating eciency of 0.15-0.3 (Chasseere 1996; Murray-Clay et al. 2009), and has a low collision cross-section, leading to high thermal conductivity (”
• Characterization of exoplanets from their formation - II. The planetary mass-radius relationship (2012, background): “Second, we do not take into account that planets close to the star can loose parts of their gaseous envelope due to evaporation (e.g. Lammer et al. 2009; Murray-Clay et al. 2009).”
• The Evaporation Valley in the Kepler Planets (2017, background): “…than X1/3; photon-limited evaporation (Owen & Alvarez 2016), where the radius increases faster than X1/2; and recombination limited evaporation (Murray-Clay et al. 2009), where the mass-loss rate is exponentially sensitive to radius (Owen & Alvarez 2016) such that the erosion time-scale…”
• THE IMPRINT OF EXOPLANET FORMATION HISTORY ON OBSERVABLE PRESENT-DAY SPECTRA OF HOT JUPITERS (2016, background): “…Jin et al. 2014), the envelope evaporation rate due to EUV irradiation is modeled at high EUV fluxes with a radiation-recombination limited rate (Murray-Clay et al. 2009) as dMrr−lim dt = 4πρscsr2s (A12) where ρs and cs are the density and sound speed at the sonic point which is located at a…”
• The Cosmic Shoreline: The Evidence that Escape Determines which Planets Have Atmospheres, and what this May Mean for Proxima Centauri B (2017, methodology): “In a hydrocode simulation of an XUV-heated wind, the lower boundary condition can be justified a postiori as self-consistent for a particular model by showing the model to be insensitive to changing it (e.g., Watson et al. 1981; Murray-Clay et al. 2009; Owen and Alvarez 2016).”
• MIGRATION THEN ASSEMBLY: FORMATION OF NEPTUNE-MASS PLANETS INSIDE 1 AU (2011, background): “It has been suggested by numerous authors that short-period planets may experience significant atmospheric mass loss driven by irradiation from the central star (e.g., Lammer et al. 2003; Yelle 2004; Lecavelier des Etangs et al. 2004; Tian et al. 2005; Murray-Clay et al. 2009).”
• ALL SIX PLANETS KNOWN TO ORBIT KEPLER-11 HAVE LOW DENSITIES (2013, background): “In particular, more irradiated planets like Kepler-11 b and c lose more energy to radiation and recombination-driven cooling, resulting in lower mass-loss efficiencies and thus a higher threshold in Figure 10 (Murray-Clay et al. 2009).”
• Photoevaporation and high-eccentricity migration created the sub-Jovian desert (2018, background): “However, detailed radiationhydrodynamic photoevaporation models (e.g. Murray-Clay et al. 2009; Owen & Jackson 2012; Tripathi et al. 2015; Owen & Alvarez 2016) indicate that strong photoevporation of giant planets is difficult, and removing a giant planet’s entire H/He atmosphere is impossible, even…”
• HOW THERMAL EVOLUTION AND MASS-LOSS SCULPT POPULATIONS OF SUPER-EARTHS AND SUB-NEPTUNES: APPLICATION TO THE KEPLER-11 SYSTEM AND BEYOND (2012, background): “Murray-Clay et al. (2009) found that at XUV fluxes over 105 erg s−1 cm−2, relevant for many hot Jupiters, mass loss becomes radiation/recombination-limited and highly inefficient.”
• PLANETARY POPULATION SYNTHESIS COUPLED WITH ATMOSPHERIC ESCAPE: A STATISTICAL VIEW OF EVAPORATION (2014, methodology): “The mass-loss rate increases slowly with the incoming flux as Ṁ ∝ F 0.6EUV (Murray-Clay et al. 2009).”
• LYα TRANSIT SPECTROSCOPY AND THE NEUTRAL HYDROGEN TAIL OF THE HOT NEPTUNE GJ 436b (2014, methodology): “(10) While Murray-Clay et al. (2009) predict v to vary by a factor of a few over the range of p considered here, we have approximated v to be constant with p.”
• The Interior Structure, Composition, and Evolution of Giant Planets (2009, result): “Current models of atmospheric escape from hot Jupiters (e.g. Murray-Clay et al. 2009) find evaporation rates much lower than those previously assumed by Baraffe and collaborators, which were based on earlier work.”
• FORMATION AND STRUCTURE OF LOW-DENSITY EXO-NEPTUNES (2011, methodology): “We estimate RXUV following order-of-magnitude arguments gleaned from Section 2 of Murray-Clay et al. (2009), RXUV ≈ Rp +HR ln ( PRR 2 XUV NHmHGMp ) , (14) where NH ∼ 5 × 1021 m−2 is roughly the column of neutral hydrogen needed to reach τXUV ∼ 1, PR is the pressure at Rp, and HR is the pressure…”
• MASS TRANSFER, TRANSITING STREAM, AND MAGNETOPAUSE IN CLOSE-IN EXOPLANETARY SYSTEMS WITH APPLICATIONS TO WASP-12 (2010, background): “…wind – such a wind has been studied extensively in the context of hot Jupiter HD 209458b (e.g., Yelle 2004; Tian et al. 2005; Garcia Munoz 2007; Murray-Clay et al. 2009): The wind is most strongly generated at the planet’s dayside, and would be distributed on both sides (terminations) of the…”
• Core-powered mass-loss and the radius distribution of small exoplanets (2017, background): “…(see also Ikoma & Hori 2012; Owen & Wu 2016) a process of spontaneous mass loss that is essentially different from (and complementary to) the high-energy photoevaporation that is usually discussed in the literature (Murray-Clay et al. 2009; Lopez et al. 2012; Owen & Jackson 2012; Owen & Wu 2013).”