Silicate clouds discovered in atmosphere of distant exoplanet

(Press-News.org) Astrophysicists have gained precious new insights into how distant “exoplanets” form and what their atmospheres can look like, after using the James Webb Telescope to image two young exoplanets in extraordinary detail. Among the headline findings were the presence of silicate clouds in one of the planet’s atmospheres, and a circumplanetary disk thought to feed material that can form moons around the other. 

In broader terms, understanding how the “YSES-1” super-solar system formed offers further insight into the origins of our own solar system, and gives us the opportunity to watch and learn as a planet similar to Jupiter forms in real time.

“Directly imaged exoplanets—planets outside our own Solar System—are the only exoplanets that we can truly take photos of,” said Dr Evert Nasedkin, a Postdoctoral Fellow in Trinity College Dublin’s School of Physics, who is a co-author of the research article just published in leading international journal, Nature.“These exoplanets are typically still young enough that they are still hot from their formation and it is this warmth, seen in the thermal infrared, that we as astronomers observe.” 

Using spectroscopic instruments on board the James Webb Space Telescope (JWST), Dr Kielan Hoch and a large international team, including astronomers at Trinity College Dublin, obtained broad spectra of two young, giant exoplanets which orbit a sun-like star, YSES-1. These planets are several times larger than Jupiter, and orbit far from their host star, highlighting the diversity of exoplanet systems even around stars like our own sun. 

The main goal of measuring the spectra of these exoplanets was to understand their atmospheres. Different molecules and cloud particles all absorb different wavelengths of light, imparting a characteristic fingerprint onto the emission spectrum from the planets. 

Dr Nasedkin said: “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.” 

The inner planet, YSES-1b offered up other surprises: while the whole planetary system is young, at 16.7 million years old, it is too old to find signs of the planet-forming disk around the host star. But around YSES-1b the team observed a disk around the planet itself, thought to feed material onto the planet and serve as the birthplace of moons – similar to those seen around Jupiter. Only three other such disks have been identified to date, both around objects significantly younger than YSES-1b, raising new questions as to how this disk could be so long-lived.

Dr Nasedkin added: “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.” 

In broad terms, understanding how this super-solar system formed offers further insight into the origins of our own solar system, giving us an opportunity to watch as a planet similar to Jupiter forms in real time. Understanding how long it takes to form planets, and the chemical makeup at the end of formation is important to learn what the building blocks of our own solar system looked like. Scientists can compare these young systems to our own, which provides hints of how our own planets have changed over time.

Dr Kielan Hoch, Giacconi Fellow at the Space Telescope Science Institute, said: “This program was proposed before the launch of JWST. It was unique, as we hypothesised that the NIRSpec instrument on the future telescope should be able to observe both planets in its field of view in a single exposure, essentially, giving us two for the price of one. Our simulations ended up being correct post-launch, providing the most detailed dataset of a multi-planet system to-date.”

“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 leads 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.”

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