It seems astronomers are always searching for something new, something special, something groundbreaking that will lead us onto the next big discovery. And while antistars are incredibly fascinating, and I hope we discover them, I’ll be over here, watching as our ability to detect certain particles in the atmospheres of exoplanets continues to grow. In a recent paper in The Astrophysical Journal Letters, an international team of astronomers reports on finding hydroxyl — that tiny molecule consisting of one hydrogen atom and one oxygen atom — in the atmosphere of super-hot Jupiter WASP-33b.

Now, when I say super-hot, I mean that because this planet orbits its star at a distance closer than that of Mercury to our own Sun, atmospheric temps reach more than 2500˚ Celsius. That’s hot enough to melt most metals, y’all.

Finding hydroxyl on a hot Jupiter isn’t just exciting for the discovery itself, but also for the upgrade in technology that allowed the team to make the discovery. A new instrument at the Subaru Telescope in Hawai’i called the InfraRed Doppler uses absorption spectroscopy — dark lines breaking up a full rainbow of light — to detect the fingerprint of various molecules. The instrument works by using the Doppler shift of the light as the planet’s velocity changes, relative to Earth, while it orbits its host star. Basically, we can use those changes in velocity to separate the planet’s characteristics from the star’s, since the star’s velocity doesn’t change, again, relative to Earth. And then we match the dark lines with the known patterns of a variety of atoms and molecules to figure out what is in the atmosphere.

Hydroxyl is an important molecule to find. Here on Earth, it’s produced by the reaction of water vapor with atomic oxygen and is considered an ‘atmospheric detergent’ because it reacts with polluting gas like methane and carbon dioxide to essentially remove them. In the case of WASP-33b, the hydroxyl is produced by the destruction of the water vapor under the high heat of the star. And confirm the likelihood of this explanation is the very weak signal of water vapor in the data.

But why bother with hot Jupiters? As co-author Dr. Neale Gibson states: The science of extrasolar planets is relatively new, and a key goal of modern astronomy is to explore these planets’ atmospheres in detail and eventually to search for ‘Earth-like’ exoplanets – planets like our own. Every new atmospheric species discovered further improves our understanding of exoplanets and the techniques required to study their atmospheres and takes us closer to this goal.

And co-author Chris Watson adds: While WASP-33b may be a giant planet, these observations are the testbed for the next-generation facilities like the Thirty Meter Telescope and the European Extremely Large Telescope in searching for biosignatures on smaller and potentially rocky worlds, which might provide hints to one of the oldest questions of humankind, ‘Are we alone?’

More Information

Astrobiology Center press release

Trinity College press release

Queen’s University Belfast press release

“First Detection of Hydroxyl Radical Emission from an Exoplanet Atmosphere: High-dispersion Characterization of WASP-33b Using Subaru/IRD,” Stevanus K. Nugroho et al., 2021 March 23, The Astrophysical Journal Letters