Category Archives: WASP planets

Looking forward to WASP-79b with JWST

The bloated hot-Jupiter WASP-79b has been selected as an Early Release Science target for the James Webb Space Telescope, so is being studied with current facilities such as HST and Spitzer.

Here is a simulation of what the spectrum of WASP-79b might look like when observed with JWST, taken from a new paper by Kristin Sotzen et al.

Sotzen et al have collected together data from HST, Spitzer and the Magellan telescope in order to model the atmosphere of the planet and use that to predict the results of the JWST observations. The different coloured symbols are for different instruments of JWST, namely NIRSpec, NIRCam and NIRISS. The main spectral features are caused by water and carbon dioxide molecules. With a partially cloudy atmosphere and detectable water features, Sotzen et al confirm that WASP-79b is a prime target for JWST.

No period change for WASP-19b

Since close-orbiting hot Jupiters are expected to be gradually spiralling inwards, under the influence of tidal interactions with their stars, and since, in addition, the influence of extra, unseen planets in the system could cause changes in transit times, many groups worldwide are monitoring timings of transits of WASP planets.

The latest report on timings of WASP-19b has just been announced by Petrucci et al. The result is the following diagram, showing deviations of timings from a constant ephemeris, plotted against cycle number.

The upshot is that there is no indication of any period change, which then puts limits on how efficient the tidal bulges, caused by the gravitational interaction of the planet with the star, are at dissipating energy.

It is notable, however, that there is clear scatter about the constant-period line, beyond that expected from the error bars on the timings. This means either that the error bars are under-estimating the uncertainties (as would occur if “red noise” in the lightcurves is unaccounted for), or that there is astrophysically real scatter in the timings, perhaps caused by magnetic activity (star spots) on the surface of the star being transited. We need to better understand such timing scatter if we are to be able to judge whether claims of period changes are actually real.

WASP-121b observed by TESS

As is sometimes the way when prime observations are open access, two independent papers (Daylan et al 2019; Bourrier et al 2019) have, on the same day, announced independent analyses of the TESS lightcurve of the ultra-hot Jupiter WASP-121b.

The phase curve shows the transit (time zero), a “phase curve” modulation caused by the varying visibility of the heated face of the planet (illustrated by schematics of the planet), and the eclipse (when the planet passes behind the star, at −15 hr).

Both analyses report similar findings, saying that the heated “hot spot” directly faces the star, rather than being offset in phase, which suggests that any re-circulation of heat by planetary winds is inefficient.

The planet’s atmosphere shows a temperature inversion (it is hotter at higher altitudes), which could result from absorption of heat by molecules of titanium and vanadium oxide, and H-minus ions.

Night-side temperatures of hot Jupiters

A team from McGill University have put out a press release about the nightsides of hot Jupiter exoplanets, which, given that hot Jupiters are phase-locked, always point away from their star. Dylan Keating et al collected observations with the Spitzer Space Telescope for a sample of 12 hot Jupiters, including 7 WASP exoplanets.

They find that, while the heated daysides show a range of temperatures, the nightsides always have a similar temperature:

“The uniformity of the nightside temperatures suggests that clouds on this side of the planets are likely very similar to one another in composition. Our data suggest that these clouds are likely made of minerals such as manganese sulfide or silicates, or rocks”, Keating explained.

Caption: Schematic of clouds on the night side of a hot Jupiter exoplanet. The underlying atmosphere is over 800 C, hot enough to vaporize rocks. Atmospheric motion from the deep atmosphere or from the hotter dayside bring the rock vapour to cooler regions, where it condenses into clouds, and possibly rains down into the atmosphere below. These clouds of condensed rock block outgoing thermal radiation, making the planet’s nightside appear relatively cool from space. Credit: McGill University

The work has led to press coverage by Fox News, Sci News, UPI, and other websites.

Hints of volcanic exo-moons?

A new paper by Apurva Oza et al has proposed the interesting idea that spectral features of sodium, previously attributed to the atmospheres of hot-Jupiter exoplanets, could actually be caused by volcanos on exo-moons orbiting the planets. The volcanos would produce a cloud of material surrounding the planet:

They suggest that WASP-49b might be the prime candidate for such a system. The idea has been discussed in a press release by the University of Bern. In our Solar System, Jupiter’s moon Io has continuous volcanic activity because of tidal stresses owing to the moon being close to Jupiter’s strong gravity. The authors produce an artist’s impression of how a volcanic exomoon might look:

All this is, of course, currently speculative, but the press release has led to widespread coverage of the idea, including by the International Business Times, Fox News, ZME Science, Sputnik News and other media outlets.

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.

Extra planets in WASP-18 and WASP-126?

With the TESS satellite observing most of the WASP planets as it surveys the sky, one can use the space-based data quality to look for “transit timing variations” in the WASP planet transits. Such TTVs — slight changes in the time of recurrence of a transit — can be caused by the gravitational perturbation of other planets in the system, and thus can reveal the presence of extra planets even when they themselves do not transit.

A new paper by Kyle Pearson, of the University of Arizona, reports evidence for TTVs in the TESS light-curves of WASP-18 and WASP-126.

Here is the TESS light-curve of WASP-18, showing the transits of the known planet WASP-18b:

And here are possible changes in the transit times, varying systematically with a 2.1-day period (red line):

Here now is the TESS light-curve of WASP-126, showing transits of WASP-126b:

And here are possible TTVs varying systematically with a period of 7.7 days (red line):

The evidence is not yet sufficiently water-tight to be sure of the existence of the extra planets, without adding in further data, but this study points to lots of similar work using TESS data as it continues its multi-year survey.