Monthly Archives: September 2020

Which exoplanets do we have atmospheric spectra for?

Here’s an interesting plot created by Zafar Rustamkulov (@exoZafar), a PhD student at Johns Hopkins University. He has added up all the exoplanets for which we have either transmission spectra (blue), emission spectra (red) or both (pink), and plotted the planet’s size and orbital period.

Most atmospheric characterisation has been done on the hot Jupiters (top left of the plot), since these are the easiest to study. Their large size and often bloated, fluffy outer layers produce the largest spectral signals. Smaller planets are harder to study, unless their host stars are very bright or very small (such that the fraction blocked by the planet during transit is relatively large).

For the planets for which we have over 50 spectra Zafar has added the planet’s name (though the lettering is rather small!). This shows that roughly half of the most-studied exoplanets come from the WASP survey. WASP-12b, WASP-33b and WASP-39b are in the Northern Hemisphere and came from the SuperWASP-North survey. WASP-17b, WASP-19b, WASP-31b, WASP-43b, WASP-80b, WASP-107b, WASP-121b and WASP-127b are in the South and so are from the WASP-South survey.

First results from ESA’s Cheops: WASP-189b

ESA’s Cheops satellite (the Characterising Exoplanet Satellite) started observing this year, and ESA has just put out a press release announcing its first science results. Cheops looked at transits and occultations of WASP-189b, an ultra-hot Jupiter in a polar orbit transiting a bright star.

“Only a handful of planets are known to exist around stars this hot, and this system is by far the brightest,” says Monika Lendl of the University of Geneva, Switzerland, lead author of the new study. “WASP-189b is also the brightest hot Jupiter that we can observe as it passes in front of or behind its star, making the whole system really intriguing.”

At a visual magnitude of V = 6.6, WASP-189 is the brightest host star of all the WASP planets. The discovery of the transiting hot Jupiter was announced in 2018 in a paper led by David Anderson. The exceptional nature of WASP-189 thus made it a prime target for Cheops.

The Cheops study shows that: “the star itself is interesting – it’s not perfectly round, but larger and cooler at its equator than at the poles, making the poles of the star appear brighter,” says Dr Lendl. “It’s spinning around so fast that it’s being pulled outwards at its equator!”

“This first result from Cheops is hugely exciting: it is early definitive evidence that the mission is living up to its promise in terms of precision and performance,” says Kate Isaak, Cheops project scientist at ESA.

Press coverage has included articles in CNN, CTV, the International Business Times, The Sun, The Mirror, The Daily Mail, The Express and over 30 other news sites.