WASP-96b: A first look from the James Webb Telescope

Stunning space images aside, most of the James Webb Space Telescope’s most in-depth scientific work — the where-do-we-come-from-are-we-alone stuff — will likely involve little flourishes on graphics of a planet orbiting a distant star.

Many astronomers want to sniff out which molecules swirl and float around other stars through planetary atmospheres. But they face at least two major hurdles. First, attempting such a measurement is taxing on even the best contemporary technology. And second, many of the planets we’ve tried to study so far appear to be covered by cloud layers that block our view.

Enter Webb’s view of WASP-96b, a gas giant planet orbiting a Sun-like star 1,120 light-years from Earth. Its mass is greater than that of Saturn, but only about half that of Jupiter. Fortunately, for whatever reason, ground-based observations in 2018 proved that this particular planet has clear skies, a boon to astronomers hoping to look inside.

The new Webb measurements also show evidence of water vapour, haze and some previously invisible clouds.

“It’s great to see,” said Jonathan Fortney, an astronomer at the University of California, Santa Cruz. He added that the trails of clouds where none were expected come as a surprise. “I don’t know what to say!”

Seeing all of this required careful timing. From our Solar System’s perspective, WASP-96b sweeps across its star’s surface every three and a half days, blotting out a small portion of starlight during this transit passage. During the time that Webb watched, an even smaller number of rays of light 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 — as well as our own Saturn and Jupiter — during the formation of star systems, timing climate patterns around them, and, just perhaps, for smaller worlds enable the search for signs of life.

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