When you look up on a cold winter day and see bright spots of light flanking the sun—called sun dogs—you’re witnessing the beautiful result of ice crystals aligning just right in Earth’s atmosphere.
Other shimmering effects, like halos or light pillars, can also appear when sunlight interacts with these well-ordered crystals.
Now, astronomers say something similar could be happening light-years away—on a planet with clouds made not of water, but of quartz crystal.
Scientists at Cornell University have discovered that conditions in the atmosphere of a distant exoplanet, WASP-17b, could give rise to celestial light shows that resemble Earth’s sun dogs.
But instead of ice, the skies there could be filled with windswept crystals of minerals like quartz, creating dazzling visual effects as they interact with starlight.
WASP-17b is a “hot Jupiter”—a type of giant, gas-filled planet that orbits very close to its star, resulting in extremely high temperatures and fierce atmospheric winds.
These winds can reach speeds of 10,000 miles per hour. According to Elijah Mullens, a Cornell doctoral student and co-author of the study, winds this strong could line up tiny, boat-shaped crystals like a fleet of canoes in a raging river.
The study, titled Silicate Sundogs: Probing the Effects of Grain Directionality in Exoplanet Observations, was published July 21 in The Astrophysical Journal Letters.
Mullens worked with Professor Nikole Lewis, an expert in exoplanet atmospheres, to explore how fast-moving winds could mechanically align these crystal particles—a process first suggested back in 1952 by Cornell astronomer Tommy Gold.
Gold’s idea, called mechanical alignment, suggested that moving gas could force dust particles into specific directions. While that idea no longer applies to dust in the vast spaces between stars, Lewis believes it could be the perfect explanation for what’s happening in the dense, fast-moving atmospheres of hot Jupiters.
This new insight follows a surprising discovery the team made in 2023 while using NASA’s James Webb Space Telescope (JWST). They found signs of quartz nanocrystals in WASP-17b’s high-altitude clouds—something they never expected in such an extreme environment. Each of these crystals is just 10 nanometers wide—so small that 10,000 could line up across a human hair.
Though we can’t photograph WASP-17b directly—it’s 1,300 light-years away—JWST allows researchers to detect how its atmosphere interacts with light. If we could take a picture of the planet’s disk with an optical camera, Lewis says, we might see glowing features like sun dogs there too.
Aside from looking stunning, these effects provide clues about the exoplanet’s atmosphere, Mullens explains. The way crystals align tells scientists about the forces acting on them—whether it’s wind, electric fields, or something else. These light patterns, much like on Earth, offer valuable insight into the weather and chemistry of alien skies.
Mullens isn’t done yet. He’s leading a new JWST project to study particle alignment on WASP-17b more closely in the coming year.
The ultimate goal: to learn how light behaves in faraway worlds—and what it can teach us about their strange and beautiful atmospheres.
Source: Cornell.
