Scientists using the Hubble Space Telescope have developed the most detailed weather map ever of an exoplanet. This map gives information regarding its atmosphere, including air temperature and water vapor content. The research was led by Derek Homeier of the Université de Lyon. Two papers have described this work, one regarding the water vapor content published in Astrophysical Journal Letters, and the other describing the thermal map in Science Express.
The planet, WASP-43b, is a "hot Jupiter" located about 260 light-years away in the constellation Sextans. WASP-43b is twice as dense as Jupiter, though they are roughly the same size. It takes a mere 19 hours to orbit its parent star. The weather on the planet is quite extreme, with temperatures exceeding 3,000 degrees Fahrenheit (1,650 degrees Celsius) during the day and bottoming out below 1,000 degrees Fahrenheit (537 degrees Celsius) at night. Understanding these atmospheric temperature changes and water vapor content gives the researchers clues about the planet’s formation and evolution.
“Our observations are the first of their kind in terms of providing a two-dimensional map of the planet’s thermal structure,” Kevin Stevenson said in a press release. “These maps can be used to constrain circulation models that predict how heat is transported from an exoplanet's hot day side to its cool night side.” Stevenson, of the University of Chicago, was lead author on the Science Express paper.
WASP-43b is tidally locked to the star, just as our moon is to Earth. In order to determine the planet’s position, the team tracked the drastic temperature differences as the planet orbited the star. Analyzing the light that had been filtered through the planet’s atmosphere allowed the team to determine how the water vapor content differed at various latitudes. This emission spectroscopy technique was repeated several times during the orbit in order to account for temperature differences and create an accurate map.
“We have been able to observe three complete rotations — three years for this distant planet — during a span of just four days,” explained Jacob Bean of the University of Chicago, who was a co-author on both papers. “This was essential in allowing us to create the first full temperature map for an exoplanet and to probe its atmosphere to find out which elements it held and where.”
Understanding atmospheric conditions on WASP-43b gives astronomers the unique ability to explore how planets like this are formed and the role water played in that. Much of the water was delivered in the planet’s youth from impacts with comets. Because of the proximity to its star, temperatures are high enough for the water to exist as vapor, which cannot be done with gas planets in our solar system because they are too distant and too cold.
“The planet is so hot that all the water in its atmosphere is vaporized, rather than condensed into the icy clouds we find on Jupiter,” explained Laura Kreidberg of the University of Chicago and lead author of the paper that appeared in Astrophysical Journal Letters.
The team plans to continue their research by using the same techniques used on WASP-43b on other exoplanets in order to understand the water vapor content and identify other elements within the atmosphere.
Kreidberg created this video explaining the discoveries made about the weather on WASP-43b: