Breathing methane gas on a distant world

NASA‘s James Webb Space Telescope Methane has been detected in the atmosphere Exoplanet WASP-80 b, a milestone in space exploration. The discovery, confirmed by advanced light analysis methods, sheds light on the planet’s composition and allows comparisons with planets in our solar system.

NASA’s James Webb Space Telescope observed the exoplanet WASP-80 b as it passed in front of and behind its host star, revealing spectra indicating the presence of an atmosphere containing methane and water vapor. While water vapor has been detected on more than a dozen planets so far, methane, a molecule that was abundant in the planet’s atmosphere, was not until recently. Jupiter, Saturn, UranusAnd Neptune Within our solar system – they remained elusive in the atmospheres of transiting exoplanets when studied using space spectroscopy.

Taylor Bell of the Bay Area Environmental Research Institute (BAERI), based at NASA’s Ames Research Center in Silicon Valley, California, and Lewis Wilbanks of Arizona State University, tell us more about the importance of detecting methane in the outer atmospheres of exoplanets, and discuss how it has facilitated observations Web Detecting methane in exoplanet atmospheres. Identification of this long-awaited molecule. These results were recently published in the scientific journal Nature.

Understanding “Warm Jupiter” WASP-80 B

“With a temperature of about 825 K (about 1025 degrees F), WASP-80 b is what scientists call “warm Jupiters,” planets similar in size and mass to Jupiter in our solar system but whose temperature falls in between those of hot Jupiters, such as 1,450 degrees Celsius. K (2,150 °F) HD 209458 b (the first exoplanet to be discovered), and cold Jupiters, like ours, have a temperature of about 125 K (235 °F). WASP-80 b orbits its red dwarf star once every three days, and is located 163 light-years away from us in the constellation Vulture. Since the planet is so close to its star and both are so far away from us, we cannot see the planet directly even with the most advanced telescopes like Webb. Instead, researchers study the combined light from the star and the planet using the transit method (which has been used to discover most known exoplanets) and the eclipse method.

Innovative monitoring technologies

Using the transit method, we observed the system when the planet moved in front of its star from our perspective, causing the starlight we see to dim slightly. It’s as if someone walks past the lamp and the light dims. During this time, the star illuminates a thin ring of the planet’s atmosphere around the planet’s day-night boundary, and at certain colors of light where molecules in the planet’s atmosphere absorb the light, the atmosphere appears thicker and blocks more starlight. This causes deeper opacity compared to other wavelengths where the atmosphere appears transparent. This method helps scientists like us understand the components of a planet’s atmosphere by seeing what colors of light are obscured.

Meanwhile, using the eclipse method, we observed the system as the planet passed behind its star from our perspective, causing another slight decrease in the total light we received. All objects emit some light, called thermal radiation, and the intensity and color of the light emitted depends on how hot the object is. Just before and after the eclipse, the planet’s hot day side is pointed toward us, and by measuring the dip in light during the eclipse, we were able to measure infrared light emanating from the planet. For eclipse spectra, absorption by molecules in a planet’s atmosphere typically appears as a decrease in the light emitted by the planet at specific wavelengths. Also, because the planet is much smaller and cooler than its host star, the depth of the eclipse is much smaller than the depth of the transit.

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. In both spectra, there is clear evidence of absorption from water and methane, whose contributions are indicated by colored lines. During a transit, the planet passes in front of the star, and in the transit spectrum, the presence of particles causes the planet’s atmosphere to block more light at certain colors, causing deeper dimming at those wavelengths. During an eclipse, the planet passes behind the star, and in this eclipse spectrum, particles absorb some of the light emitted by the planet in specific colors, resulting in a smaller drop in brightness during an eclipse than during a transit. Image credit: PAYRI/NASA/Taylor Bell

Spectral data analysis

Our initial observations had to be converted into something we call a spectrum; This is basically a measurement that shows how much light is blocked or emitted by a planet’s atmosphere with different colors (or wavelengths) of light. Many different tools exist for converting raw observations into useful spectra, so we used two different methods to ensure that our results were robust to different assumptions. We then interpreted this spectrum using two types of models to simulate what the planet’s atmosphere would look like under these extreme conditions. The first type of model is quite flexible, experimenting with millions of combinations of methane, water abundances and temperatures to find the combination that best matches our data. The second type, called “self-consistent models,” also explores millions of combinations, but uses our existing knowledge of physics and chemistry to determine the levels of methane and water to expect. Both types of models reach the same conclusion: eventual detection of methane.

To validate our findings, we used robust statistical methods to evaluate the likelihood that our finding was random noise. In our field, we consider the “gold standard” to be so-called “5 sigma detection,” which means that the odds of detection resulting from random noise are 1 in 1.7 million. At the same time, we detected methane at 6.1 sigma in both the transit and eclipse spectrum, setting the odds of a false discovery in each observation at 1 in 942 million, exceeding the “gold standard” of 5 sigma, and enhancing our confidence in both. Discoveries.

Implications for methane detection

With this confident discovery, not only have we found an elusive molecule, but we can now begin to explore what this chemical structure tells us about the birth, growth and evolution of the planet. For example, by measuring the amount of methane and water in the planet, we can deduce the ratio of carbon atoms to oxygen atoms. This ratio is expected to change depending on where and when planets form in their system. Thus, examining the carbon-to-oxygen ratio can provide clues about whether the planet formed near or far away from its star before gradually moving inward.

Another thing that excited us about this discovery was the opportunity to finally compare planets outside our solar system with planets inside it. NASA has a history of sending spacecraft to the gas giants of our solar system to measure the amount of methane and other molecules in their atmosphere. Now, by measuring the same gas in an exoplanet, we can start to make an “apples-to-apples” comparison and see if the predictions from the solar system match what we see outside it.

Future prospects with the James Webb Space Telescope

Finally, as we look forward to future discoveries with Webb, this result shows us that we are on the verge of even more exciting discoveries. Additional MIRI and NIRCam observations of WASP-80 b using Webb will allow us to explore the properties of the atmosphere at different wavelengths of light. Our findings lead us to believe that we will be able to monitor other carbon-rich molecules such as carbon monoxide and carbon dioxide, enabling us to paint a more comprehensive picture of the conditions prevailing in this planet’s atmosphere.

In addition, when we find methane and other gases on exoplanets, we will continue to expand our knowledge about how chemistry and physics work under conditions different from those on Earth and, perhaps soon, on other planets reminiscent of what we have here. at home. One thing is clear: a voyage of exploration with the James Webb Space Telescope is full of potential surprises.

Reference: “Methane throughout the atmosphere of the warm exoplanet WASP-80b” by Taylor J. Bell, Lewis Wilbanks, Everett Schloein, Michael R. Lane, Jonathan J. Fortney, Thomas B. Green, Kazumasa Ono, Vivian Parmentier, Emily Rauscher, Thomas J. . Beattie, Sajnik Mukherjee, Lindsay S. Weiser, Martha L. Boyer, Marcia J. Ricky and John A. Stansbury, November 22, 2023, nature.
doi: 10.1038/s41586-023-06687-0

About the authors:

• Taylor Bell is a postdoctoral research scientist at the Bay Area Environmental Research Institute (BAERI), working at NASA Ames Research Center in Silicon Valley, California.
• Lewis Wilbanks is a NASA Hubble Fellow at Arizona State University in Tempe, Arizona.