WASHINGTON: Astronomers have used the Hubble Space Telescope to find a blistering-hot giant planet outside our solar system where the atmosphere "snows" titanium dioxide - the active ingredient in sunscreen.
These Hubble observations are the first detections of this "snow-out" process, called a "cold trap," on an exoplanet, researchers said.
The finding by researchers at Pennsylvania State University in the US provides insight into the complexity of weather and atmospheric composition on exoplanets, and may be useful for gauging the habitability of Earth-size planets.
The astronomers suggest that powerful winds on Kepler- 13Ab carry the titanium oxide gas around, condensing it into crystalline flakes that form clouds.
The planet's strong surface gravity - six times greater than Jupiter's - then pulls the titanium oxide snow out of the upper atmosphere and traps it in the lower atmosphere on the nighttime side of the planet.
The team targeted planet Kepler-13Ab because it is one of the hottest of the known exoplanets. Its dayside temperature is nearly 5,000 degrees Fahrenheit.
Kepler-13Ab is so close to its parent star that it is tidally locked, so one side always faces the star while the other side is in permanent darkness.
The team discovered that the sunscreen snowfall happens only on the planet's permanent nighttime side.
The study, published in The Astronomical Journal, revealed that the giant planet's atmosphere is cooler at higher altitudes - which was surprising because it is the opposite of what happens on other hot Jupiters.
Titanium oxide in the atmospheres of other hot Jupiters absorbs light and reradiates it as heat, making the atmosphere grow warmer at higher altitudes.
Even at their much colder temperatures, most of our solar system's gas giants also have warmer temperatures at higher altitudes, researchers said.
Intrigued by this surprising discovery, the researchers concluded that the light-absorbing gaseous form of titanium oxide has been removed from the dayside of planet Kepler- 13Ab's atmosphere.
Without the titanium oxide gas to absorb incoming starlight on the daytime side, the atmospheric temperature there grows colder with increasing altitude.