Now, for the first time, astronomers have found a telltale sign of carbon dioxide above a gas giant in another star system. The discovery comes thanks to the James Webb Space Telescope (JWST), which has enabled astronomers to peer into the distant skies with better resolution than any telescope before. It is an exciting result in itself. It’s also something of a dress rehearsal that JWST might see the same on smaller Earth-like planets. The carbon dioxide signal coming from Webb seemed clear. NASA, ESA, CSA, Leah Hustak (STScI), Joseph Olmsted (STScI) What’s new – The planet in the hand (or lens, as we say) is a gas giant called WASP-39b. As WASP-39b passed in front of its star from our perspective, some of that star’s light peeked into the planet’s atmosphere. In the process, the component blocked certain wavelengths of the electromagnetic spectrum of this distant starlight. Different chemicals left different “fingerprints” in the spectrum. Astronomers from Earth can play celestial forensics: They can examine these fingerprints and reconstruct which chemicals caused them. It is a type of measurement called spectroscopy. JWST has an instrument called NIRSpec designed to do just that. In the case of WASP-39b, astronomers found spectral signatures in the part of the electromagnetic spectrum with wavelengths between 4.1 and 4.6 microns [4100 to 4600 nanometers], which is deep in the infrared. These balls show a clear signature of carbon dioxide. Here is the background – WASP-39b is located about 700 light-years from Earth, in the direction of the constellation Virgo. WASP-39b is a gas giant, about a quarter of the mass of Jupiter, but still larger than the radius of Jupiter. It orbits very close to its host star: about one-twentieth the distance between Earth and our Sun. Astronomers can count their lucky stars that WASP-39b’s orbit is aligned in a way that allows us to see it end-to-end. The planet’s size and close proximity to its star, then, mean that when the planet passes in front of its sun, it blots out enough light to slightly dim the star. Our organs can observe this subtle drop. It is a common way of finding exoplanets, especially large ones. It was exactly how astronomers found WASP-39b in 2011. The name comes from the Wide Angle Search for Planets (WASP), the survey of the sky that astronomers used to find it. The way WASP-39b was discovered also means the world is a ripe target to search for its atmosphere. JWST’s flyby was not the first attempt by astronomers to observe WASP-39’s atmosphere. In 2018, scientists using NASA’s Hubble and Spitzer telescopes found traces of water vapor on the planet. WASP-39b was not imaged directly. Rather, the planet passes in front of the star, causing a noticeable dip in its light. NASA, ESA, CSA, Leah Hustak (STScI), Joseph Olmsted (STScI) Why it matters – Astronomers have observed other gases, such as methane and water vapor, in the atmospheres of exoplanets. But carbon dioxide has proven harder to find – until now. JWST can survey with far better resolution than any telescope before. Scientists did not hesitate to praise his resolution. “Seeing the data for the first time was like reading a poem in its entirety, when before we only had every third word,” said Laura Kreidberg of the Max Planck Institute for Astronomy in Germany. While there are many reasons why carbon dioxide can enter an atmosphere—from biological activity to chemical processes in rocks to an industrial civilization—there are a few things scientists can learn from its presence. By measuring the carbon dioxide in a gas giant’s atmosphere, astronomers can learn how much gaseous material (as opposed to solid material) formed on the planet. What’s next – Some of JWST’s mission objectives revolve around exoplanets. Scientists hope to use the telescope to better understand how exoplanets form, what exoplanets look like and what life they might harbor. WASP-39b is not really a target for finding life. Not only is it a gas giant, but its proximity to its star means it simmers at 900 degrees Celsius [1650 degrees Fahrenheit]. But the list of Earth-sized worlds at cooler distances continues to grow. This discovery, then, is a good sign that the telescope has the potential to make the same measurements as their atmospheres, if they exist. “The detection of such a clear carbon dioxide signal in WASP-39b bodes well for detecting atmospheres on smaller Earth-sized planets,” Natalie Batalha, an astronomer at the University of California, Santa Cruz, said in a press statement. Don’t be surprised if more exoplanet-related discoveries follow in succession in the coming months. This discovery came from what JWST officials call the Early Release Science program, intended to get JWST’s findings into the hands of exoplanet hunters as soon as possible. It’s clear that astronomers have barely scratched the surface (or atmosphere, as it were) of what JWST can see. LEARN SOMETHING NEW EVERY DAY.
