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.
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.
Transiting a bright star, the “Neptune desert” planet HD 219666b was one of the more important early discoveries from the TESS survey. With a depth of only 0.17 per cent, the transits would be a challenge for any ground-based transit survey.
Nevertheless, we think we’ve found them in WASP-South lightcurves dating back to 2010. Here they are:
The orange lines show times of transit, as found by the WASP transit-detection algorithms. The shallow dips seem to be real, since they align both in period and in phase with the dips seen in the TESS lightcurve. The output from the WASP search algorithm is not itself that convincing:
However, the period that it finds (6.03446 days) matches the TESS period to an accuracy of 0.03 per cent, and the WASP ephemeris then predicts the times of the TESS transits bang on (they occur at 420.99999 cycles on the WASP ephemeris), which together mean that the detection must be real. Here are the WASP data folded on a template of the TESS transit:
With a depth of 0.17 per cent, the transits of HD 219666b are the shallowest that WASP has detected.
The benefit of looking for such pre-detections of TESS planets is that we can then produce a transit ephemeris based on data spanning a baseline of 8 years, rather than the 20 days spanned by the TESS transits. This means we can predict future transits to an accuracy of minutes, instead of hours, which is highly useful for future observations. Hence this WASP-South detection of HD 219666b transits is well worth an AAS Research Note.
Naturally, we at WASP are chuffed at the award of the Nobel Prize in Physics to Michel Mayor and Didier Queloz for their discovery of 51 Peg b, the first extra-solar planet found orbiting a sun-like star. Congratulations to them both! The award is a welcome boost and recognition of the burgeoning field of exoplanets.
The WASP-South camera array
When, back in 2006, we built WASP-South in South Africa and started our Southern survey for transiting exoplanets, the Geneva Observatory team led by Mayor and Queloz were the obvious collaborators, given their world-leading track-record in the radial-velocity discovery of exoplanets, and their Euler telescope with its CORALIE spectrograph, situated at La Silla in Chile.
Prof Queloz, and his then-students Michaël Gillon and Amaury Triaud, started the radial-velocity observations of WASP-South transit candidates. Since many transit candidates turn out to be transit mimics, both the transit data and RV data are necessary to prove the discovery of a planet. That collaboration still continues, and has involved the Geneva Observatory team observing 1500 WASP candidates over many hundreds of clear nights with Euler/CORALIE.
The Euler 1.2-m telescope
The result has been the discovery of over 150 exoplanets transiting bright stars, and many of them are among the most valuable exoplanets for further observation and study. So far the collaboration between Prof Queloz’s team and WASP-South has led to over 100 refereed papers in leading journals, that have so far been cited over 5000 times.
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.
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.
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.