Some elements that make WASP-127b special, compared to the planets in our Solar System. Credit: David Ehrenreich/Universit de Genve, Romain Allart/Universit de Montral.
A team of international astronomers have not only found clouds on distant exoplanet WASP-127b but also measured their altitudes with remarkable precision. Romain Allart presented at the Europlanet Science Congress 2021. He explained how the team was able to uncover the upper structure of the planet’s atmosphere by using data from both a space-based and ground-based telescope. This opens the door to similar studies on other distant worlds.
WASP-127b is located over 525 light-years from Earth. It is a hot Saturn, a massive planet with a similar mass to Saturn and orbiting very close to the sun. To detect patterns in starlight that is altered by chemical constituents and filtered through the atmosphere of the planet, the team watched the planet pass in front its host star. The researchers were able probe different areas of the atmosphere by combining visible light measurements from the ESPRESSO spectrograph at European Southern Observatory's Very Large Telescope, Chile, and infrared observations using the ESA/NASA Hubble Space Telescope. Some surprises were found in the results.
"First, we detected sodium as we had seen before on this type of planet. However, it was at a lower altitude than expected. The second was that there were strong water vapour signals at visible wavelengths, but not at all in the infrared. This suggests that water-vapor at lower levels may be being screened by clouds which are opaque at visible wavelengths, but transparent at the infrared', Allart of the Universit de Genve and iREx.
Combining the data from both instruments allowed the researchers to reduce the cloud altitude to an atmospheric layer of pressure between 0.3 and 0.55 millibars.
Allart stated that the cloud composition is not known, but that the clouds are not made of water droplets as on Earth. "We also have questions about the surprising location of sodium on the planet. Future research will allow us to understand more about the atmospheric structure and WASP-127b which is proving to have fascinating properties.
WASP-127b experiences temperatures of up to 1100° Celsius and 600 times more radiation than the Earth. It orbits its star in just four days. This gives the planet a radius of 1.3 times greater than Jupiter and a fifth more mass. It is one of the most dense or "fluffiest exoplanets" ever discovered.
Because of their extended nature, fluffy exoplanets are easier to observe. WASP-127b is a great candidate for atmospheric characterisation research.
The observations made by the ESPRESSO instrument by the team also suggest that WASP-127b orbits in a different direction to its star than it does in the equatorial plane.
Allart stated that such alignments are unusual for a hot Saturn in an older stellar system. It could be due to an unknown companion. WASP-127b is a unique planet with many interesting characteristics that will be studied closely in the future.
The Echelle SPectrograph For Rocky Exoplanets & Stable Spectroscopic Observations is the most accurate spectrograph in the world for radial velocity measurements. This allows for exoplanet detection.
We would like to thank Dr. Jessica Spake, and her team, for providing the HST data that was used in this study.
More information: Romain Alart et., WASP-127b: A misaligned planet, with a partly cloudy atmosphericand a tenuous sodium signature as seen by ESPRESSO (2021). Romain Allart et. al. WASP-127b: A misaligned planet, with a partly cloudy atmosphericand a tenuous sodium signature as seen by ESPRESSO (2021). DOI: 10.5194/epsc2021-438
Europlanet
