Helium discovered for the first time on an exoplanet

When analyzing the atmosphere of the gas giant WASP-107b in the infrared range, astronomers came across the signature of the noble gas.

Helium is the second most abundant element in the universe after hydrogen and one of the main components of the gas planets Jupiter and Saturn. Astronomers have long reckoned that the noble gas is also present in the atmospheres of extrasolar gas giants, ie in the atmosphere of gas planets outside the solar system. But the evidence was missing — so far: A team around Jessica Spake from the University of Exeter has discovered helium in the atmosphere of WASP-107b using the Hubble Space Telescope.

As the researchers report in the journal Nature, the helium content of this exoplanet is likely to be quite high: “The helium we detect reaches far out into space as a faint cloud,” said co-author Tom Evans.

Unlike earlier search campaigns focusing on the ultraviolet spectrum, measurements were now made in the infrared spectrum using the Hubble telescope Wide Field Camera 3 data: scientists looked for absorption signals from so-called metastable helium atoms, which absorb in near infrared light.

“The strong helium signal we measured also shows that this technique can work to study the upper atmosphere layers of other planets,” Spake said. “Previous methods that use ultraviolet light are limited to nearby exoplanets.”

The WASP-107b, discovered last year, is about 200 light-years away and has one of the lowest densities of exoplanets known. At a size about the same as Jupiter, the planet has only about twelve percent of its mass. The helium from its atmosphere stretches out into space over several ten thousand kilometers. The assumption is that WASP-107b is slowly losing its atmosphere due to its low gravity: it is estimated that the loss is between 0.1 to 4 percent of the total mass of its atmosphere per billion in a year.

Carl Frantz

Polyglot, humanitarian, Carl was born in Germany but raised in the USA. He writes mostly on tech, science and culture.