Setting stunning space pictures aside, the bulk of the James Webb Space Telescope’s most profound scientific work — the where-do-we-come-from, are-we-alone stuff — will probably involve little squiggles on graphs of a planet orbiting a distant star.
Many astronomers want to sniff out which molecules swirl and waft through the atmosphere of planets around other stars. But they face at least two major hurdles. First, attempting such a measurement strains even the best contemporary technology. And second, many of the planets we have attempted to study so far seem to be blanketed in layers of clouds, which block our gaze.
Enter Webb’s glimpse of WASP-96b, a gas giant planet orbiting a sun-like star 1,120 light-years from Earth. Its mass is more than that of Saturn but only about half as much as Jupiter’s. Blissfully, for whatever reason, ground-based observations proved in 2018 that this particular planet has clear skies, a boon to astronomers hoping to peer in.
The new Webb measurements show evidence of water vapor, hazes and some previously unseen clouds, too.
“This is great to see,” said Jonathan Fortney, an astronomer at the University of California, Santa Cruz. He added that the traces of clouds where none were expected is a surprise. “I don’t know what to say!”
Seeing all this required careful timing. From our solar system’s perspective, WASP-96b sweeps across the surface of its star every three and half days, blotting out a small fraction of starlight during that transit passage. During that time, as the Webb watched, an even smaller number of light rays passed through the ring of atmosphere around the planet, providing the spectral fingerprints of floating molecules.
Over time, measurements like these should help us understand the birth of gas giant planets like WASP-96b — and our own Saturn and Jupiter, as well — during the formation of stars systems, clock climate patterns sweeping around them and, just maybe, for smaller worlds, enable searches for signs of life.