LOS ANGELES, Oct. 27 (Xinhua) -- By using the NASA's Hubble Space Telescope, a team of astronomers have found a hot giant exoplanet with an atmosphere that snows titanium oxide, the active ingredient in sunscreen. These observations are the first detections of this "snow-out" process, called a "cold trap," on an exoplanet, researchers say.
The new discovery, published in October 2017 issue of The Astronomical Journal, provides insight into the complexity of weather and atmospheric composition on exoplanets, and may someday be useful for gauging the habitability of Earth-size planets.
"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," Thomas Beatty, the lead author of the study and assistant research professor of astronomy at Penn State, said in a statement.
"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."
The Penn State research team targeted planet Kepler-13Ab, a planet that's six times more massive than Jupiter, the largest planet in the solar system, and that lies 1,730 light-years from Earth.
Kepler-13Ab is very close to its host star, completing one orbit every 1.8 Earth days. Like many other tightly orbiting worlds, Kepler-13Ab is "tidally locked," always showing the same face to its star. So, it has a dayside and a nightside.
The dayside temperature of Kepler-13Ab is nearly 2760 degrees Celsius. As a result, the planet is one of the hottest of the known exoplanets.
The team discovered that the sunscreen snowfall happens only on the planet's permanent nighttime side. The Hubble observations revealed that this giant planet's atmosphere is cooler at higher altitudes, a surprising result, given that other "hot Jupiter" exoplanets tend to display the opposite pattern.
Intrigued by this surprising discovery, 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, according to the study.
The astronomers suggest that powerful winds on Kepler-13Ab carry the titanium oxide gas around, condensing it into crystalline flakes that form clouds. Kepler-13Ab's strong surface gravity 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.
"Understanding what sets the climates of other worlds has been one of the big puzzles of the last decade," said Jason Wright, associate professor of astronomy at Penn State, and one of the study's co-authors. "Seeing this cold-trap process in action provides us with a long sought and important piece of that puzzle."
The team's observations confirm a theory from several years ago that this kind of precipitation could occur on massive, hot planets with powerful gravity.
