October 13, 2014 – A team of scientists including a University of Colorado Boulder professor used NASA’s Hubble Space Telescope to make the most detailed global map yet of the glow from a turbulent planet outside our solar system, revealing its secrets of air temperatures and water vapor.
The Hubble observations show that the planet, called WASP-43b, is no place to call home. It’s a world of extremes, where winds howl at the speed of sound from a 3,000-degree-Fahrenheit dayside to a pitch-black nightside when temperatures plunge to a relatively cool 1,000 degrees Fahrenheit, still hot enough to melt silver.
Astronomers have mapped the temperatures at different layers of the planet’s atmosphere and traced the amount and distribution of water vapor. The findings have ramifications for the understanding of atmospheric dynamics and how giant planets like Jupiter are formed.
“These measurements have opened the door for a new kinds of ways to compare the properties of different types of planets,” said team leader Jacob Bean of the University of Chicago.
First discovered in 2011, WASP-43b is located 260 light-years away. The planet 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.
As a ball of predominately hot hydrogen gas, there are no surface features on WASP-43b like oceans or continents that can be used to track its rotation, said CU-Boulder Assistant Professor Jean-Michel Désert, second author on the new study. Only the drastic temperature difference between the dayside and nightside can be used by remote observers to mark the passage of a day on the strange, gaseous planet, he said.
“WASP-43b is extreme in many ways,” said Désert. “It’s the size of Jupiter with twice its mass. Its orbit around its host star, called an orange dwarf, takes only about 19 hours – the blink of an eye compared to the 365 days it takes Earth to orbit the sun.”
The planet also is gravitationally locked so that it keeps one hemisphere facing the star, just as our moon keeps one face toward Earth.
This was the first time astronomers were able to observe three complete rotations of any planet, which occurred during a span of four days. Scientists combined two previous methods of analyzing exoplanets in an unprecedented technique to study the atmosphere of WASP-43b. They used spectroscopy, dividing the planet’s light into its component colors, to determine the amount of water and the temperatures of the atmosphere. By observing the planet’s rotation, the astronomers also were able to precisely measure how the water is distributed at different longitudes.
Because there is 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.
“These observations allow us to determine the abundance of water in the planet’s atmosphere, which is a major element involved in planetary formation,” said Désert. “By measuring the composition of this planet, we will have a better idea where it formed within the proto-planetary disk of the host star.”
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 so-called “hot Jupiters,” gas giants that have high surface temperatures because they orbit very close to their stars, water is in a vapor that can be readily traced.
In order to understand how giant planets form astronomers want to know how enriched they are in different elements. The team 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. The team next aims to make water-abundance measurements for different planets.
The results are presented in two new papers, one published online in Science Express October 9 and the other published in The Astrophysical Journal Letters on September 12.
The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA’s Goddard Space Flight Center in Greenbelt, Maryland manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington.