It’s Hot Enough on This Exoplanet to Melt Steel

By Steve Koppes, University of Chicago
October 11, 2014 Updated: October 11, 2014

The most detailed weather map ever made of an exoplanet orbiting another star 260 light-years away from Earth shows a world with daytime temperatures hot enough to melt steel.

Scientists used NASA’s Hubble Space Telescope to make the map that provides information about temperatures at different layers of atmosphere on WASP-43b and traces the amount and distribution of water vapor.

The findings have ramifications for the understanding of atmospheric dynamics and the formation of giant planets like Jupiter, researchers say.

“These measurements have opened the door for a new kind of comparative planetology,” says Jacob Bean, assistant professor in astronomy & astrophysics at the University of Chicago.

“Our observations are the first of their kind in terms of providing a two-dimensional map of the planet’s thermal structure that can be used to constrain atmospheric circulation and dynamical models for hot exoplanets,” says Kevin Stevenson, research associate in astronomy & astrophysics.

The observations show that the planet is no place to call home. It’s a world of extremes, where seething winds howl at the speed of sound from a 3,000-degree-Fahrenheit day side to a pitch-black night side that sees temperatures plunge below a relatively cool 1,000 degrees Fahrenheit.


Time-lapse video of WASP-43b over one planet rotation. The left and right panels display the planet’s emission spectrum and temperature structure, respectively, as a function of orbital phase (similar to planet longitude). The rotating spheres depict temperature maps of WASP-43b at three different altitudes. (K.B. Stevenson/University of Chicago)

The Same Size as Jupiter

As a hot ball of predominantly hydrogen gas, there are no surface features on the planet, such as oceans or continents that can be used to track its rotation. Only the severe temperature difference between the day and night sides can be used by a remote observer to mark the passage of a day on this world.

WASP-43b, first discovered in 2011, is too distant to be photographed, but because its orbit is observed edge-on to Earth, astronomers detected it by observing regular dips in the light of its parent star as the planet passes in front of it.

The planet is about the same size as Jupiter, but is nearly twice as massive. The planet is so close to its orange dwarf host star that it completes an orbit in just 19 hours. The planet is also gravitationally locked so that it keeps one hemisphere facing the star, just as our moon keeps one face toward Earth.

The scientists combined two previous methods of analyzing exoplanets and put them together in one for the first time to study the atmosphere of WASP-43b.

Spectroscopy allowed them to determine the water abundance and temperature structure of the atmosphere. By observing the planet’s rotation, the astronomers were also able to measure the water abundances and temperatures at different longitudes.

Bizarre World

Because there’s no planet with these tortured conditions in our solar system, characterizing the atmosphere of such a bizarre world provides a unique laboratory for better understanding planet formation and planetary physics.

“The planet is so hot that all the water in its atmosphere is vaporized, rather than condensed into icy clouds like on Jupiter,” says Laura Kreidberg, a graduate student in astronomy & astrophysics.

“Water is thought to play an important role in the formation of giant planets, since comet-like bodies bombard young planets, delivering most of the water and other molecules that we can observe,” says Jonathan Fortney, from the University of California, Santa Cruz.

However, the water abundances in the giant planets of our solar system are poorly known because water is locked away as ice that has precipitated out of their upper atmospheres.

But on “hot Jupiters”—that is, large planets like Jupiter that have high surface temperatures because they orbit very close to their stars—water is in a vapor that can be readily traced.

The team didn’t simply detect water in the atmosphere of WASP-43b, but also precisely measured how much of it there is and how it is distributed with longitude, Kreidberg says.

In order to understand how giant planets form, astronomers want to know how enriched they are in different elements. WASP-43b has about the same amount of water as we would expect for an object with the same chemical composition as the Sun—which tells something fundamental about how the planet formed.

For the first time astronomers were able to observe three complete rotations of a planet, which occurred during a span of four days. This was essential to making such a precise measurement according to Jean-Michel Désert of the University of Colorado, Boulder.

The team next aims to make water-abundance measurements for different planets to explore their chemical abundances.

Hubble’s planned successor, the James Webb Space Telescope, will be able to not only measure water abundances, but also the abundances of carbon monoxide, carbon dioxide, ammonia, and methane, depending on the planet’s temperature.

The results are published in two papers, one published online in Science Express and the other published in Astrophysical Journal Letters.

Source: University of Chicago. Republished from Futurity.org under Creative Commons License 3.0.

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