Astronomers discover the first cloudless planet resembling Jupiter

Astronomers at the Center for Astrophysics | Harvard & Smithsonian have detected the first Jupiter-like planet without clouds or haze in its observable atmosphere. The results were published this month in the Letters from the Astrophysical Journal.

Named WASP-62b, the gas giant was first detected in 2012 thanks to the Wide Angle Search of Planets (WASP) South. Its atmosphere, however, had never been studied closely until now.

“For my thesis, I worked on the characterization of exoplanets,” says Munazza Alam, a graduate student at the Center for Astrophysics who led the study. “I take discovered planets and follow them to characterize their atmospheres.”

Known as “Hot Jupiter,” WASP-62b is 575 light years away and about half the mass of Jupiter in our solar system. However, unlike our Jupiter, which takes nearly 12 years to orbit the sun, WASP-62b rotates around its star in just four and a half days. This proximity to the star makes it extremely hot, hence the name “hot Jupiter”.

Using the Hubble Space Telescope, Alam recorded data and observations of the planet using spectroscopy, the study of electromagnetic radiation to help detect chemical elements. Alam specifically monitored WASP-62b as it scanned three times in front of its host star, making visible light observations, which can detect the presence of sodium and potassium in a planet’s atmosphere.

“I admit that at first I wasn’t too excited about this planet,” Alam says. “But once I started taking a look at the data, I got excited.”

Although there is no evidence for potassium, the presence of sodium was remarkably clear. The team was able to see the full sodium absorption lines in their data, or their full fingerprint. Clouds or haze in the atmosphere would obscure sodium’s full signature, Alam says, and astronomers can usually only distinguish small clues to its presence.

“It’s irrefutable proof that we see a clear atmosphere,” she says.

Cloudless planets are extremely rare; Astronomers estimate that less than 7% of exoplanets have a clear atmosphere, according to recent research. For example, the first and only other known exoplanet with a clear atmosphere was discovered in 2018. Named WASP-96b, it is classified as Hot Saturn.

Astronomers believe that studying exoplanets with cloudless atmospheres can lead to a better understanding of how they formed. Their rarity “suggests that something else is going on or that they formed in a different way than most planets,” Alam says. Clear atmospheres also make it easier to study the chemical makeup of planets, which can help identify what a planet is made of.

With the launch of the James Webb Space Telescope later this year, the team hopes to have new opportunities to study and better understand WASP-62b. The telescope’s improved technologies, like higher resolution and better accuracy, should help them probe the atmosphere even closer to look for the presence of more elements, like silicon.