A transmission spectrum taken from a single observation using the Webb Near-Infrared Imager and Slitless Spectrograph (NIRISS) reveals the atmospheric characteristics of the hot-gas exoplanet WASP-96 b. The transmission spectrum is made by comparing starlight filtered through the planet’s atmosphere as it moves through the star with the unfiltered starlight detected when the planet is next to the star. Each of the 141 data points (white circles) in this graph represents the amount of light of a particular wavelength that is blocked by the planet and absorbed by its atmosphere. Courtesy: NASA, ESA, CSA, ST
Webb’s Giant Mirror and precision instruments join forces to capture the most detailed spectrum of an exoplanet’s atmosphere ever
In a remarkable exoplanet dream come true, NASA’s James Webb Space Telescope has demonstrated its unprecedented capacity to analyze the atmosphere of an exoplanet more than 1,000 light-years away. With the combined forces of its 270-square-foot (25-square-meter) mirror, precision spectrographs, and sensitive detectors, Webb found—in a single observation—the unmistakable signature of water, indications of fog, and evidence of clouds that were thought not to exist. based on previous observations. The transmission spectrum of the hot gas giant WASP-96 b taken with Webb’s Near-Infrared Imager and Slitless Spectrograph (NIRISS) offers just a glimpse into Webb’s exciting future for exoplanet research.
A light curve from Webb’s Near-Infrared Imager and Slitless Spectrograph (NIRISS) shows the change in brightness of the light from the WASP-96 star system over time as the planet transits the star. A transit occurs when an orbiting planet moves between the star and the telescope, blocking some of the light from the star. This observation was made using NIRISS’s slit-free spectroscopy (SOSS) mode, which involves capturing the spectrum of a single bright object, such as the star WASP-96, in a field of view. To capture this data, Webb stared at the WASP-96 star system for 6 hours and 23 minutes, starting about 2½ hours before the pass and ending about 1½ hours after the pass was complete. The crossing itself lasted just under 2 and a half hours. The curve includes a total of 280 separate brightness measurements – one every 1.4 minutes. Courtesy: NASA, ESA, CSA, STScI
Webb reveals steamy atmosphere of distant exoplanet in exquisite detail
NASA’s James Webb Space Telescope has captured the distinct signature of water in the atmosphere around a hot, bloated gas giant planet orbiting a distant Sun-like star. He also found evidence of clouds and fog.
The observation is the most detailed of its kind to date, demonstrating Webb’s incredible ability to analyze atmospheres hundreds of light years away. It reveals the presence of specific gas molecules based on small decreases in the brightness of precise colors of light.
Over the past two decades, the Hubble Space Telescope has analyzed numerous exoplanet atmospheres, capturing the first clear detection of water in 2013. However, Webb’s immediate and more detailed observation marks a giant leap forward in the quest to characterize potentially habitable planets beyond Earth.
WASP-96 b is one of more than 5,000 confirmed exoplanets in the Milky Way. Located approximately 1,150 light-years away in the constellation Phoenix in the southern sky, it is a type of gas giant that has no direct counterpart in our solar system. With a mass less than half that of Jupiter and a diameter 1.2 times larger, WASP-96 b is far fluffier than any planet orbiting our Sun. And above 1000°F it is significantly hotter. WASP-96 b orbits extremely close to its Sun-like star, just one-ninth the distance between Mercury and the Sun, completing one revolution every 3½ Earth days.
The combination of its large size, short orbital period, puffy atmosphere, and lack of contaminating light from nearby sky objects makes WASP-96 b an ideal target for atmospheric observations.
On June 21, Webb’s Near-Infrared Imager and Slitless Spectrograph (NIRISS) measured light from the WASP-96 system for 6.4 hours as the planet moved across the star. The result is a light curve showing the overall dimming of the starlight during the pass and a transmission spectrum revealing the change in brightness of individual wavelengths of infrared light between 0.6 and 2.8 microns.
While the light curve confirms the planet’s properties already determined by other observations—the planet’s existence, size, and orbit—the transmission spectrum reveals previously hidden details of the atmosphere: an unmistakable signature of water, indications of haze, and evidence of clouds. which were thought not to exist based on previous observations.
The transmission spectrum is made by comparing starlight filtered through the planet’s atmosphere as it moves through the star with the unfiltered starlight detected when the planet is next to the star. Researchers are able to detect and measure the abundance of key gases in the planet’s atmosphere based on the absorption pattern—the locations and heights of the peaks on the graph. In the same way that people have distinctive fingerprints and DNA sequences, atoms and molecules have characteristic patterns of wavelengths that they absorb.
The spectrum of WASP-96 b captured by NIRISS is not only the most detailed near-infrared transmission spectrum of an exoplanet atmosphere yet captured, but also covers a remarkably wide range of wavelengths, including visible red light and part of spectrum not previously accessible by other telescopes (wavelengths longer than 1.6 microns). This part of the spectrum is particularly sensitive to water, as well as other key molecules such as oxygen, methane and carbon dioxide, which are not immediately apparent in the WASP-96 b spectrum, but which should be detectable in other exoplanets planned for observation by Webb.
Researchers will be able to use the spectrum to measure the amount of water vapor in the atmosphere, constrain the abundance of various elements such as carbon and oxygen, and estimate the temperature of the atmosphere with depth. They can then use this information to infer the planet’s overall composition, as well as how, when and where it formed. The blue line in the graph is the best-fit model that takes into account the data, the known properties of WASP-96 b and its star (eg, size, mass, temperature), and the inferred characteristics of the atmosphere.
The exceptional detail and clarity of these measurements is made possible by Webb’s state-of-the-art design. Its 270-square-foot gold-plated mirror efficiently collects infrared light. Its precision spectrographs spread the light into rainbows of thousands of infrared colors. And its sensitive infrared detectors measure extremely subtle differences in brightness. NIRISS is able to detect color differences of only about one thousandth of a micron (the difference between green and yellow is about 50 thousandths of a micron) and differences in brightness between these colors of a few hundred parts per million.
In addition, Webb’s exceptional stability and its orbital location around Lagrange Point 2, roughly a million miles from the polluting effects of Earth’s atmosphere, provide a continuous view and clean data that can be analyzed relatively quickly.
The extremely detailed spectrum – made by simultaneously analyzing 280 individual spectra taken during the observation – gives just a hint of what Webb has in store for exoplanet research. Over the next year, researchers will use spectroscopy to analyze the surfaces and atmospheres of several dozen exoplanets, from small rocky planets to gas- and ice-rich giants. Almost a quarter of Webb’s Cycle 1 observing time is devoted to studying exoplanets and the materials that form them.
This NIRISS observation shows that Webb has the power to characterize the atmospheres of exoplanets – including those of potentially habitable planets – in exquisite detail.
The James Webb Space Telescope is the world’s leading space science observatory. Webb will solve mysteries in our solar system, look beyond distant worlds around other stars, and explore the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.
NASA Headquarters manages the mission for the agency’s Science Mission Directorate. NASA’s Goddard Space Flight Center in Greenbelt, Maryland, operates Webb for the agency and oversees mission work by the Space Telescope Science Institute, Northrop Grumman and other mission partners. In addition to Goddard, several NASA centers contributed to the project, including the Johnson Space Center in Houston, the Jet Propulsion Laboratory in Southern California, the Marshall Space Flight Center in Huntsville, Alabama, the Ames Research Center in California’s Silicon Valley, and others.
NIRISS is provided by the Canadian Space Agency. The instrument was designed and built by Honeywell in collaboration with the University of Montreal and the National Research Council of Canada.
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