Simulating the escaping atmospheres of hot gas planets in the solar neighborhood

Salz, M.; Czesla, S.; Schneider, P. C.; Schmitt, J. H. M. M.

doi:10.1051/0004-6361/201526109

Cited by 173 publications

(384 citation statements)

References 154 publications

(252 reference statements)

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“…Studies solving the kinetic Boltzmann equation applying a direct-simulation Monte Carlo model to calculate the heating efficiency indicate values between 10 and 20% (Shematovich et al 2014). We therefore adopt a heating efficiency of 15%, which is in good agreement with what obtained by Owen & Jackson (2012), Shematovich et al (2014), and Salz et al (2016).…”

Section: Hydrodynamic Upper Atmosphere Modelsupporting

confidence: 68%

Effect of stellar wind induced magnetic fields on planetary obstacles of non-magnetized hot Jupiters

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Lämmer

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We investigate the interaction between the magnetized stellar wind plasma and the partially ionized hydrodynamic hydrogen outflow from the escaping upper atmosphere of non-or weakly magnetized hot Jupiters. We use the well-studied hot Jupiter HD 209458b as an example for similar exoplanets, assuming a negligible intrinsic magnetic moment. For this planet, the stellar wind plasma interaction forms an obstacle in the planet's upper atmosphere, in which the position of the magnetopause is determined by the condition of pressure balance between the stellar wind and the expanded atmosphere, heated by the stellar extreme ultraviolet (EUV) radiation. We show that the neutral atmospheric atoms penetrate into the region dominated by the stellar wind, where they are ionized by photo-ionization and charge exchange, and then mixed with the stellar wind flow. Using a 3D magnetohydrodynamic (MHD) model, we show that an induced magnetic field forms in front of the planetary obstacle, which appears to be much stronger compared to those produced by the solar wind interaction with Venus and Mars. Depending on the stellar wind parameters, because of the induced magnetic field, the planetary obstacle can move up to ≈0.5-1 planetary radii closer to the planet. Finally, we discuss how estimations of the intrinsic magnetic moment of hot Jupiters can be inferred by coupling hydrodynamic upper planetary atmosphere and MHD stellar wind interaction models together with UV observations. In particular, we find that HD 209458b should likely have an intrinsic magnetic moment of 10-20% that of Jupiter.

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Section: Hydrodynamic Upper Atmosphere Modelsupporting

confidence: 68%

Effect of stellar wind induced magnetic fields on planetary obstacles of non-magnetized hot Jupiters

Еркаев

Odert

Lämmer

et al. 2017

Monthly Notices of the Royal Astronomical Society

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“…The third question is the general assumption of hydrodynamic escape, which is only valid if a planetary thermosphere is collisional up to the Roche-lobe height or the sonic point. Radiative heating cannot be converted into a bulk acceleration above the exobase, where the planetary atmosphere becomes collisionless; our definition of the exobase is given by Salz et al (2015b). In this case, a combined hydrodynamic and kinetic description has to be applied (e.g., Yelle 2004), which results in reduced mass-loss rates ranging between the Jeans escape rate and the hydrodynamic escape rate (cf.…”

Section: Energy-limited Escape Equationmentioning

confidence: 99%

“…Simulations: the transition from hydrodynamic winds to stable thermospheres Salz et al (2015b) presented simulations of the thermospheres of 18 hot gas planets in the solar neighborhood using 1D spherically symmetric simulations of the substellar point 1 Equation (1) is sometimes given with a factor of β 3 (e.g., Baraffe et al 2004;Sanz-Forcada et al 2010), but we favor β 2 (Watson et al 1981;Lammer et al 2003;Erkaev et al 2007). The equation contains R 3 pl in ρ pl , but one of the radii comes in via the gravitational potential.…”

Section: Energy-limited Escape Equationmentioning

confidence: 99%

“…We now compute the expansion radii and heating efficiencies for all simulations presented by Salz et al (2015b) plus our new simulations and derive scaling laws for the two factors. The resulting values are provided in Table A.1.…”

Section: Determining the Free Parameters In The Energy-limited Escapementioning

confidence: 99%

“…However, photoevaporative mass loss can play a more decisive role for the evolution of smaller gas or terrestrial planets. Salz et al (2015b) demonstrated that planets like 55 Cnc e may lose all volatiles over a planetary lifetime, eventually leaving a rocky super-Earth-type core behind. In fact, photoevaporative mass loss may be among the crucial factors determining the distribution of small close-in planets (Lecavelier des Etangs 2007;Carter et al 2012).…”

