Category Archives: Hubble Space Telescope

The atmosphere of the inflated hot Jupiter WASP-6b

Atmospheric characterisation of hot Jupiters continues apace, using both ground-based telescopes such as ESO’s Very Large Telescope and satellites such as Hubble.

Aarynn Carter et al have just produced a new analysis of WASP-6b:

The spectrum shows absorption due to sodium (Na), potassium (K) and water vapour, while the modelling implies that the atmosphere is partially hazy. Carter et al state that: “despite this presence of haze, WASP-6b remains a favourable object for future atmospheric characterisation with upcoming missions such as the James Webb Space Telescope.

The spectrum of the bloated, sub-Saturn-mass planet WASP-127b

Here is the latest analysis of the spectrum of WASP-127b, led by Jessica Spake and newly announced on arXiv.

The different datasets come from the Hubble Space Telescope and the Spitzer Space Telescope. Spake et al see obvious features from sodium, potassium, water and carbon dioxide. They conclude that the planet has a super-solar metallicity and that its skies are relatively cloud-free.

WASP-127b is a highly observable target since, despite being less than Saturn’s mass, it is bloated to larger than Jupiter. The puffy atmosphere projected against the host star gives results in a strong signal observable during transit. Spake et al look forward to observing the planet with the James Webb Space Telescope, and say: “the hint of a large absorption feature around 4.5 microns is strong evidence that future observations of WASP-127b with JWST will be able to measure the abundances of carbon-bearing species in its atmosphere”.

Metals streaming from the atmosphere of WASP-121b

The Hubble Space Telescope Science Institute have put out a press release about Hubble observations of WASP-121b, as reported in a new paper led by David Sing of Johns Hopkins University.

WASP-121b is one of the hottest WASP planets, since it is fiercely irradiated by being in a very tight orbit of only 1.27 days around a hot F star. The Hubble spectra show clear absorption features caused by metals including Magnesium and Iron:

“Heavy metals have been seen in other hot Jupiters before, but only in the lower atmosphere,” explains David Sing, “So you don’t know if they are escaping or not. With WASP-121b, we see magnesium and iron gas so far away from the planet that they’re not gravitationally bound.”

“The heavy metals are escaping partly because the planet is so big and puffy that its gravity is relatively weak. This is a planet being actively stripped of its atmosphere.”

The Hubble press release continues: “This exoplanet is also a perfect target for NASA’s upcoming James Webb Space Telescope to search in infrared light for water and carbon dioxide, which can be detected at longer, redder wavelengths. The combination of Hubble and Webb observations would give astronomers a more complete inventory of the chemical elements that make up the planet’s atmosphere.”

STSci have produced an artist’s impression of WASP-121b, showing how the planet’s shape is tidally distorted by the gravity of the star that it orbits:

Artwork: NASA, ESA, and J. Olmsted (STScI)

The press release has led to coverage on over 50 news and science websites, including Newsweek, CNN, Fox News, Metro, The Daily Mail, The Express, and countries including Switzerland, Germany, India, and Malaysia.

Spectral contamination from starspots on WASP-4

Here’s a topic we’ll be hearing much more about: how the observed spectrum of a transiting exoplanet is affected by transiting across star-spots. In “transmission spectroscopy” the starlight shines through the planet’s atmosphere during transit, and the easiest thing to do is assume that the star itself is a uniform light source.

But as discussed by papers led by Ben Rackham, if the planet passes over a dark region (star spot) or bright region (faculae), this would change the observed spectrum.

A new paper led by Alex Bixel about WASP-4b is the first to attempt to correct for this effect. The authors’ transit observations show a clear crossing of a starspot (the feature is shown in blue, the spot shows as a upward bump since the planet is then removing less light):

And here is the difference it makes. The blue curve is the observed spectrum, presumed to be of the planet’s atmosphere. The orange curve is then the spectrum corrected for the presence of the star spot.

The details of how to do this are complex, and are discussed at length in the above papers. The central message is that “active FGK host stars can produce such features and care is warranted in interpreting transmission spectra from these systems”.

However, there is good news in that: “stellar contamination in transmission spectra of FGK-hosted exoplanets is generally less problematic than for exoplanets orbiting M dwarfs”, and that such signals “are generally minor at wavelengths of planetary atomic and molecular features”. Overall the authors say that their study “bodes well for high-precision observations of these targets”.

Sulfanyl in the atmosphere of WASP-121b?

The latest Hubble Space Telescope spectrum of a WASP exoplanet has just been published by Thomas Evans et al. The spectrum of WASP-121b extends from near-UV wavelengths through the optical to the infra-red, combining data from three different gratings (shown in different colours in the figure):

Of particular interest is the rapid rise in the data in the near-UV (the extreme left of the plot), which is clearly out of line with the fitted model (purple lines). The rise is too rapid to be attributed to Rayleigh scattering in a clear atmosphere.

Instead, the authors suggest that it is due to sulfanyl, a molecule consisting of one sulfur and one hydrogen. Evans et al conclude that the near-UV absorber “likely captures a significant amount of incident stellar radiation at low pressures, thus playing a significant role in the overall energy budget, thermal structure, and circulation of the atmosphere”.

The work points to the ongoing importance of the Hubble Space Telescope, even after the James Webb Space Telescope is launched, since the JWST is designed for infrared astronomy, and can’t see the near-UV wavelengths that can be observed with Hubble.

Update: One of the authors, Jo Barstow, has tweeted the following thread on the @astrotweeps account:

Hubble detects helium in the atmosphere of an exoplanet for the first time

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.

Artist’s impression of the exoplanet WASP-107b showing the atmosphere boiling off under the fierce irradiation of its star. Image credit: EngineHouseVFX

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.

Note: Dozens of websites have covered the story, including Newsweek, The Independent, the International Business Times, and others.