The field of exoplanet studies continues to grow by leaps and bounds, with over 5,900 confirmed discoveries to date. Thanks to improved methods, instruments, and next-generation telescopes, the field is transitioning from exoplanet discovery to characterization. This is one of the main science objectives of the James Webb Space Telescope (JWST), and it has not disappointed! Thanks to Webb's advanced optics and sophisticated instruments, scientists can directly image exoplanets and gain new insights into how they form and what their atmospheres are composed of.
In particular, Webb has enabled the study of young planetary systems that are still in the process of formation in infrared wavelengths. In a recent study, a team of astrophysicists reported the detection of two giant planets around a Sun-like star (YSES-1) over 310 light-years from Earth. Using Webb's Near-Infrared Spectrometer (NIRSpec), the team was able to image these two young planets in extraordinary detail and detected the presence of silicate clouds in their atmospheres. Studying these planets provides new insights into the early-phase evolution of planetary systems.
The study was led by Dr. Kielan K. W. Hoch, an astrophysicist and Giacconi Fellow, and multiple colleagues from the Space Telescope Science Institute (STScI). They were joined by researchers from the Instituto de Estudios Astrofísicos, the Millennium Nucleus on Young Exoplanets and their Moons (YEMI), the Max Planck Institute for Astronomy (MPIA), the Lunar & Planetary Lab, the Leiden Observatory, the California Institute of Technology (Caltech), the Observatoire de la Cote d'Azur, the Observatoire de Paris, the European Southern Observatory (ESO), the European Space Agency (ESA), the NASA-Goddard Space Flight Center, and multiple universities.
Artist's impression of the JWST in space. Credit: NASA/JPL-Caltech
Studying young systems is vital to understanding how the Solar System came to be. By observing planets form in real-time, scientists can determine what chemical ingredients were present and how long the process took. Previous studies have revealed much about young planets, including indirect evidence of clouds, photochemistry, and diverse chemical elements. While Brown Dwarfs have also been observed directly, it was impossible to image young exoplanets before Webb. Given that YSES-1 is still young (about 27 million years old), any planets orbiting the star will still be warm, making them detectable in infrared wavelengths.
Using Webb's NIRSpec instrument, the researchers obtained broad spectra from the atmospheres of two giant exoplanets around the young star, designated YSES-1 b and c. The team's results showcase the capabilities of Webb, which provided the most detailed dataset of a multi-planet system to date. As co-author Dr. Evert Nasedkin, a Postdoctoral Fellow in Trinity College Dublin's (TCD) School of Physics, said in a TCD press release:
When we looked at the smaller, farther-out companion, known as YSES 1-c, we found the tell-tale signature of silicate clouds in the mid-infrared. Essentially made of sand-like particles, this is the strongest silicate absorption feature observed in an exoplanet yet. We believe this is linked to the relative youth of the planets: younger planets are slightly larger in radius, and this extended atmosphere may allow the cloud to absorb more of the light emitted by the planet.
Using detailed modelling, we were able to identify the chemical composition of these clouds, as well as details about the shapes and sizes of the cloud particles. Overall, this work highlights the incredible abilities of JWST to characterise exoplanet atmospheres. With only a handful of exoplanets that can be directly imaged, the YSES-1 system offers unique insights into the atmospheric physics and formation processes of these distant giants.
This image, captured by the SPHERE instrument on ESO's Very Large Telescope, shows the star TYC 8998-760-1 accompanied by two giant exoplanets. Credit: ESO/Bohn et al.
The team also noted the presence of a circumplanetary disk around YSES-1 b, one of the two giant exoplanets. This could be material accreting onto the planet, which could lead to the formation of moons, much like the icy moons orbiting Jupiter, Saturn, and the other gas giants in the Solar System. So far, only three other such disks have been identified around objects significantly younger than YSES-1 b, raising new questions about how long circumplanetary disks exist. As Dr. Hoch noted, these observations present opportunities to learn more about how the Solar System formed billions of years ago:
"The YSES-1 system planets are also too widely separated to be explained through current formation theories, so the additional discoveries of distinct silicate clouds around YSES-1 c and small hot dusty material around YSES-1 b lead to more mysteries and complexities for determining how planets form and evolve. This research was also led by a team of early career researchers such as postdocs and graduate students who make up the first five authors of the paper. This work would not have been possible without their creativity and hard work, which is what aided in making these incredible multidisciplinary discoveries."
