Computer Science
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007natur.450..845k&link_type=abstract
Nature, Volume 450, Issue 7171, pp. 845-848 (2007).
Computer Science
20
Scientific paper
Recent observations of the planet HD209458b indicate that it is surrounded by an expanded atmosphere of atomic hydrogen that is escaping hydrodynamically. Theoretically, it has been shown that such escape is possible at least inside an orbit of 0.1AU (refs 4 and 5), and also that H3+ ions play a crucial role in cooling the upper atmosphere. Jupiter's atmosphere is stable, so somewhere between 5 and 0.1AU there must be a crossover between stability and instability. Here we show that there is a sharp breakdown in atmospheric stability between 0.14 and 0.16AU for a Jupiter-like planet orbiting a solar-type star. These results are in contrast to earlier modelling that implied much higher thermospheric temperatures and more significant evaporation farther from the star. (We use a three-dimensional, time-dependent coupled thermosphere-ionosphere model and properly include cooling by H3+ ions, allowing us to model globally the redistribution of heat and changes in molecular composition.) Between 0.2 and 0.16AU cooling by H3+ ions balances heating by the star, but inside 0.16AU molecular hydrogen dissociates thermally, suppressing the formation of H3+ and effectively shutting down that mode of cooling.
Aylward Alan D.
Koskinen Tommi T.
Miller Steve
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