If exoplanet hunters have learned anything, it’s that exoplanets and the star systems that host them can be super weird. There are hot Jupiters, diamond planets, and now a planet that apparently provides its own sunscreen in the form of titanium oxide snow. This discovery was made while using the Hubble Space Telescope to make atmospheric observations of Kepler-13Ab, which orbits the star Kepler 13 1,730 light years from Earth. While the research team based at Pennsylvania State University were unable to see the snow directly, they were able to observe its effects on temperatures at high altitudes in the planetary atmosphere.
On Earth, titanium oxide is commonly used as the active ingredient in sunscreen. On Kepler-13Ab, a planet with daytime temperatures that reach 5,000 degrees Fahrenheit and is tidally locked with its host star, the titanium oxide snow creates a phenomenon known as a “cold trap.” Cold traps can cause vapors to condense into liquids or solids in vacuum applications and are commonly used in freeze drying applications on Earth. On Kepler-13Ab, however, the titanium oxide cold trap is caused by the reflection of light from its host star, which causes the upper atmosphere of this exoplanet to be cooler than it otherwise would be.
“In many ways, the atmospheric studies we’re doing now on these gaseous ‘hot Jupiter’ kinds of planets are test beds for how we’re going to do atmospheric studies of terrestrial, Earth-like planets,” said Thomas Beatty, assistant research professor of astronomy at Penn State and the lead author of the study that was published in the October 2017 issue of The Astronomical Journal. “Understanding more about the atmospheres of these planets and how they work will help us when we study smaller planets that are harder to see and have more complicated features in their atmospheres.”
This confirms a theory that titanium oxide precipitation could occur at levels that are indirectly observable on hot, massive planets with high gravity like Kepler-13Ab. On lighter planets, the titanium oxide would not fall very far before it is swept onto the day side of the planet and evaporated again.