An international group of scientists using NASA’s Hubble Space Telescope has produced a global weather map of a hot-Jupiter exoplanet called WASP-43b, providing information about temperatures at different layers of the planet’s atmosphere and the amount and distribution of water it contains.
In this illustration the hot-Jupiter WASP-43b orbits its parent star in one of the closest orbits ever measured for an exoplanet of its size – with a year lasting about 19 hours. The color scale on the planet represents the temperature across its atmosphere. Image credit: NASA / ESA / Z. Levay, STScI.
First discovered in 2011, WASP-43b is an exoplanet the size of Jupiter but with double the mass.
The planet is located in the constellation Sextans, about 260 light-years away.
It lies so close to its host star – the orange dwarf star WASP-43 – that it completes an orbit in just 19.5 hours.
It is also gravitationally locked so that it keeps one hemisphere facing the star.
WASP-43b is too distant to be photographed, but because its orbit is observed edge-on to Earth, scientists detected it by observing regular dips in the light of its parent star as the planet passes in front of it.
Now, the astronomers have combined two methods of analyzing exoplanets and put them together in one to study the planet’s atmosphere.
Spectroscopy allowed them to determine the water abundance and temperature structure of the atmosphere.
By observing the planet’s rotation, they were also able to measure the water abundances and temperatures at different longitudes.
“Our observations are the first of their kind in terms of providing a two-dimensional map on the longitude and altitude of the planet’s thermal structure that can be used to constrain atmospheric circulation and dynamical models for hot exoplanets,” said Dr Kevin Stevenson, a team member and an astrophysicist with the University of Chicago.
The Hubble observations show that WASP-43b has winds that howl at the speed of sound from a day side that is hot enough to melt iron – soaring above 1,500 degrees Celsius – to the pitch-black night side that sees temperatures plunge to a comparatively cool 500 degrees Celsius.
“The planet is so hot that all the water in its atmosphere is vaporized, rather than condensed into icy clouds like on Jupiter,” said team member Dr Laura Kreidberg of the University of Chicago.
The amount of water in the giant planets of our Solar System is poorly known because water that has precipitated out of the upper atmospheres of cool gas giant planets like Jupiter is locked away as ice. But on hot Jupiters water is in a vapor that can be readily traced.
“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,” said team member Dr Jonathan Fortney of the University of California, Santa Cruz.
“Space probes have not been able to penetrate deep enough into Jupiter’s atmosphere to obtain a clear measurement of its water abundance. But this giant planet is different. WASP-43b’s water is in the form of a vapor that can be much more easily traced. So we could not only find it, we were able to directly measure how much there is and test for variations along the planet’s longitude,” said team member Dr Derek Homeier of the École Normale Supérieure de Lyon, France.
The scientists found that WASP-43b has about the same amount of water as we would expect for an object with the same chemical composition as our Sun, shedding light on the fundamentals about how the planet formed.
“Next, we aim to make water-abundance measurements for different planets to explore their chemical abundances and learn more about how planets of different sizes and types come to form around our own Sun and the stars beyond it,” Dr Kreidberg said.
The findings are presented in two new papers published online in the journal Science and the Astrophysical Journal Letters.
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Kevin B. Stevenson et al. Thermal structure of an exoplanet atmosphere from phase-resolved emission spectroscopy. Science, published online October 09, 2014; doi: 10.1126/science.1256758
Laura Kreidberg et al. 2014. A Precise Water Abundance Measurement for the Hot Jupiter WASP-43b. ApJ 793, L27; doi: 10.1088/2041-8205/793/2/L27
