Exoplanet Discovery Alert: Webb Space Telescope Finds Water in Ultra-Hot Alien World

Scientists utilizing the James Webb Space Telescope have made a significant discovery on the exoplanet WASP-18 b, a gas giant roughly 10 times the size of Jupiter, located 400 light-years away. This intriguing world, with an orbital period of just 23 hours, exhibits extreme temperatures of up to 5,000 degrees Fahrenheit (2,700 °C). Employing the capabilities of the Webb Telescope, researchers have generated the first detailed temperature map of WASP-18 b and identified the presence of water vapor within its scorching atmosphere. These findings shed light on the planet’s formation, suggesting it emerged from residual gas after its host star’s birth.

WASP-18 b has captivated astronomers since its discovery in 2009. It stands out as a unique celestial body within our solar system, with no comparable counterpart. Over the years, NASA’s Hubble, Chandra, TESS, and Spitzer space telescopes, along with ground-based observatories, have extensively observed this ultra-hot gas giant, ten times the mass of Jupiter. The recent addition of the James Webb Space Telescope has unveiled new frontiers of knowledge.

The remarkable revelation includes the identification of water vapor in the atmosphere of WASP-18 b. Scientists constructed a temperature map of the planet as it underwent a secondary eclipse, moving behind and reemerging from its star. By analyzing the combined light emitted by the star and planet, researchers refined their measurements by isolating the light emitted solely by the star during the planet’s transit.

Due to tidal locking, the same side of WASP-18 b always faces its star, analogous to the Moon’s relationship with Earth. The temperature map highlights a drastic temperature contrast of up to 1,000 degrees between the hottest point directly facing the star and the terminator, where the day and night sides meet in a perpetual twilight.

The team also developed a brightness map, tracing the glow from the planet’s hot regions as it passed behind and emerged from its star during the secondary eclipse. This allowed scientists to measure the combined light from the star and planet, as well as the light solely from the star as the planet moved behind it. The resulting light curve provides insights into the measured change in the star’s brightness as the planet transits.

Megan Mansfield, a Sagan Fellow at the University of Arizona and co-author of the research paper, expressed enthusiasm about the capabilities of the James Webb Space Telescope: “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 is actually seen in the data, such as a sharp drop in temperature away from the point on the planet directly facing the star.”

The temperature gradient across the day side of the planet was mapped by the team, revealing intriguing insights. The substantial temperature drop near the terminator suggests the presence of a mechanism hindering efficient heat redistribution from the day side to the night side. The exact nature of this phenomenon remains a mystery.

The brightness map of WASP-18 b exhibits a notable absence of east-west winds, consistent with atmospheric drag models. One possible explanation proposed by co-author Ryan Challener from the University of Michigan is the presence of a strong magnetic field, which would represent an exciting discovery.

To obtain the thermal emission spectrum of WASP-18 b, the researchers measured the emitted light across the NIRISS SOSS wavelength range (0.85-2.8 um) of the James Webb Space Telescope. This range captured approximately 65% of the planet’s total energy emission. Despite the extreme temperatures that would typically break apart water molecules, the observations directly confirmed the presence of water vapor in relatively small quantities, showcasing the extraordinary sensitivity of the Webb Telescope.

Louis-Philippe Coulombe, lead author of the study and a graduate student at the University of Montreal, expressed excitement about the detection: “It was a great feeling to look at WASP-18 b’s JWST spectrum for the first time and see the subtle but precisely measured signature of water. Using such measurements, we will be able to detect such molecules for a wide range of planets in the years to come!”

The researchers also examined the planet’s star before, during, and after the planetary eclipse using the James Webb Space Telescope. This allowed them to measure the changes in light during the planet’s passage behind the star, providing insights into the planet’s brightness. By analyzing these measurements, scientists constructed a temperature map of the planet’s day side, indicating temperatures ranging from 2,800 to 4,800 degrees Fahrenheit (1,500 to 2,600 degrees Celsius).

The discovery of water vapor and the subsequent temperature mapping of WASP-18 b represents a collaborative effort involving over 100 scientists worldwide. Natalie Batalha, an astronomer at the University of California, Santa Cruz, led the Transiting Exoplanet Community Early Release Science Program, which coordinated this groundbreaking research. Early career scientists, such as Coulombe, Challener, Piette, and Mansfield, played pivotal roles in this endeavor.

The proximity of WASP-18 b to its star and to us contributes to its status as an intriguing target for scientific investigation, along with its substantial mass. This discovery provides valuable insights into the formation of such planets and their unique characteristics, as Coulombe explained: “By analyzing WASP-18 b’s spectrum, we not only learn about the various molecules that can be found in its atmosphere but also about the way it formed. Those results are very valuable to get a clear picture of how strange planets like WASP-18 b, which have no counterpart in our solar system, come to exist.”

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More about Exoplanet Discovery

• NASA’s James Webb Space Telescope – Official website providing information about the James Webb Space Telescope and its mission.
• WASP-18 b: A Hot Jupiter Transiting the Bright Host Star HD 10069 – Overview of the exoplanet WASP-18 b on NASA’s Exoplanet Archive.
• James Webb Space Telescope: An Overview – NASA’s overview of the James Webb Space Telescope, including its scientific goals and capabilities.
• Water Vapor Detected on the Ultra-Hot Exoplanet WASP-18 b – Research paper published in The Astrophysical Journal Letters describing the discovery of water vapor on WASP-18 b.
• Transiting Exoplanet Community Early Release Science Program – Information about the Transiting Exoplanet Community Early Release Science Program, which coordinated the research on WASP-18 b.