The infrared observatory is delving deep into the atmospheres of every kind of exoplanet, as Ezzy Pearson finds out
In the 1980s, as NASA was putting the finishing touches to the Hubble Space Telescope, discussions began to turn to what the agency’s next grand orbital observatory would be. The design they came up with was a huge, 6.5m-wide infrared observatory that could peer back through distance, dust and even time to view the dim light of the earliest galaxies, and which we now know as the James Webb Space Telescope (JWST).
At the time of those first discussions, humanity had yet to even find a hint that there were planets orbiting around other stars. That changed in 1992, when it was announced that the first-ever confirmed alien world had been found around PSR B1257+12, sparking three decades of exoplanet exploration.
Astronomers have now catalogued over 5,000 verified exoplanets, with as many more awaiting official confirmation.
For most of these worlds, however, we have only a few scant details – perhaps only how long they take to orbit, their size and their mass. This is enough information to roughly gauge a planet’s density and so reveal if it’s mostly made of heavy rock or less dense gas; but it doesn’t tell you what the planet is actually like. This is where JWST steps in. Though it wasn’t designed for it, the telescope can look into an exoplanet’s atmosphere and even pick out planets themselves as they orbit around their host star. What’s more, it can do it around more types of planet than ever before.
“JWST is looking across the whole range of exoplanet sizes,” says Hannah Wakeford from Bristol University. “We have things that are rocky and smaller than Earth, all the way up to gas giants twice the size of Jupiter.”
Sifting through starlight
Wakeford and her team investigate what are known as transiting exoplanets. These planets pass in front of their star (from the perspective of Earth), blocking out a tiny bit of the star’s light. Most exoplanet-hunting missions, such as NASA’s Kepler or TESS (the Transiting Exoplanet Survey Satellite), find their planets by looking for tiny dips in a star’s brightness. Once these have pinpointed the location of a likely planet, JWST can slew in for a closer look.
“With JWST we’re spec
