The search for water on exoplanets is one of the most exciting and important science challenges of our time. Technology advancements have made it feasible to closely examine the atmospheres of transiting exoplanets, providing details about their chemistry, temperature distributions, and the presence of clouds and winds. This article will examine a recent investigation on the hot Neptune WASP-166 b, which was seen by the European Extremely Large Telescope (ESPRESSO III).
WASP-166 b is an inflated super-Neptune exoplanet that orbits an F9-type star in a short orbit of 5.4 days. Despite its close orbit, WASP-166 b has managed to preserve its atmosphere, making it a benchmark target for exoplanet atmosphere studies in the so-called “Neptune desert”, which refers to the lack of Neptune-sized planets in close orbits around their hosts.
Two transits of WASP-166 b were examined by a team of scientists led by M. Lafarga from the Department of Physics using high-resolution spectroscopy to identify and characterize the planet’s atmosphere. The team estimated limitations on the abundance of water and the altitude of a cloud layer at the same time using a cross-correlation-to-likelihood mapping, which indicates a low abundance of water and/or high abundance of clouds.
Spectroscopic observations taken from the ground are affected by spectral features produced by the Earth’s atmosphere, known as telluric contamination. The effect of telluric is especially relevant when trying to study water in exoplanet atmospheres. The researchers noticed that a standard principal component analysis (PCA) algorithm resulted in very strong telluric residuals, so they optimized the performance of the PCA to minimize the presence of telluric in the cross-correlation and log likelihood functions.
Despite these difficulties, the researchers inadvertently discovered a water signal that was blue-shifted away from the planetary rest frame by about 5 km s-1. Due to the capabilities of ESPRESSO and the Very Large Telescope’s collecting ability, the injection and retrieval of model spectra demonstrated that a solar-composition, cloud-free atmosphere would be identified at high significance, albeit only in the visible (VLT).
This study provides further insight into the Neptune desert planet WASP-166 b and the search for water on exoplanets. The researchers hope that this work will lay the foundation for future studies, including observation with the James Webb Space Telescope (JWST).
The detection of water on exoplanets is a critical step in the search for life beyond our solar system. The study of WASP-166 b with ESPRESSO III highlights the advances in technology that are making it possible to explore the atmospheres of transiting exoplanets in greater detail.
As we continue to push the limits of our understanding, we may soon discover the answer to one of the biggest questions of all time: is there life on other planets?
Source : Lafarga, Marina et al. “The hot Neptune WASP-166 b with ESPRESSO III: A blue-shifted tentative water signal constrains the presence of clouds.” (2023). https://doi.org/10.48550/arXiv.2302.04794