The Upper Atmosphere of HD17156b

Abstract

HD17156b is a newly-found transiting extrasolar giant planet (EGP) that orbits its G-type host star in a highly eccentric orbit (e~0.67) with an orbital semi-major axis of 0.16 AU. Its period, 21.2 Earth days, is the longest among the known transiting planets. The atmosphere of the planet undergoes a 27-fold variation in stellar irradiation during each orbit, making it an interesting subject for atmospheric modelling. We have used a three-dimensional model of the upper atmosphere and ionosphere for extrasolar gas giants in order to simulate the progress of HD17156b along its eccentric orbit. Here we present the results of these simulations and discuss the stability, circulation, and composition in its upper atmosphere. Contrary to the well-known transiting planet HD209458b, we find that the atmosphere of HD17156b is unlikely to escape hydrodynamically at any point along the orbit, even if the upper atmosphere is almost entirely composed of atomic hydrogen and H+, and infrared cooling by H3+ ions is negligible. The nature of the upper atmosphere is sensitive to to the composition of the thermosphere, and in particular to the mixing ratio of H2, as the availability of H2 regulates radiative cooling. In light of different simulations we make specific predictions about the thermosphere-ionosphere system of HD17156b that can potentially be verified by observations.

31 pages, 42 eps figures

References in corpus (11)

• Evolution of the Solar Activity over Time and Effects on Planetary Atmospheres: I. High-energy Irradiances (1-1700 A)
• Detection of oxygen and carbon in the hydrodynamically escaping atmosphere of the extrasolar planet HD209458b
• Roche lobe effects on the atmospheric loss of "Hot Jupiters"
• Atmospheric Escape from Hot Jupiters
• Exoplanet HD 209458b : Evaporation strengthened
• Five Intermediate-Period Planets from the N2K Sample
• HD 17156b: A Transiting Planet with a 21.2 Day Period and an Eccentric Orbit
• Detection of Intermediate-Period Transiting Planets with a Network of Small Telescopes: transitsearch.org
• Parameters and Predictions for the Long-Period Transiting Planet HD 17156b
• Improved parameters for the transiting planet HD 17156b: a high-density giant planet with a very eccentric orbit
• No Detectable H3+ Emission from the Atmospheres of Hot Jupiters

Cited by in corpus (6)

• Disequilibrium Carbon, Oxygen, and Nitrogen Chemistry in the Atmospheres of HD 189733b and HD 209458b
• The escape of heavy atoms from the ionosphere of HD209458b. I. A photochemical-dynamical model of the thermosphere
• Characterizing the thermosphere of HD209458b with UV transit observations
• Thermal escape from extrasolar giant planets
• Finite temperature quantum statistics of H${}_3^{+}$ molecular ion
• Mass loss by atmospheric escape from extremely close-in planets