Category Archives: exoplanets

NASA’s Webb identifies methane in the atmosphere of WASP-80b

Recently, NASA wrote a piece describing the discovery of the molecule methane in the atmosphere of WASP-80b, as announced by Taylor Bell et al. in Nature.

An artist’s rendering of the warm exoplanet WASP-80 b whose color may appear bluish to human eyes due to the lack of high-altitude clouds and the presence of atmospheric methane identified by NASA’s James Webb Space Telescope. Image credit: NASA.

Taylor Bell explains: “NASA has a history of sending spacecraft to the gas giants in our solar system to measure the amount of methane and other molecules in their atmospheres. Now, by having a measurement of the same gas in an exoplanet, we can start to perform an “apples-to-apples” comparison and see if the expectations from the solar system match what we see outside of it.”

The measured transit spectrum (top) and eclipse spectrum (bottom) of WASP-80 b from NIRCam’s slitless spectroscopy mode on NASA’s James Webb Space Telescope. In both spectra, there is clear evidence for absorption from water and methane whose contributions are indicated with colored contours. Image Credit: BAERI/NASA/Taylor Bell.

The NASA piece led to widespread reporting of the finding on numerous websites.

The IAU names more WASP exoplanets

The International Astronomical Union is periodically running contests to allow young people worldwide to name exoplanets, including those found by the WASP project.

Results of the 2022/23 naming process have just been announced.

The star WASP-19 is named Wattle (a genus of 1000 species of shrubs and trees native to Australia) while planet WASP-19b is Banksia (a genus of Australian wildflowers of medicinal and cultural importance to indigenous Australians).

The star WASP-43 is named Gnomon (after the astronomical instrument) while planet WASP-43b is Astrolábos (Greek for the astronomical instrument used in navigation).

The star WASP-63 is named Kosjenka while planet WASP-63b is Regoč (the names being characters in a popular Croatian fairy tale).

The star WASP-69 is named Wouri while planet WASP-69b is Makombé (being a major river in Cameroon and its tributary).

The star WASP-121 is named Dilmun (the Sumerian name of an ancient civilisation of the Bahrain archipelago) while planet WASP-121b is Tylos (the ancient Greek name for Bahrain island.).

The star WASP-166 is named Filetdor while planet WASP-166b is Catalineta (being a sea-serpent and heroine from the Mallorcan folktale “Na Filet d’Or”).

Water vapour in the atmosphere of WASP-18b

NASA have put out a press release about observations of the ultra-hot gas-giant WASP-18b by the James Webb Space Telescope.

By measuring the radiation of the planet as it is eclipsed by its host star, once every orbit, the team, led by Louis-Philippe Coulombe, mapped out the heat of the planet’s atmosphere. With WASP-18b being so hot, water vapour is likely disassociated over much of the “day side” of the planet, where it is blasted by the host-star’s radiation. But the sensitivity of JWST allowed it to detect water vapour from cooler regions on the planet’s limbs.

A hot super-Earth in the WASP-84 planetary system

When Kepler’s K2 mission started monitoring planetary systems where WASP had previously found hot Jupiters, one of the early discoveries was extra planets in the WASP-47 system, small rocky planets with transits too shallow to have been found by WASP.

Now, a similar finding for the WASP-84 system has been announced by Gracjan Maciejewski etal. WASP found a Jupiter-sized planet in an 8-day orbit, while lightcurves from NASA’s TESS satellite also show a super-Earth planet with an orbit of 1.4 days.

The mass of both planets can be gained from the radial-velocity motion of the host star:

The new planet has a rocky, Earth-like composition.

James Webb detects carbon dioxide in the spectrum of WASP-39b

The first science paper about a transiting exoplanet observed by JWST reports the detection of carbon dioxide in the spectrum of WASP-39b.

NASA’s press release on the “Early Release Science” result gives this image:

In addition they have produced this graphic of how transit spectroscopy works:

MPIA press release: An exotic water cycle and metal clouds on the hot Jupiter WASP-121 b

Here’s another catch-up on a recent press release from MPIA, reporting on Hubble Space Telescope observations of WASP-121b.

“A group of astronomers, led by Thomas Mikal-Evans from the Max Planck Institute for Astronomy, have made the first detailed measurement of atmospheric nightside conditions of a tidally locked hot Jupiter. By including measurements from the dayside hemisphere, they determined how water changes physical states when moving between the hemispheres of the exoplanet WASP-121 b. While airborne metals and minerals evaporate on the hot dayside, the cooler night side features metal clouds and rain made of liquid gems. This study, published in Nature Astronomy, is a big step in deciphering the global cycles of matter and energy in the atmospheres of exoplanets.”

“To probe the entire surface of WASP-121 b, we took spectra with Hubble during two complete planet revolutions,” co-author David Sing from the Johns Hopkins University in Baltimore, USA, explains. With this technique and supported by modelling the data, the group probed the upper atmosphere of WASP-121 b across the entire planet and, in doing so, observed the complete water cycle of an exoplanet for the first time.

