On a freakish, distant exoplanet it snows sunscreen

  • On a freakish, distant exoplanet it snows sunscreen

On a freakish, distant exoplanet it snows sunscreen

Artist's impression showing the "hot Jupiter" exoplanet Kepler-13Ab's size, compared to several planets in our solar system.

Kepler-13Ab, which is more than 1,730 light-years from Earth, is so close to its parent star that it is tidally locked.

It orbits tightly to its star, meaning its day side reaches temperatures of 2,760°C (5,000°F), while its night side is perennially cold and dark.

Astronomers at Penn State 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.

On most hot Jupiters, gaseous titanium dioxide in the dayside's upper atmosphere absorbs starlight and radiates this energy as heat, warming the air up.

Observations of the planet show it to be ferociously hot - nearly 3,000 degrees Celsius on its dayside - but incredibly the planet experiences frequent flurries of "snow" made from titanium oxide, commonly used in sunscreen which would give any visitors some respite.

The researchers suggest that, on Kepler-13Ab, high winds carry the gas to the planet's dark side. On the nighttime side the planet's huge gravity pulls down titanium oxide, which precipitates as snow.

Hot Jupiters are a class of gas giant exoplanet inferred to be physically similar to the largest planet in the solar system.

"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 the US. "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".

The observations were captured using Nasa's orbiting Hubble space telescope.

The astronomers didn't go looking for titanium oxide specifically.

At higher elevations, the planet's atmosphere gets colder, which is unusual for this type of gas giant exoplanet, the researchers said. As a result, the planet is one of the hottest worlds known, with a dayside temperature of almost 5,000 degrees Fahrenheit (2,760 degrees Celsius), researchers said. These clouds then drop the sunscreen "snow" into the lower atmosphere, where it stays, thanks to Kepler-13Ab's powerful gravity.

The astronomers used Hubble's Wide-field Camera 3 to observe Kepler-13Ab's thick atmosphere in near-infrared light.

Instead, they planned to note the day-side atmospheric temperature of the planet as it travelled behind its star during an event which is called secondary eclipse.

This process, known as a "cold trap", stops water on Earth from being lost into space by turning rising water vapour into rain and snow, which falls back to the ground.

"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.