First Weather Report From a Faraway Planet
Astronomers detected signs of weather on a planet known as HAT-P-7 b, which is about 1,045 light years away from Earth. The planet’s winds blow at speeds of thousands of kilometers per hour and its clouds appear to be made of corundum, the same mineral as rubies and sapphires.
Abigail Malate, Staff Illustrator
(Inside Science) -- Earth’s weather ranges from blizzards to sandstorms and more. It’s not the only planet in our solar system with weather, either. Jupiter, for example, has storms large enough to swallow Earth. Now researchers have for the first time detected weather-like patterns on an exoplanet, a world outside the solar system.
This alien weather may involve clouds of the same mineral that rubies and sapphires are made of, and winds up to thousands of kilometers per hour. “This would look stunning,” said study lead author David Armstrong, an astrophysicist at the University of Warwick in Coventry, England.
In the past two decades, astronomers have confirmed the existence of more than 3,400 worlds outside Earth’s solar system , many of which NASA’s Kepler space telescope found. These discoveries have revealed that some exoplanets, such as “hot Jupiters” -- gas giants that orbit their stars closer than Mercury does the sun -- are very different from those seen in Earth’s own solar system.
Scientists are now moving from merely discovering exoplanets to uncovering more details about them. For instance, exoplanets reflect light from their stars, and examining this light can yield insights on the atmospheres and surfaces of these distant worlds.
The scientists focused on HAT-P-7 b, also known as Kepler 2b , a giant planet discovered in 2008 located about 1,045 light years from Earth around a star about 50 percent more massive than the sun. HAT-P-7 b is a hot Jupiter roughly 1.4 times Jupiter’s width and 1.8 times its mass that orbits its star about 10 times closer than Mercury does the sun. Dayside temperatures can reach a scorching 1,925 degrees Celsius, “easily hot enough to melt iron,” Armstrong said.
They examined four years of data that the Kepler spacecraft gathered on fluctuations in HAT-P-7 b’s light. They found the brightest spot on the exoplanet changed position over time, shifting to either side of the point closest to the star on the timescale of tens to hundreds of days. This suggested that clouds on the world that reflected this light moved as wind speeds varied over time.
“These measurements are a stunning example of how planets are really places, complete with variable weather,” said astrophysicist Laura Kreidberg at Harvard University in Cambridge, Massachusetts, who did not take part in this study. “It’s really exciting stuff.”
HAT-P-7 b is tidally locked, which means that one side of the exoplanet always faces its star while the other side faces “the cold of space,” Armstrong said. “This makes the dayside much hotter than the nightside. Strong temperature differences like this cause powerful winds, blowing around the planet in an equatorial jet.” Prior research of hot Jupiters suggest that the winds on HAT-P-7 b may blow at speeds of several kilometers per second, he added.
Since the nightside on HAT-P-7 b is cooler than its dayside, clouds form more easily there. However, whereas the clouds on Earth are made of water, those on HAT-P-7 b are made “of condensed minerals, such as corundum or perovskite,” Armstrong said. (Corundum is the mineral that forms rubies and sapphires.)
The exoplanet’s strong winds push these clouds from the nightside onto the dayside, explaining the fluctuations in brightness the researchers detected. “There would be a huge bank of clouds streaming into the bright side of the planet, reaching further when the winds are strongest,” Armstrong said.
Armstrong said they chose HAT-P-7 b because it is one of only a handful of exoplanets that have large bodies of data on the light they reflect from their stars. “HAT-P-7 b is the planet with the second strongest signal available,” he said. “We did look at the strongest, Kepler-13 b, but did not find anything.”
The variable nature of HAT-P-7 b’s weather may be due to magnetic fields , said astrophysicist Vivien Parmentier at the University of Arizona at Tucson, who did not participate in this study. The winds are likely full of electrically charged ions, and the exoplanet’s magnetic fields might drive them back and forth across the planet, he said. “The magnetic explanation seems possible but needs to be confirmed by more theoretical work and observations,” Parmentier said.
Planned space telescopes such as NASA’s James Webb Space Telescope and the European Space Agency’s PLATO or CHEOPS could help shed more light on alien weather, Armstrong said. “Future missions will allow us to start seeing what the full range of exoplanet weather could be,” Armstrong said. “We see huge diversity in the planets we find, so we would expect the same diversity in their atmospheres and weather.”
The scientists detailed their findings online Dec. 12 in the journal Nature Astronomy.
