On a bizarre, distant exoplanet, it snows sunscreen

27 Oct 2017

An illustration of the planet Kepler-13Ab, which circles very close to its host star, Kepler-13A. Image: NASA, ESA and G Bacon (STScI)

The Hubble Space Telescope has spotted a ferociously hot, distant exoplanet where it actually ‘snows’ sunscreen.

Our ability to analyse the atmosphere of exoplanets light years away has increased significantly in recent years, and now it is starting to reveal some truly bizarre worlds.

In a paper published to The Astronomical Journal, a team of researchers from Pennsylvania State University has found one such oddity, designated Kepler-13Ab, at a distance of 1,730 light years from Earth.

Observations of the planet show it to be extremely hot – almost 3,000C 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.

Unfortunately, they would need to bottle up this ‘sunscreen’ as it only occurs on the planet’s permanent night-time side and not on the boiling daytime side that always faces its nearby star.

Simulations and analysis of its make-up suggest that titanium oxide is carried around the night-time side by powerful winds, where it condenses into crystalline flakes, forms clouds and precipitates as snow.

Also, because Kepler-13Ab has incredibly strong surface gravity – six times that of Jupiter – the titanium oxide snow is pulled out of the upper atmosphere and trapped in the lower atmosphere.

Kepler comparison

Image: NASA, ESA and A Feild (STScI)

Helps us search for new Earths

The researchers determined all this by analysing the planet’s atmosphere,  showing that it is cooler at higher altitudes, contrary to what they were expecting.

This finding led the researchers to conclude that a light-absorbing gaseous form of titanium oxide, commonly found in this class of star-hugging, gas giant planet known as a ‘hot Jupiter’, has been removed from the dayside’s atmosphere.

This makes it the first instance that a ‘cold trap’ has been spotted on an exoplanet by the Hubble Space Telescope.

“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,” said lead researcher Thomas Beatty.

“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.”

Colm Gorey was a senior journalist with Silicon Republic