Scientists have scored a pristine view of a pair of exotic worlds orbiting a star more than 300 light-years away — one with sand-like clouds and another surrounded in space by moon-making material.
The discoveries come from YSES-1, a star system in the deep southern sky. Using the James Webb Space Telescope, a collaboration of NASA and its European and Canadian counterparts, a team of astronomers saw so-called "silicate clouds" directly for the first time on an exoplanet, a world far beyond our own solar system. The team's detection of a dusty disk around the sibling planet is also rare, perhaps just the third time scientists have seen one so clearly.
Webb usually observes exoplanets through indirect methods, such as transmission spectroscopy, a technique for studying a planet's atmosphere by analyzing how starlight filters through it. What distinguishes this new research is that the two worlds — YSES-1b and YSES-1c — were directly imaged, meaning the telescope captured light from the planets themselves.
Sitting far from their host star, these young planets glow from the leftover heat of their formation. Thanks to their temperature, size, and distance, the result is a clean picture of the exoplanets in thermal infrared, allowing scientists to get much more data.
"What's really cool about this system is that unlike most planets, we can actually take a picture of them!" said Evert Nasedkin in a post on the social media platform Bluesky. You can see the image further down in this story.
The idea for this groundbreaking project began long before Webb was even open for business, said Kielan Hoch, lead author of the research recently published in the journal Nature.
Scientists hypothesized the telescope could get both worlds in a single shot, "essentially giving us two for the price of one," Hoch said in a statement.
These two gas giant planets weigh five to 15 times the mass of Jupiter and orbit far from their host, a star similar to the sun. What's different is that it's only about 16.7 million years old, a mere whippersnapper compared to our middle-aged, 4.6 billion year-old sun. The planets are also in extremely distant orbits. YSES-1b, the innermost of the two, is still perhaps four times farther from its star than Pluto is from the sun.
But given only a handful of known exoplanets can be directly imaged, the study has offered scientists a unique opportunity to see an early stage of a developing star system. From these observations of the YSES-1 system — the letters in its name stand for Young Suns Exoplanet Survey — astronomers can gain insight into how planets and moons form and evolve.
Few distant worlds meet the criteria for direct imaging because planets are often millions of times fainter than the stars they circle. And if they are orbiting close by, their own light usually gets swamped.
But scientists want these images because there is so much to learn from them. Molecules within a planet's atmosphere absorb certain colors of light, so when astronomers study a planet's spectrum, they can look for what's missing from the rainbow to determine which gases — like water, methane, and carbon dioxide — are present in the planet's air. For the YSES-1 system, scientists not only saw molecules in the direct imaging but detected cloud particles and a dust disk.
On YSES-1c, rather than water vapor, the clouds are made of hot, ultra-fine rock grains. While Earth's clouds are often white and pillowy, these are probably hazy and dark, filling the sky with something akin to a glass powder. You can think of these silicate clouds sort of like the plumes of mineral ash that vent out of volcanoes.
YSES-1b is even "weirder," said Nasedkin, one of the coauthors. Around it is a so-called circumplanetary dust disk that could serve as a birthplace for moons, similar to those seen around Jupiter. Scientists used computer models to figure out that the dust is hot — about 400 to 600 degrees Fahrenheit.
Because this particular disk is much older than two previously found around other unrelated exoplanets, what is creating or sustaining it is a mystery. The original disk of planet-building material around the star is long gone, so the researchers have ruled that out as the source.
"It's possible that we're seeing the dust emitted by collisions of moons and other small, rocky bodies left over from the planet's formation!" Nasedkin said.
