Category Archives: WASP planets

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”.

The orbit of WASP-12b is decaying

Here’s the latest update on the changes in the orbital period of WASP-12b, from a new paper by Samuel Yee et al.

The times of transit are getting earlier, which means that the period is decreasing slightly. By also considering the times of occultation (when the planet passes behind the star), and also the radial-velocity measurements of the system, the authors deduce that the changes are not the effect of some other planet, but are a real decay in the orbit of WASP-12b. This is expected to occur as a result of tidal interactions between the planet and its host star.

One notable conclusion is that the rate of period decay in WASP-12b is much faster than that in WASP-19b, which shows no detectable period change yet, despite it being an even shorter-period hot Jupiter, which should increase tidal interactions. Yee et al suggest that the difference could arise if the host star WASP-12 is a sub-giant star, whereas WASP-19 is not.

Update: Following an article on WASP-12b’s orbital decay, supplied by Liz Fuller-Wright of Princeton University, and appearing in phys.org and Science Daily, the work has gained media attention from CNN, Science Times, Universe Today, and the UK’s Metro.

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.