The search for planets beyond our Solar System has grown immensely during the past few decades. To date, 4,521 extrasolar planets have been confirmed in 3,353 systems, with an additional 7,761 candidates awaiting confirmation. With so many distant worlds available for study (and improved instruments and methods), the process of exoplanet studies has been slowly transitioning away from discovery towards characterization.

For example, a team of international scientists recently showed how combining data from multiple observatories allowed them to reveal the structure and composition of an exoplanet’s upper atmosphere. The exoplanet in question is WASP-127b, a “hot Saturn” that orbits a Sun-like star located about 525 light-years away. These findings preview how astronomers will characterize exoplanet atmospheres and determine if they are conducive to life as we know it.

The research paper that describes their findings appeared in the December 2020 issue of Astronomy and Astrophysics. It was also the subject of a presentation made during the recent Europlanet Science Congress (EPSC) 2021, a virtual conference from September 13th to 24th, 2021. During the presentation, lead author Dr. Romain Allart showed how combining data from space-based, and ground-based telescopes detected clouds in WASP-127b’s upper atmosphere and measured their altitudes with unprecedented precision.

Some of the elements making WASP-127b unique, compared with the planets of our Solar System. Credits: David Ehrenreich/Université de Genève, Romain Allart/Université de Montréal.

Like many exoplanets discovered to date, WASP-127b is a gas giant that orbits very close to its parent star and has a very short orbital period – taking less than four days to complete a single orbit. The planet is also 10 billion years old, which is over twice as long as Earth (or “our” Saturn) has been around. Because of its close orbit, WASP-127b receives 600 times more irradiation than Earth and experiences atmospheric temperatures of up to 1,100C (2012F).

As a result, the planet’s atmosphere has expanded (or puffed up) to the point that it is 1.3 times as large as Jupiter but far less dense. In fact, WASP-127b is one of the least dense (or “fluffiest”) exoplanets discovered to date. This makes WASP-127b an ideal candidate for researchers working on atmospheric characterization, as the extended nature of fluffy exoplanets makes them easier to observe.

Using data obtained by the ESA/NASA Hubble Space Telescope (HST) and visible light measurements from the Very Large Telescope (VLT) at the ESO’s Paranal Observatory in Chile, the team observed WASP-127b as it made two passes in front of its star. Consistent with the Transit Method (aka. Transit Photometry), the team monitored WASP-127 for periodic dips in luminosity that indicated an exoplanet passing in front of the star (transiting) relative to the observation team.

Whereas Hubble obtained optical data that confirmed the transits, the VLT’s Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observation (ESPRESSO) instrument obtained spectra from the light passing through WASP-127b’s upper atmosphere. Dr. Allart, a Trottier Postdoctoral Researcher at the Institute for Research on Exoplanets (iREX) at the Université de Montréal, led the study.

The Very Large Telescope in Chile firing a laser from its adaptive optics system. Credit:
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