NASA’S Hubble Space Telescope found titanium dioxide, the active ingredient in most sunscreen lotions, in the form of snow precipitating in the atmosphere of a blistering hot planet outside our solar system (exoplanet), 1,730 light-years from Earth.
It’s the first time astronomers have witnessed snow on an exoplanet. Also, this sunscreen (titanium dioxide) snowfall only happens on the planet’s dark, nighttime side—a little useless! But this is where it can actually condense into crystalline flakes and form clouds to precipitate.
Initially, Hubble astronomers were not looking for titanium oxide. This exoplanet, Kepler 13-Ab was selected for study because it is one of the hottest of the known gas-giant planets known as a “hot Jupiter,” with a day-side temperature of nearly 5,000 degrees Fahrenheit (about 2,760 degrees Celcius).
They observed that Kepler 13-Ab’s atmosphere is cooler at higher altitudes, which was contrary to expectations. Past assessments of other hot Jupiters show that the upper atmospheres increase in temperature, because titanium oxide absorbs light and typically reradiates it as heat.
As such, researchers concluded that the gas form of titanium oxide, commonly found in hot Jupiters, was removed from the dayside’s atmosphere. They suggest that powerful winds carry the titanium oxide gas to the colder nighttime side, and the strong surface gravity—six times that of Jupiter’s in the case of Kepler 13Ab—induces the titanium oxide to precipitate as snow.
This process is referred to as a “cold trap,” and it is the first time astronomers have found this on an exoplanet.
Without the titanium oxide gas on the daytime side to absorb incoming light, the temperature is colder as altitude increases.
“Presumably, this precipitation process is happening on most of the observed hot Jupiters, but those gas giants all have lower surface gravities than Kepler-13Ab,” said lead researcher Thomas Beatty of Pennsylvania State University in University Park.
“The titanium oxide snow doesn’t fall far enough in those atmospheres, and then it gets swept back to the hotter dayside, revaporizes, and returns to a gaseous state.”
“In many ways, the atmospheric studies we’re doing on hot Jupiters now are testbeds for how we’re going to do atmospheric studies on terrestrial, Earth-like planets,” he added.
“Hot Jupiters provide us with the best views of what climates on other worlds are like. Understanding the atmospheres on these planets and how they work, which is not understood in detail, will help us when we study these smaller planets that are harder to see and have more complicated features in their atmospheres.”
Hubble’s Wide Field Camera 3 was used to make spectroscopic observations of Kepler-13Ab’s thick atmosphere in near-infrared light.