Section: Introductionmentioning

confidence: 99%

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Energy-limited escape revised

Salz

Schneider

Czesla

et al. 2015

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Gas planets in close proximity to their host stars experience photoevaporative mass loss. The energy-limited escape concept is generally used to derive estimates for the planetary mass-loss rates. Our photoionization hydrodynamics simulations of the thermospheres of hot gas planets show that the energy-limited escape concept is valid only for planets with a gravitational potential lower than log 10 (−Φ G ) < 13.11 erg g −1 because in these planets the radiative energy input is efficiently used to drive the planetary wind. Massive and compact planets with log 10 (−Φ G ) 13.6 erg g −1 exhibit more tightly bound atmospheres in which the complete radiative energy input is re-emitted through hydrogen Lyα and free-free emission. These planets therefore host hydrodynamically stable thermospheres. Between these two extremes the strength of the planetary winds rapidly declines as a result of a decreasing heating efficiency. Small planets undergo enhanced evaporation because they host expanded atmospheres that expose a larger surface to the stellar irradiation. We present scaling laws for the heating efficiency and the expansion radius that depend on the gravitational potential and irradiation level of the planet. The resulting revised energy-limited escape concept can be used to derive estimates for the mass-loss rates of super-Earth-sized planets as well as massive hot Jupiters with hydrogen-dominated atmospheres.

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Extrasolar planets and their hosts: A new X‐ray research area

Schmitt¹

2017

Astron Nachr

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The field of extrasolar planets has become one of the most lively and vibrant field of research in astrophysics. As is almost always the case in astrophysics, a multi-wavelength approach is required to fully explore and understand the properties of those planets. Also, X-ray astronomy plays an important role in this process. The host stars of essentially all extrasolar planets are (sometimes very vigorous) X-ray emitters, which can severely impact on the outer atmospheric layers of their planets. Furthermore, the close proximity between host stars and planets in the case of close-in "Hot Jupiters" may lead to magnetic or tidal interactions with observable consequences at X-ray wavelengths. I will address these issues and discuss how XMM-Newton can be used to advance the field. KEYWORDSExtrasolar planets, X-ray emission, stellar activity INTRODUCTIONWhen the science case for the X-ray observatory, which we now call XMM-Newton, was formulated in the early 1980s, extrasolar planets were nowhere on the agenda, and a proposal to study X-ray transits of extrasolar planets in front of their host stars would have likely met with a certain amount of skepticism. Today, we discuss issues like interactions between stars and extrasolar planets leading to observable effects at X-ray wavelengths subsumed under the name of star-planet interactions (SPIs) as well as X-ray transits. This clearly demonstrates that the newly emerged field of extrasolar planets has its ramifications in X-ray astronomy and especially in the field of stellar X-ray astronomy. Thus new research opportunities have opened up for XMM-Newton with its lifetime lasting (hopefully) until 2029, and I will attempt to illustrate some of the emerging research potential. EXTRASOLAR PLANETS AND THEIR HOSTSSince the discovery of the first extrasolar planet 51 Peg by Mayor & Queloz (1995), the research field "Extrasolar Planets" has virtually exploded over the last two decades. As of now, several thousand extrasolar planets are known with decent orbit determinations, and there are yet further thousands of planetary candidates, a large fraction of which is likely to be actual planets. It is interesting to consider the effective temperature distribution of the host stars with known planets, which is shown in Figure 1. As is clear from Figure 1, the observed distribution peaks at effective temperatures of ≈6000 K, that is, exactly in the range of solar-like stars. It is extremely likely that the observed effective temperature distribution is biased. Cooler stars are both intrinsically and apparently much fainter, yet it is believed that the frequency of planet occurrence around these stars does not differ from their warmer siblings. As far as the hotter stars are concerned, the higher radiation fields around these stars might prevent the formation of close-in planets; furthermore, any searches in radial velocity are hampered by the large rotation velocities of these stars, and potential transits are shallower for a given planet size, since these stars are so much brighter...

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Simulating the escaping atmospheres of hot gas planets in the solar neighborhood

Cited by 173 publications

References 154 publications

Effect of stellar wind induced magnetic fields on planetary obstacles of non-magnetized hot Jupiters

Effect of stellar wind induced magnetic fields on planetary obstacles of non-magnetized hot Jupiters

Energy-limited escape revised

Extrasolar planets and their hosts: A new X‐ray research area

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