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Planetary Science Astronomy Astrophysics

The Discovery of Cloudless Exoplanet


For detailed atmospheric characterization and precise chemical abundant constraints, cloudless exoplanets with haze-free atmospheres at the pressures, represent a valuable opportunity to be probed by transmission spectroscopy. Measured with Hubble/STIS and Spitzer/IRAC, the first optical to infrared (0.3−5 μm) transmission spectrum of the hot Jupiter WASP-62b. Characterized by a 5.1σ detection of Na; absorption at 0.59 μm; the spectrum is; in which the pressure-broadened wings of Na D-lines are observed from space for the first time. At 0.4 μm, a spectral feature is tentatively attributed to SiH at 2.1σ confidence. Consistent with a cloud-free atmosphere, their retrieval analyses are without significant contamination from stellar heterogeneities. To assess the atmospheric characterization potential of WASP-62b, the team simulated James Webb Space Telescope (JWST) observations, for a combination of instrument modes. Within the scope of its Early Release Science (ERS) program, JWST can conclusively detect Na, H2O, FeH, NH3, CO, CO2, CH4, and SiH, the team demonstrated. WASP-62b could prove a benchmark giant exoplanet for detailed atmospheric characterization in the James Webb era, as it is the only transiting giant planet currently known in the JWST continuous viewing zone.


Hot Jupiter-Like Exoplanet WASP-62b

At Harvard & Smithsonian (the center for astrophysics), astronomers have detected for the second time an exoplanet without clouds or haze in its observable atmosphere. But it’s the first Jupiter-like exoplanet. The findings were published on 11th January 2021, in The Astrophysical Journal Letters.

The gas giant named WASP-62b was first detected in 2012 through the Wide Angle Search for Planets (WASP) South survey. Until now, however, its atmosphere had never been closely studied.

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

WASP-62b: JWST Predictions
WASP-62b: JWST Predictions

With the help of spectroscopy (the study of electromagnetic radiation to help detect chemical elements), Alam (a graduate student at Harvard & Smithsonian who led the study) recorded the data and observations of the planet using the Hubble Space Telescope. Making visible light observations that can detect the presence of sodium and potassium in a planet’s atmosphere, she specifically monitored WASP-62b as it swept in front of its host star three times.

The presence of sodium was strikingly clear, on the other hand, there was no evidence whatsoever that could hint towards the presence of potassium. Clouds or haze in the atmosphere would obscure the complete signature of sodium, but this was not the case, as the team was able to view the full sodium absorption lines in their data or its complete fingerprint and astronomers usually can make out only small hints of its presence.

“This is smoking gun evidence that we are seeing a clear atmosphere.”

Munazza Alam

According to recent research, it is estimated that less than 7 percent of exoplanets have clear atmospheres, thus cloud-free exoplanets are exceedingly rare. For example, Discovered in 2018, an exoplanet named WASP-96b, classified as a “Hot Saturn” is the first and only other exoplanet with a clear atmosphere.

Transmission Spectrum of WASP-96b
Transmission Spectrum of WASP-96b

Studying exoplanets with cloudless atmosphere can lead to a better understanding of how they were formed or so is believed by astronomers. Clear atmospheres also make it easier to study the chemical composition of planets, thus helping in identifying what a planet is made of.

Their rarity “suggests something else is going on or they formed in a different way than most planets.”

James Webb Space Telescope
James Webb Space Telescope


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

Journal Reference:

  1. Munazza K. Alam, Mercedes López-Morales, Ryan J. MacDonald, Nikolay Nikolov, James Kirk, Jayesh M. Goyal, David K. Sing, Hannah R. Wakeford, Alexander D. Rathcke, Drake L. Deming, Jorge Sanz-Forcada, Nikole K. Lewis, Joanna K. Barstow, Thomas Mikal-Evans, Lars A. Buchhave. Evidence of a Clear Atmosphere for WASP-62b: The Only Known Transiting Gas Giant in the JWST Continuous Viewing ZoneThe Astrophysical Journal, 2021; 906 (2): L10 DOI: 10.3847/2041-8213/abd18e


Shivam Taneja

An author, a poet, a traveler, and a space explorer. To unravel the unexplained mysteries of the universe.

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