“On the side of the planet facing the central star, the upper atmosphere becomes as hot as about 3000 degrees Celsius. At such temperatures, the water begins to glow, and many of the molecules even break down into their atomic components. The Hubble data also reveal that the temperature drops by approximately 1500 degrees Celsius on the nightside hemisphere. This extreme temperature difference between the two hemispheres gives rise to strong winds that sweep around the entire planet from west to east, dragging the disrupted water molecules along. Eventually, they reach the nightside. The lower temperatures allow the hydrogen and oxygen atoms to recombine, forming water vapour again before being blown back around to the dayside and the cycle repeats. Temperatures never drop low enough for water clouds to form throughout the cycle, let alone rain.”

“Instead of water, clouds on WASP-121 b mainly consist of metals such as iron, magnesium, chromium and vanadium. Previous observations have revealed the spectral signals of these metals as gases on the hot dayside. The new Hubble data indicate that temperatures drop low enough for the metals to condense into clouds on the nightside. The same eastward flowing winds that carry the water vapour across the nightside would also blow these metal clouds back around to the dayside, where they again evaporate.

“Strangely, aluminium and titanium were not among the gases detected in the atmosphere of WASP-121 b. A likely explanation for this is that these metals have condensed and rained down into deeper layers of the atmosphere, not accessible to observations. This rain would be unlike any known in the Solar System. For instance, aluminium condenses with oxygen to form the compound corundum. With impurities of chromium, iron, titanium or vanadium, we know it as ruby or sapphire. Liquid gems could therefore be raining on the nightside hemisphere of WASP-121 b.”

The press release has been taken up by numerous media and press websites.

CHEOPS observes WASP-189b

ESA’s CHEOPS satellite was launched to produce high-quality light-curves of exoplanet systems. A new paper led by Adrien Deline of the University of Geneva now reports CHEOPS observations around the orbit of the ultra-hot-Jupiter WASP-189b. The figure shows the transit (planet passing in front of the star), the eclipse (the planet passing behind the star) and a slower variation caused by the varying visibility of the heated face of the planet.

One notable feature of the transit of WASP-189b is that it is distinctly asymmetrical. This is caused by gravity darkening, which occurs when a star is rapidly rotating. The centrifugal forces cause the equatorial regions to be pushed outwards, producing an equatorial bulge. Since the bulge is then further from the star’s centre, the surface gravity will be lower, and that means that the surface will be cooler and thus dimmer.

The illustrations below show the asymmetry, where the dashed line in the lowest panel shows the difference between a transit model both with and without gravity darkening. The right-hand panel illustrates the polar orbit of the planet.

Hot Jupiters often have polar orbits

Once a planet is found to transit its star, astronomers often try to figure out whether the planet’s orbit is aligned with the spin of the star. This is called the “obliquity”, denoted by Ψ, the angle between the orbital and stellar-spin axes.

This angle Ψ can be measured if we have enough information , including the broadening of the stellar lines caused by the star’s rotation, the perturbation of the stellar line profiles as the planet transits the star (called the Rossiter–McLaughlin effect), and the star’s rotation period.

It has long been known that many hot-Jupiter exoplanets are in aligned orbits (where the star’s spin axis is perpendicular to the orbital plane), but that a significant fraction are misaligned. Now a new paper led by Simon Albrecht reports that the misaligned planets tend to be in polar orbits, where the planet passes directly over the star’s poles.

The plot shows values for all the hot Jupiters where Ψ can be measured — of which roughly half are WASP planets — and reveals that obliquity values (y-axis) imply that the planets tend to be either aligned (low values of Ψ) or in polar orbits (Ψ near 90 degrees).

In the illustration below the planets orbit in the equatorial plane (we look along the z axis), and the arrows point along the stellar spin axes. The arrows collected around the y axis are thus the aligned systems. The rest are not evenly distributed, but are preferentially close to the orbital plane.

Although the authors discuss several mechanisms that can be causing misaligned orbits, the reason for the preponderance of planets in polar orbits is not yet understood.

Aerosol particles make WASP-69b’s atmosphere hazy

“Aerosols have a critical role in establishing energy budgets, thermal structure, and dynamics in planetary atmospheres”, declares a new paper by Raissa Estrela et al.

Aerosols make the planet’s atmosphere hazy, an effect which is more pronounced at the blue end of the spectrum. Here is the spectrum of hot-Jupiter exoplanet WASP-69b, combining Hubble Space Telescope data from several observations.

The steeply rising spectrum (the y-axis shows effective planet size, with a larger size indicating more atmospheric absorption) is modelled (blue line) by including haze from aerosol scattering. The aerosols are found to extend from millibar pressures to microbar pressures.

The authors don’t yet know the composition of the aerosols, but suggest possibilities including hydrocarbons or magnesium silicate condensates. Overall they conclude that: “These results are consistent with theoretical expectations based on microphysics of the aerosol particles that have suggested haze can exist at microbar pressures in exoplanet atmospheres”.

CHEOPS observations of WASP transits

CHEOPS, the CHaracterising ExOPlanet Satellite is ESA’s Small-class mission dedicated to recording transits of exoplanets. A new paper led by Luca Borsato presents some early observations of transits of WASP, KELT and HATnet planets.

Here, for example, are the lightcurves of two transits of WASP-8b, both plotted against phase.

The paper focuses on the transit timing, which can be as good as timing a transit to an accuracy of 13 to 16 seconds, depending on the brightness of the host star and the amount of transit covered by the observations.

One aim of such work is to look for variations in the timing of transits, caused by the gravitational perturbations of additional unseen planets in the system.