Astronomers have just completed the first successful measurement of the spectrum of the night side of an exoplanet in the WASP-121 system located 850 light years from Earth. The host star is a magnitude 11 yellow-dwarf, or G-type star, similar to the Sun, Alpha Centauri A, Tau Ceti, and 51 Pegasi. The exoplanet, WASP -121b, is a football-shaped ultra-hot gas giant neary twice the size of Jupiter, orbiting its host star only a few stellar radii away. “We were very excited to obtain a global view of the water cycle on the exoplanet,” MIT’s Daylan Tansu told The Daily Galaxy about their new Hubble Space Telescope observations.
Violent Tango of Day and Night —Tidal Locked Extremes
The Hubble data unveiled clues to its hellish atmosphere and weather, with metal clouds made up of iron, corundum, and titanium. In millions of years, the whiplashing forces WASP121-b endures from its host star will rip its atmosphere apart. Until then, the planet will continue its extraordinary violent tango of day and night.
The tidally locked WASP-121b is the first exoplanet found to contain water in an extrasolar planetary stratosphere, the layer where clouds condense and become opaque. The WASP-121b completes a revolution in just 1.7 days –only slightly longer than an Earth day. Intense gravitational forces due to its proximity to the host star created the exoplanet’s weird oblong shape.
The most surprising element of the latest findings are the details of the planet’s climate; how its temperatures plummet at night and change throughout the atmosphere. The team observed the hot Jupiter using the Hubble Space Telescope.
“WASP-121b orbits very close to its host star, making its dayside ultra-hot,” Daylan told The Daily Galaxy. “For example, this causes water molecules to dissociate on the day side, which then recombine on the night side. The temperature contrast between the day and night sides also causes strong winds across the planet.”
Very Hot Jupiter’s
“Hot Jupiters are famous for having bright day sides, but the night side is a different beast,” said Tansu Daylan, an astrophysicist and a co-author of the paper: “WASP-121b’s night side is about 10 times fainter than its day side.”
The physics of the vastly different temperatures on either side of the planet make a dynamic environment of its atmosphere: In the daytime, water molecules get ripped apart by the nearly 5,000° Fahrenheit heat and blown to the night side of the planet by 11,000-mile-per-hour winds. “These winds are much faster than our jet stream, and can probably move clouds across the entire planet in about 20 hours,” Daylan said.
On the night side, the hydrogen and oxygen atoms recombine, only to whip around back to the dayside to get split again. It’s much more volatile than Earth’s water cycle of evaporating, condensing, and raining, even when our world is at its most violent.
The planet’s night side is cold enough that it may foster clouds made of metal. Hot temperatures on the planet’s warm side may vaporize iron, corundum, and titanium, which may cause rains of heavy metal back on the cold side when the gaseous clouds whip around. Previously, another hot Jupiter—WASP 76b—showed signs of a similar phenomenon.
Following up on the recent Hubble observations, the team has reserved observation time on the newly launched Webb Space Telescope, which is set to begin its scientific work this summer. (Currently, Webb is still getting set up.) They want to map the planet’s carbon monoxide, which lead author Thomas Mikal-Evans, an astrophysicist at MIT, said could help the researchers understand how hot Jupiters form.
The Last Word
MIT’s Tansu Daylan explained to The Daily Galaxy that … “the measurements collected during this work are sensitive to water. We basically measure the near-infrared spectrum of the planet at all viewing angles and then “infer” the composition and temperature of its upper atmosphere. The James Webb Space Telescope will also observe WASP-121b. These observations will extend the wavelength coverage and allow the carbon content of the atmosphere to be probed, which can reveal where on the protoplanetary disk the planet may have formed.”