NASA’s James Webb Space Telescope has made a groundbreaking observation of the exoplanet WASP-80 b, capturing spectra that reveal the presence of both methane gas and water vapor in its atmosphere. While water vapor has been previously detected in numerous planets, methane has proven elusive in the atmospheres of transiting exoplanets when studied with space-based spectroscopy.This discovery, made possible by Webb’s advanced capabilities, provides valuable insights into exoplanet atmospheres and marks a significant step forward in our understanding of these distant worlds. Taylor Bell from the Bay Area Environmental Research Institute (BAERI) and Luis Welbanks from Arizona State University delve into the significance of this discovery in their recent publication in the scientific journal Nature.
WASP-80 b, the exoplanet observed by NASA’s James Webb Space Telescope, falls into the category of “warm Jupiter,” characterized by a temperature of approximately 825 kelvins (about 1,025 degrees Fahrenheit). These planets share similarities in size and mass with Jupiter in our solar system but occupy an intermediate temperature range between hot Jupiters and cold Jupiters. WASP-80 b completes an orbit around its red dwarf star every three days and resides 163 light-years away in the constellation Aquila.Due to its proximity to the star and considerable distance from Earth, direct observation of the planet is challenging. Researchers employ the transit and eclipse methods, studying the combined light from the star and planet to glean valuable insights into its atmosphere.
The transit method was employed to observe the WASP-80 b system as the planet traversed in front of its host star, resulting in a subtle dimming of the observed starlight, akin to someone passing in front of a lamp causing a temporary reduction in light. During this phase, the starlit atmosphere along the planet’s day/night boundary was illuminated. Notably, at specific wavelengths where the molecules in the planet’s atmosphere absorb light, the atmosphere appeared denser, leading to a more pronounced dimming compared to wavelengths where the atmosphere appeared more transparent.This technique enables scientists to discern the composition of the planet’s atmosphere by analyzing the colors of light that are being obstructed.
Using the eclipse method, the observation of the WASP-80 b system involved tracking the planet as it moved behind its star from our viewpoint, resulting in another minor reduction in the total received light. All objects emit thermal radiation, and the intensity and color of this emitted light depend on the object’s temperature. In the moments before and after the eclipse, the planet’s hot dayside faces us. By gauging the dip in light during the eclipse, we were able to measure the infrared light emitted by the planet. In eclipse spectra, the absorption by molecules in the planet’s atmosphere typically manifests as a decrease in the planet’s emitted light at specific wavelengths.Given that the planet is significantly smaller and cooler than its host star, the depth of an eclipse is considerably smaller than the depth of a transit.
The spectra of WASP-80 b show clear evidence of absorption by water and methane.
The measured transit spectrum (top) and eclipse spectrum (bottom) of WASP-80 b from NIRCam’s slitless spectroscopy mode on NASA’s James Webb Space Telescope reveal absorption from water and methane, indicated with colored contours. During a transit, when the planet passes in front of the star, molecules in the atmosphere block more light at certain colors, causing a deeper dimming at those wavelengths. In an eclipse, when the planet passes behind the star, molecules absorb some of the planet’s emitted light at specific colors, leading to a smaller dip in brightness compared to a transit.
The initial observations were transformed into a spectrum, a measurement showing how much light is either blocked or emitted by the planet’s atmosphere at different wavelengths. Using different tools and models, scientists confirmed the definitive detection of methane in WASP-80 b’s atmosphere.
The researchers used robust statistical methods to assess the likelihood of their detection being random noise. In their field, a ‘5-sigma detection’ is considered the gold standard, with odds of 1 in 1.7 million for random noise. Surprisingly, they found methane at a 6.1-sigma level in both transit and eclipse spectra, setting the odds of a false detection at 1 in 942 million for each observation, surpassing the 5-sigma gold standard and reinforcing confidence in their detections.
This confident detection allows scientists to explore the chemical composition of the planet, providing insights into its birth, growth, and evolution. For instance, analyzing the methane and water content helps infer the carbon-to-oxygen ratio, offering clues about the planet’s formation location and history. Furthermore, the discovery excites researchers as it opens the door to comparing planets outside our solar system with those within it. Previous NASA missions studied gas giants in our solar system, measuring methane levels.Now, with measurements from an exoplanet, scientists can make an “apples-to-apples” comparison, examining if expectations from our solar system align with observations beyond it.
Looking ahead to future discoveries with the James Webb Space Telescope (Webb), the recent findings on WASP-80 b indicate that more exciting results are on the horizon. With upcoming observations using the MIRI and NIRCam instruments on Webb, scientists plan to explore the properties of WASP-80 b’s atmosphere at various wavelengths of light. This could reveal additional carbon-rich molecules like carbon monoxide and carbon dioxide, providing a more comprehensive understanding of the planet’s atmospheric conditions.
The detection of methane and other gases in exoplanets contributes to expanding our knowledge of how chemistry and physics operate in environments different from Earth. This ongoing exploration may eventually extend to planets resembling our own. The message is clear – the journey of discovery with the James Webb Space Telescope holds the promise of unexpected surprises in the realm of exoplanetary science.