Press Release (in coordination with Nature and Hubble/ESA): Astronomers using the NASA/ESA Hubble Space Telescope have detected helium in the atmosphere of the exoplanet WASP-107b. This is the first time that this element has been detected in the atmosphere of a planet outside the Solar System. The discovery demonstrates a new method for studying exoplanet atmospheres.
An international team, led by Jessica Spake of the University of Exeter, has discovered helium in the atmosphere of the exoplanet WASP-107b. The discovery was made with the Wide Field Camera 3 on the Hubble Space Telescope.
“Helium is the second-most common element in the Universe after hydrogen”, explains Jessica Spake. “It is also one of the main constituents of the planets Jupiter and Saturn in our Solar System. However, until now helium has never been detected in an exoplanet.”
WASP-107b (the 107th exoplanet discovered by the UK-led Wide Angle Search for Planets, “WASP”) was discovered in 2017 by a team led by Professor Coel Hellier of Keele University.
The team found that WASP-107b is a very low-density planet, being so puffed up and bloated that the atmosphere might be boiling off the planet under the irradiation of its host star.
“As soon as we found WASP-107b we realised it was ideal for studying the atmosphere of an exoplanet” remarks Keele astronomer David Anderson, who wrote the paper announcing WASP-107b.
Jessica Spake decided to point Hubble at WASP-107b, and, by detecting the spectral signature of irradiated helium atoms, proved that the atmosphere is indeed boiling off into space. While it had long been thought that helium would be abundant in exoplanet atmospheres, searches for it had previously been unsuccessful.
David Sing, who leads the Exeter team, says that: “Our new method, along with future telescopes, such as the James Webb Space Telescope, will allow us to analyse atmospheres of exoplanets in far greater detail than ever before.”
Jessica Spake continues. “We know that there is helium in the Earth’s upper atmosphere and this new technique may help us to detect atmospheres around Earth-sized exoplanets.”
The study was published in the paper “Helium in the eroding atmosphere of an exoplanet”, published in Nature.
NASA, ESA and JPL have put out press releases on the atmospheric spectrum of WASP-39b. The paper by Hannah Wakeford et al combined Hubble and Spitzer data to produce a comprehensive spectrum with broad spectral coverage.
“Using Hubble and Spitzer, the team has captured the most complete spectrum of an exoplanet’s atmosphere possible with present-day technology. “This spectrum is thus far the most beautiful example we have of what a clear exoplanet atmosphere looks like,” said Wakeford.”
“WASP-39b shows exoplanets can have much different compositions than those of our solar system,” said co-author David Sing of the University of Exeter. “Hopefully, this diversity we see in exoplanets will give us clues in figuring out all the different ways a planet can form and evolve.”
The strongest features in the spectrum are caused by water:
“Although the researchers predicted they’d see water, they were surprised by how much water they found in this “hot Saturn.” Because WASP-39b has so much more water than our famously ringed neighbor, it must have formed differently. The amount of water suggests that the planet actually developed far away from the star, where it was bombarded by a lot of icy material. WASP-39b likely had an interesting evolutionary history as it migrated in, taking an epic journey across its planetary system and perhaps obliterating planetary objects in its path.”
The main finding is that WASP-18b, a highly irradiated hot Jupiter in a tight orbit around a hot F-type star, is “wrapped in a smothering stratosphere loaded with carbon monoxide and devoid of water”.
“The team determined this by detecting two types of carbon monoxide signatures, an absorption signature at a wavelength of about 1.6 micrometers and an emission signature at about 4.5 micrometers.”
The findings have been reported in many media outlets including: Newsweek, The Independent, The Sun, the Daily Mail, the International Business Times, phys.org, and more than 20 other websites including Forbes magazine, who have produced the following infographic:
NASA has put out a press release about Hubble Space Telescope observations of WASP-12b. Taylor Bell et al find that WASP-12b “traps at least 94 percent of the visible starlight falling into its atmosphere”, making it “as black as fresh asphalt”.
The article explains that WASP-12b, in a very close, 1.2-day orbit, is so irradiated by its host star that “clouds probably cannot form to reflect light back into space. Instead, incoming light penetrates deep into the planet’s atmosphere where it is absorbed by hydrogen atoms and converted to heat energy”. NASA’s press release has led to coverage on several dozen websites.
WASP-12b is one of the more important of the WASP discoveries, with over 30 refereed papers so far focused on understanding it. Most notably, the fierce stellar irradiation means that material is boiling off the planet and forming a cloud surrounding it.
The article compares WASP-67b and HAT-P-38b, noting how similar they are in size and temperature, both orbiting similar stars at a similar orbital distance. But then Hubble’s Wide Field Camera 3 found that WASP-67b has a very cloudy atmosphere whereas HAT-P-38b has much clearer skies.
From the press release: Perhaps one planet formed differently than the other, under a different set of circumstances. “You can say it’s nature versus nurture,” explains co-investigator Kevin Stevenson. “Right now, they appear to have the same physical properties. So, if their measured composition is defined by their current state, then it should be the same for both planets. But that’s not the case. Instead, it looks like their formation histories could be playing an important role.”
“Astronomers measured how light from each parent star is filtered through each planet’s atmosphere. HAT-P-38 b did have a water signature indicated by the absorption-feature peak in the spectrum. This is interpreted as indicating the upper atmosphere is free of clouds or hazes. WASP-67 b, has a flat spectrum that lacks any water-absorption feature, suggesting most of the planet’s atmosphere is masked by high-altitude clouds.”
The NASA press release has been picked up and reported on several dozen science-related websites.
Credits: Artwork: NASA, ESA, and Z. Levy (STScI); Science: NASA, ESA, and G. Bruno (STScI)
Orbiting a hot F-star in only 1.27 days, WASP-121b is a highly irradiated hot Jupiter found by Laëtitia Delrez et al using the WASP-South survey. A team led by Tom Evans at Exeter has now pointed the Hubble Space Telescope at WASP-121b and found that its atmosphere shows a “stratosphere”. That is, the higher layers of the atmosphere appear to be hotter than the lower layers.
This is possible if molecules high in the atmosphere absorb radiation very efficiently. The “stratosphere” interpretation comes from finding spectral features caused by water, but seeing them in emission (as expected if the atmospheric temperature increases with height) rather than in absorption (expected if the temperature declines with height).
The data show the Hubble spectrum observed during transit using the WFC3 instrument. The red line is a model including a stratosphere. The blue lines are, for comparison, colder “brown dwarfs” which don’t have a stratosphere. The WFC3 data (circles with error bars) clearly favour the stratosphere interpretation.
NASA have put out a press release about the discovery, while the press team at Exeter have produced an illustration of the highly irradiated planet: