Category Archives: Hot Jupiters

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.

Early arrival of WASP-4b transits

As NASA’s TESS satellite surveys the Southern sky is it observing many of the WASP planets. One interesting piece of analysis is to check how the transit timings compare with predictions, to look for changes in the orbital periods.

Here’s a plot from a new paper by Luke Bouma et al.

The orange Gaussians show the error range within which TESS-observed transits would be expected to occur, based on previous data, if there has been no change in the period. The blue Gaussians are the actual TESS measurements.

For most of the planets the two ranges overlap, which means the transit times are as expected. For WASP-4 (top-left), however, the transits arrived early by 80 secs, too much to be accounted for by the expected error in the ephemeris.

This suggests that the period of WASP-4b might be changing rather rapidly.

Since TESS is likely to re-observe the Southern hemisphere in future years, it will be interesting to see what happens next.

NASA’s multimedia presentation on WASP-12b

NASA has been producing presentations for its website: Exoplanet Exploration: Planets Beyond our Solar System. One of these features WASP-12b, chosen because its short-period orbit and large, bloated radius mean that the shape of the planet is distorted by the host-star’s gravity into an egg-shaped Roche lobe.

Meanwhile the Interesting Engineering website has produced a compilation of seven “weird” exoplanets, of which one is the possible ring-system planet found in WASP data, J1407b.

WASP-134b and WASP-134c: a pair of warm Jupiters

Most of the planets that WASP discovers are “hot Jupiters”, often defined as having an orbital period less than 10 days, though they clump at periods of 3 to 5 days. Occasionally we find “warm Jupiters”, with periods greater than 10 days. There seem to be far fewer of these (and not just because they’re harder to find, which they are, owing to being less likely to transit, because they are further away, and because they produce fewer transits because of the longer periods).

Our latest discovery paper, led by David Anderson, announces the WASP-134 system. An analysis of the radial-velocity observations looks like this:

There are clearly two different cycles from two different planets. Both are warm Jupiters. The inner one (upper panel) has a period just over 10 days while the outer one (lower panel) has a 70-day period. Both orbits are eccentric (the fits are clearly not sinusoids) and both planets have a mass of about one Jupiter.

This is relatively rare. Few systems are known where a shorter-period, Jupiter-mass planet has a Jupiter-mass companion with an orbit as short as 70 days. (Several systems are known where the companion is much further out, with a period of hundreds of days.)

The presence of two such planets makes it unlikely that the inner one got to its present position by the Lidov–Kozai “high eccentricity migration” pathways that are thought to explain many hot Jupiters. Such a pathway for one planet would be disrupted by the presence of the second planet.

This means that it is more likely that the two planets, WASP-134b and WASP-134c, either formed where they are, or moved inwards by “disc migration” mechanisms. Thus the two WASP-134 planets are perhaps a different population, with a different past history, than the majority of the planets found by WASP.