An artist's illustration of an exoplanet ocean world. Depositphotos.

Webb finds traces of water on a planet 400 light-years away

In a significant scientific breakthrough, astronomers have made an astonishing discovery in their relentless quest to unravel the mysteries of the universe. Using the remarkable capabilities of the James Webb Space Telescope, researchers have identified the presence of water vapor in the atmosphere of an exoplanet known as WASP-18 b.


In a breakthrough study, astronomers have discovered water vapor in the atmosphere of an alien planet, WASP-18 b. Additionally, the team mapped the temperature changes as the planet disappeared behind and emerged from its star. This phenomenon called a secondary eclipse, allows scientists to examine the combined light of the star and the planet. They then fine-tune the measurements using only the star’s light when the planet slips behind it. The discovery was made possible thanks to the James Webb Space Telescope, which continues to amaze us with its potential to explore the cosmos.

Facing the Star: WASP-18 b’s Tidal Locking

Interestingly, WASP-18 b’s “dayside” consistently faces its star, a process known as tidal locking. Akin to how the Moon’s one side constantly faces the Earth, the brightness map of WASP-18 b indicates a significant temperature variation, as high as 1,000 degrees, between its hottest point facing the star and the terminator – the zone where the planet’s day and night sides converge in permanent twilight.


“The sensitivity that the JWST provides enables us to create detailed maps of hot giant planets like WASP-18 b,” stated Megan Mansfield, a Sagan Fellow at the University of Arizona and one of the paper’s authors. This marks the first time a planet has been mapped using the JWST, resulting in intriguing findings, such as the observed steep drop in temperature from the point directly facing the star.

Webb Finds Traces of Water

The team traced temperature gradients across the planet’s dayside. The planet’s cooler temperature at the terminator suggests a factor obstructing the winds from effectively dispersing heat to the night side, though the precise nature of this obstruction remains unknown.

According to co-author Ryan Challener from the University of Michigan, the brightness map indicates a lack of east-west winds. This finding aligns best with models suggesting atmospheric drag. He proposed that WASP-18 b could possess a strong magnetic field, a discovery that would be noteworthy.

One possible interpretation of these findings is that the planet’s magnetic effects cause the winds to blow from the equator over the poles, rather than in an east-west direction as would typically be expected.


James Webb: Water Vapor Presence Despite Extreme Temperatures

The research team observed temperature changes across different atmospheric layers of this gas giant. Temperature elevations were noted to increase by several hundred degrees. Despite the extreme temperature of nearly 2,700 degrees Celsius, which could dismantle most water molecules, Webb’s exceptional sensitivity detected the presence of water vapor in WASP-18 b’s atmosphere.

Louis-Philippe Coulombe, a Ph.D. student at the Université de Montréal and the paper’s lead author, expressed delight at the discovery of the water’s signature in WASP-18 b’s spectrum. Björn Benneke, a UdeM Professor and Coulombe’s Ph.D. advisor, emphasized that these measurements will facilitate the detection of such molecules in a wide range of planets in the future.

Exploring WASP-18 b with JWST and Unraveling Its Origins

The astronomers studied WASP-18 b for approximately six hours using the Near-Infrared Imager and Slitless Spectrograph (NIRISS), a device contributed by several partners, including the Canadian Space Agency, Université de Montréal, and iREx.

Anjali Piette, a postdoctoral fellow at the Carnegie Institution for Science, noted that the water features in the planet’s spectrum were subtle and challenging to identify in earlier observations, making their recent discovery all the more thrilling.

Transiting Exoplanet Community Early Release Science Program

These observations, led by astronomer Natalie Batalha, were part of the Transiting Exoplanet Community Early Release Science Program. Much of this pioneering work was accomplished by early career scientists, including Coulombe, Challener, Piette, and Mansfield.


WASP-18 b’s proximity to its star and Earth and its large mass makes it an interesting research subject. As one of the most massive worlds with atmospheres open to investigation, understanding WASP-18 b may help scientists unravel how such planets form and evolve in their respective systems.

Coulombe concluded, “By analyzing WASP-18 b’s spectrum, we learn about the various molecules in its atmosphere and its formation. Our observations suggest WASP-18 b’s composition resembles its star, implying it formed from the remaining gas post the star’s birth. These findings are invaluable in understanding how unique planets like WASP-18 b, which have no counterpart in our Solar System, come to be.”

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Written by Ivan Petricevic

I've been writing passionately about ancient civilizations, history, alien life, and various other subjects for more than eight years. You may have seen me appear on Discovery Channel's What On Earth series, History Channel's Ancient Aliens, and Gaia's Ancient Civilizations among others.

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