Exoplanet Weather Forecast: Hot and Nasty

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Alien worlds seem to be as common as the stars they’re orbiting.

Over 500 exoplanets are confirmed to exist, another 1,200 candidates have been flagged by Kepler and one is playing a frustrating game of hide-and-seek. The fun thing is that the more we spot, the more it looks as if there are a preponderance of smaller worlds. If you follow the logic, it shouldn’t be too long until we find a bona fide “Earth-like” world. It is one of the most noble and compelling searches of our time.

Although there are lots out there, it’s notoriously difficult to understand what these worlds are made of and what processes dominate their atmospheres (if, indeed, they have an atmosphere). This is the reason why we need sophisticated means of observing these distant worlds and sophisticated computer models to back up the data.

Enter Kevin Heng from the Institute for Astronomy at ETH Zurich, Switzerland, one such scientist who is hard at work modeling the climates of exoplanets. And he’s hot on the trail of explaining one exoplanet mystery.

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Sunset Scorcher

On analyzing some large Jupiter-like exoplanets, it has become increasingly apparent that something is awry with the temperature profiles of their atmospheres. For example, in Oct. 2010, I reported on a mysterious “hot spot” in the atmosphere of Andromedae b (pictured above).

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As Andromedae b orbits very close to its star, the hottest region in the exoplanet’s atmosphere isn’t on its star-facing side (as would be expected). The hottest region has been shifted 80 degrees away from the star-facing side. This means that if you were floating on the planet’s clouds, with the star directly overhead, that wouldn’t be the hottest location on the planet. Sunset and sunrise, however, would be very toasty. The planet is also “tidally locked” with its star, meaning one side is always facing the star — there is a perpetual day on one side, and a perpetual night on the other.

Although astronomers have speculated that the star’s heat has been transported away from the star-facing side of the exoplanet by its atmosphere, the mechanism isn’t fully understood.

By studying an exoplanet called HD 209458b — another “hot-Jupiter” some 150 light-years from Earth — Heng has produced a complex climatic model of the world’s atmosphere. What’s more, his model explains that the violent planet-wide winds generated by the close proximity to its parent star reproduces these atmospheric “hot spots.”

“The shift occurs because strong winds in the exoplanet’s atmosphere carry part of the heat from the day side to the night side,” Heng said in a recent press release. “The exoplanet is basically trying to reduce the temperature difference between its day and night sides.”

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Perpetual Blowtorch

Now, observations seem to support Heng’s computer simulations. Independent studies have detected violent wind speeds on HD 209458b of around 2 kilometers per second (4,500 miles per hour!). These winds are rapidly transporting the star’s heat toward the night-side of the planet, creating the offset “hot spots.”

This is one exoplanet I’d never want to visit. It sounds like a perpetual planet-wide blowtorch.

Publication: Heng K, et al. Atmospheric circulation of tidally-locked exoplanets: a suite of benchmark tests for dynamical solvers. Mon. Not. R. Astron. Soc., in press (2011) http://arxiv.org/abs/1010.1257

Source: Physorg.com

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