On the Exospheric Temperature of Hydrogen-Dominated Planetary Atmospheres

Gross, S. H.

doi:10.1175/1520-0469(1972)029<0214:otetoh>2.0.co;2

Cited by 43 publications

(29 citation statements)

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“…The dynamics of the outflow of an expanding upper atmosphere against the pressure of the stellar wind may be considered to be similar to a comet's tail (Gross 1972;Schneider et al 1998;Moutou et al 2001). Because of the reduced magnetic moment resulting from tidal locking, our study indicates that the upper atmospheres of exoplanets orbiting at close distances around their host stars may be unprotected by their intrinsic magnetic fields over geological periods.…”

Section: Discussionmentioning

confidence: 63%

“…Lammer et al (2003a) found that if X reaches values <3 diffusive equilibrium no longer applies. For this case the thermal energy exceeds the gravitational potential energy (Öpik 1963;Bauer 1971;Gross 1972;Watson et al 1981)…”

Section: Atmosphere Protection and Erosionmentioning

confidence: 99%

“…In a recent study Lammer et al (2003a) estimated the exospheric temperature of "Hot Jupiters" by assuming that they have hydrogen rich upper atmospheres which are heated by the absorption of X-rays and extreme ultraviolet (XUV) radiation (Bauer 1971;Gross 1972;Watson et al 1981). Lammer et al (2003a) found that exospheric temperatures of the order of 10 4 K may develop at orbital distances <0.2 AU.…”

Section: Introductionmentioning

confidence: 99%

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The effect of tidal locking on the magnetospheric and atmospheric evolution of “Hot Jupiters”

Grießmeier

Stadelmann

Penz

et al. 2004

A&A

202

230

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Abstract. We study the interaction between the planetary magnetosphere and atmosphere of the close-in extrasolar planets HD 209458b and OGLE-TR-56b with the stellar wind during the evolution of their host stars. Recent astrophysical observations of solar-like stars indicate that the radiation and particle environments of young stars are orders of magnitudes larger than for stars with ages comparable to the sun (∼4.6 Gyr). We model the interaction for the present and for early evolutionary stages, showing that it is possible that "Hot Jupiters" have an ionosphere-stellar wind interaction like Venus. Our study suggests that the internal magnetic field of exoplanets orbiting close to their host stars may be very weak due to tidal locking. The magnetic moments can be less than one tenth of the value presently observed for the rapidly rotating planet Jupiter. We find that the stronger stellar wind of younger solar-type stars compresses the magnetosphere to a standoff distance at which the ionized part of the upper atmosphere, hydrodynamically expanded by the XUV-flux, builds an obstacle. Because of a much larger stellar wind particle flux during the first ∼0.5 Gyr after the host stars arrived on the Zero-Age-Main-Sequence, "Hot Jupiters" may have not been protected by their intrinsic magnetic fields, even if one neglects the effect of tidal locking. In such a case, the unshielded upper atmosphere will be affected by different ionization and non-thermal ion loss processes. This contributes to the estimated neutral hydrogen loss rates of about ≥10 10 g/s of the observed expanded exosphere of HD 209458b (Vidal-Madjar et al. 2003) and will be an ionized part of the estimated upper energy-limited neutral hydrogen loss rates of about 10 12 g/s (Lammer et al. 2003a).

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Section: Discussionmentioning

confidence: 63%

Section: Atmosphere Protection and Erosionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The effect of tidal locking on the magnetospheric and atmospheric evolution of “Hot Jupiters”

Grießmeier

Stadelmann

Penz

et al. 2004

A&A

202

230

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“…According to this theory, a gravitational potential energy well is formed around a planet at the exobase level which traps the planetary atmospheric constituents whenever the exobase temperature is much lower than the critical temperature for blow off (T c ∼ 5000 K for H and 10,000 K for H 2 on Earth). And only particles in the high energy tail of the Maxwellian distribution function of the atmospheric gas, having kinetic energies above the escape energy at the exobase, can overcome this energy barrier ("evaporate") and leave the gravitational field of the planet (e.g., Jeans 1925;Chamberlain 1963;Öpik 1963;Gross 1972).…”

