James Webb space telescope discovers traces of water vapor on super-hot exoplanet

June 3, 2023  12:11

The James Webb Space Telescope (JWST) has made a remarkable discovery, detecting signs of water vapor in the atmosphere of a scorching gas giant exoplanet that completes an orbit around its star in less than a day. The exoplanet in question, known as WASP-18 b, is a gas giant roughly ten times the mass of Jupiter, the largest planet in our solar system.

WASP-18 b orbits a sun-like star called WASP-18, situated approximately 400 light-years away from Earth. Astonishingly, the planet maintains an average distance of just 1.9 million miles (3.1 million kilometers) from its star, while for comparison, Mercury, the closest planet to the Sun in our solar system, orbits at a distance of 39.4 million miles (63.4 million km), Space.com reports.

Due to the planet's extremely close proximity to its parent star, the temperatures in WASP-18 b's atmosphere reach such intense levels that most water molecules disintegrate, according to NASA. Therefore, the fact that the JWST was able to detect residual water signatures is a testament to the telescope's remarkable observational capabilities. NASA stated, "The spectrum of the planet’s atmosphere clearly shows multiple small but precisely measured water features, present despite the extreme temperatures of almost 5,000 degrees Fahrenheit (2,700 degrees Celsius). It’s so hot that it would tear most water molecules apart, so still seeing its presence speaks to Webb’s extraordinary sensitivity to detect remaining water."

Discovered in 2008, WASP-18 b has been extensively studied by other telescopes such as the Hubble Space Telescope, NASA's X-ray space telescope Chandra, the Transiting Exoplanet Survey Satellite (TESS), and the now-retired infrared Spitzer Space Telescope. However, none of these instruments possessed the sensitivity required to identify water signatures within the planet's atmosphere. Anjali Piette, a postdoctoral fellow at the Carnegie Institution for Science and one of the authors of the new research, expressed her excitement, saying, "Because the water features in this spectrum are so subtle, they were difficult to identify in previous observations. That made it really exciting to finally see water features with these JWST observations."

WASP-18 b 1 .JPG (38 KB)

In addition to its tremendous mass, scorching temperatures, and close proximity to its star, WASP-18 b is also tidally locked, meaning one side of the planet is permanently facing the star, similar to the relationship between the moon and the Earth. Consequently, significant temperature variations exist across the planet's surface. The JWST measurements allowed scientists to map these temperature differences in detail for the first time.

Surprisingly, the data revealed that the most intensely illuminated regions of the planet can be up to 2,000 degrees F (1,100 degrees C) hotter than those in the twilight zone. These substantial temperature differences were unexpected, leading scientists to suspect the presence of an, as yet, unknown mechanism that prevents heat from distributing evenly around the planet. Ryan Challener, a co-author from the University of Michigan, proposed one possible explanation, stating, "The brightness map of WASP-18 b shows a lack of east-west winds that is best matched by models with atmospheric drag. One possible explanation is that this planet has a strong magnetic field, which would be an exciting discovery!"

To generate the temperature map, the researchers measured the infrared glow emitted by the planet by observing the variation in the glow of the parent star as the planet transited in front of and behind the star's disk. Megan Mansfield, a Sagan Fellow at the University of Arizona and one of the authors of the study, expressed her enthusiasm for the JW

Researchers employed a novel approach to construct a temperature map of WASP-18 b, the scorching gas giant exoplanet, using the James Webb Space Telescope (JWST). By observing the variation in the glow of the parent star as the planet passed in front and behind its disk, the team calculated the planet's infrared emission. This groundbreaking technique allowed for the creation of a highly detailed temperature map, providing valuable insights into the planetary dynamics.

Megan Mansfield, a Sagan Fellow at the University of Arizona and one of the authors of the research paper, expressed the significance of the JWST's capabilities, stating, "JWST is giving us the sensitivity to make much more detailed maps of hot giant planets like WASP-18 b than ever before. This is the first time a planet has been mapped with JWST, and it’s really exciting to see that some of what our models predicted, such as a sharp drop in temperature away from the point on the planet directly facing the star, is actually seen in the data."

The study, which sheds light on the temperature variations and atmospheric properties of WASP-18 b, was published online in the prestigious journal Nature on Wednesday, May 31. This significant achievement marks a crucial step forward in our understanding of the complexities of exoplanetary systems.

  • Archive