Tag Archives: WASP-103b

Water Is Destroyed, Then Reborn in Ultrahot Jupiters

NASA JPL have put out a press release about ultra-hot Jupiters including WASP-18b, WASP-103b and WASP-121b.

The work, led by Vivien Parmentier, used the Spitzer and Hubble space telescopes to study how the planets’ atmospheres change from the irradiated day side to the cooler night side.

“Due to strong irradiation on the planet’s daysides, temperatures there get so intense that water molecules are completely torn apart. […] fierce winds may blow the sundered water molecules into the planets’ nightside hemispheres. On the cooler, dark side of the planet, the atoms can recombine into molecules and condense into clouds, all before drifting back into the dayside to be splintered again.”

Simulated views of the ultrahot Jupiter WASP-121b show what the planet might look like to the human eye from five different vantage points, illuminated to different degrees by its parent star. (Credit: NASA/JPL-Caltech/Vivien Parmentier/Aix-Marseille University)

“With these studies, we are bringing some of the century-old knowledge gained from studying the astrophysics of stars, to the new field of investigating exoplanetary atmospheres,” said Parmentier.

Harvard’s CfA have also produced a press release on the work, focusing on the analysis of WASP-103b led by Laura Kreidberg.

“A crucial observational advance by Kreidberg and her team was that they observed the planet for an entire orbit, enabling them to map the climate at every longitude and derive detailed information about the temperatures on the planet’s dayside and nightside. This is only the second time that such a complete exoplanet observation has been performed with HST.”

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The thermal phase curve of WASP-103b

I was wondering about writing a post on Laura Kreidberg’s new paper on WASP-103b when I noticed that she’d already done it. So let’s just borrow that:

Strong Sodium and Potassium absorption in the atmosphere of WASP-103b

Characterising the atmospheres of extrasolar planets is a booming activity, both from ground-based observatories and using the Hubble Space Telescope. The latest study is of the highly-irradiated and hot planet WASP-103b, which was found by WASP-South transiting a star with an ultra-short orbit of only 0.93 days (Michaël Gillon et al 2014).

Monika Lendl et al have now used the Gemini/GMOS instrument to probe its atmosphere. The main finding is prominent features caused by absorption of light by sodium (Na) and potassium (K) ions:

Such features imply that WASP-103b has relatively clear skies, since cloudy or hazy atmospheres tend to produce flat, featureless spectra. The authors explain that: “This finding is in line with previous studies on cloud occurrence on exoplanets which find that clouds dominate the transmission spectra of cool, low surface gravity planets while hot, high surface gravity planets are either cloud-free, or possess clouds located below the altitudes probed by transmission spectra”.

Spin-orbit alignments for three more WASP planets

A team led by Brett Addison has been pointing the Anglo-Australian Telescope at WASP planets, trying to discern whether the planet’s orbit is aligned with the star’s spin axis.

The rotation of the star means that one limb is approaching us, and so is blue-shifted, while the other limb is receding, and so is red-shifted. The planet can occult blue-shifted light (making a spectral line redder) and then red-shifted light. This is called the Rossiter–McLaughlin (or R–M) effect, and allows us to deduce the path of a transiting planet across the face of its star.

Rossiter-McLaughlin effect

Brett Addison and colleagues report the R–M effect for three more WASP planets, WASP-66b, WASP-87b and WASP-103b. Here are their data for WASP-87b:

WASP-87 Rossiter-McLaughlin effect

All three planets appear to have orbital axes aligned with the star’s spin axis. The authors discuss the mechanisms and timescales by which orbits get “damped” by tidal effects and so become aligned with their star.