Using the Hubble Space Telescope, astronomers found a hot exoplanet where the atmosphere "snows" titanium dioxide, an ingredient used by sunscreens.

Hot Jupiter

The observations on this hot Jupiter mark the first detection of the process known as cold trap on an exoplanet.

Hot Jupiters are a class of gas giant exoplanet inferred to be physically similar to the largest planet in the solar system. Unlike our own Jupiter, however, where one year is equivalent to 12 Earth-years, these exoplanets have an orbital period of less than 10 days.


In the study published in The Astronomical Journal, study researcher Thomas Beatty, from Penn State, and colleagues studied the atmosphere of planet Kepler-13Ab using Hubble's Wide Field Camera 3.

Kepler-13Ab is one of the hottest known exoplanets with dayside temperature of about 5,000 degrees Fahrenheit. The exoplanet is tidally locked, which means that one of the planet's sides always faces the star, and the other side faces perennial nighttime.

Titanium Oxide In Hot Jupiters

Hubble gathered data as the extraterrestrial world traveled behind its parent star, a transit event known as secondary eclipse. Data revealed that the sunscreen snowfall occurs only on the planet's night side.

The researchers also found that the atmosphere of the exoplanet is cooler at higher altitudes, the opposite of observations made on other hot Jupiters.

In other hot Jupiters, titanium oxide in the atmosphere absorbs light and then radiates this as heat, which makes the atmosphere warmer at higher altitudes.

Based on their findings, the researchers think that the titanium oxide was removed from the daytime side of the exoplanet. Without it to absorb light on the daytime side, the atmospheric temperature there becomes colder with higher altitude.

"We find that Kepler-13Ab possesses a noninverted, monotonically decreasing vertical temperature profile," the researchers wrote in their study. "Due to the relatively high mass and surface gravity of Kepler-13Ab, we suggest that the apparent lack of an inversion is due to cold-trap processes in the planet's atmosphere."

The titanium oxide gas was possibly carried around by powerful winds, which condensed it into cloud-forming crystalline flakes. The surface gravity of the planet also appears to influence the snowing process.

"On the nighttime side the planet's immense gravity pulls down titanium oxide and precipitates as snow," the Hubblesite explained. "Hubble observations of the planet's atmospheric temperature profile represent the first time astronomers have detected this precipitation process, called a 'cold trap,' on an exoplanet."

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