Section: Early Earthmentioning

confidence: 99%

A Comparative Study of the Influence of the Active Young Sun on the Early Atmospheres of Earth, Venus, and Mars

et al. 2007

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Because the solar radiation and particle environment plays a major role in all atmospheric processes such as ionization, dissociation, heating of the upper atmospheres, and thermal and non-thermal atmospheric loss processes, the long-time evolution of planetary atmospheres and their water inventories can only be understood within the context of the evolving Sun. We compare the effect of solar induced X-ray and EUV (XUV) heating on the upper atmospheres of Earth, Venus and Mars since the time when the Sun arrived at the Zero-Age-Main-Sequence (ZAMS) about 4.6 Gyr ago. We apply a diffusive-gravitational equilibrium and thermal balance model for studying heating of the early thermospheres by photodissociation and ionization processes, due to exothermic chemical reactions and cooling by IR-radiating molecules like CO 2 , NO, OH, etc. Our model simulations result in extended thermospheres for early Earth, Venus and Mars. The exospheric temperatures obtained for all the three planets during this time period lead to diffusion-limited hydrodynamic escape of atomic hydrogen and high Jeans' escape rates for heavier species like H 2 , He, C, N, O, etc. The duration of this blow-off phase for atomic hydrogen depends essentially on the mixing ratios of CO 2 , N 2 and H 2 O in the atmospheres and could last from ∼100 to several hundred million years. Furthermore, we study the efficiency of various non-thermal atmospheric loss processes on Venus and Mars and investigate the possible protecting effect of the early martian magnetosphere against solar wind induced ion pick up Yu.N. Kulikov et al. erosion. We find that the early martian magnetic field could decrease the ion-related nonthermal escape rates by a great amount. It is possible that non-magnetized early Mars could have lost its whole atmosphere due to the combined effect of its extended upper atmosphere and a dense solar wind plasma flow of the young Sun during about 200 Myr after the Sun arrived at the ZAMS. Depending on the solar wind parameters, our model simulations for early Venus show that ion pick up by strong solar wind from a non-magnetized planet could erode up to an equivalent amount of ∼250 bar of O + ions during the first several hundred million years. This accumulated loss corresponds to an equivalent mass of ∼1 terrestrial ocean (TO (1 TO ∼1.39 × 10 24 g or expressed as partial pressure, about 265 bar, which corresponds to ∼2900 m average depth)). Finally, we discuss and compare our findings with the results of preceding studies.

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“…Atmospheres with hydrogen, methane, nitrogen, and neon as major constituents, in turn, were studied. Exospheric temperatures were computed and compared with the so-called 'escape or blowoff temperature,' which Gross [1972] defined as the temperature at which Opik's equality criterion is satisfied for each of the constituents and for the radius of the planetary body (Titan in this case). When the exospheric temperature exceeds the blowoff temperature, dynamic outflow is indicated.…”

Section: Mcgovern [1971] Has Made More Detailed Studies Of Atmospherementioning

confidence: 99%

The atmosphere of Titan

Gross¹

1974

Reviews of Geophysics

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Titan, a satellite of Saturn, is unique in that it is the only satellite in the solar system with an extensive atmosphere, possibly more massive than that of the earth. Methane and hydrogen have been discovered, and a greenhouse effect is apparent from infrared measurements. It may be enshrouded by clouds, and this intriguing body may, in time, provide clues to the evolution of the major planets and their satellites. At present, interpretation of the observational evidence concerning the properties of Titan is somewhat speculative and controversial. The status of the observations and theoretical studies is assessed.

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On the Exospheric Temperature of Hydrogen-Dominated Planetary Atmospheres

Cited by 43 publications

References 0 publications

The effect of tidal locking on the magnetospheric and atmospheric evolution of “Hot Jupiters”

The effect of tidal locking on the magnetospheric and atmospheric evolution of “Hot Jupiters”

A Comparative Study of the Influence of the Active Young Sun on the Early Atmospheres of Earth, Venus, and Mars

The atmosphere of Titan

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