Webb found a planet where it 'rains sand' and another where 'sandcastles' are forming

The James Webb Space Telescope just caught two young planets throwing sand into their own skies. Its view of the YSES‑1 system, roughly 300 light‑years away in the constellation Musca, shows silicate grains swirling through alien atmospheres and settling into a dusty ring that looks like a newborn “sandcastle.”

Valentina D’Orazi of Italy’s National Institute for Astrophysics said the find rewrites how astronomers picture early gas‑giant weather.

“We are watching history in real time,” she said, “because every sand grain tells us how planets grow and trade material with their disks.” D’Orazi is an INAF astronomer who was on the discovery team.

Webb finds a sand pit at YSES‑1

The star YSES‑1, also known as TYC 8998-760-1, is only 16.7 million years old, about 400 times younger than the Sun. Its youth gives scientists a snapshot of gas giants that are still assembling their final bulk.

Planet “C” tips the scale at fourteen Jupiters and glows deep red because silicate clouds trap heat high in the air. Those clouds contain pyroxene and forsterite, the same minerals found in many meteorites on Earth.

Sibling planet “B” sits farther out and continues to gather material from a dusty circumplanetary disk, a flattened ring of sand‑rich gas that feeds the growing world.

Webb’s Mid‑Infrared Instrument (MIRI) resolved the disk’s own silicate signal, marking the first time grains were observed in both a planet and its surrounding nursery.

What sand clouds tell us

Sand in the sky sounds exotic, yet similar grains hide inside warmer brown dwarfs and some “hot Jupiters.” Earlier Webb studies caught sand particles on the gas giant WASP‑17 b.

In these super‑heated atmospheres, rock minerals behave the way water does on Earth. They vaporize near the interior, rise, cool, and then condense into tiny crystals that float like high cirrus clouds.

Each sand crystal measures less than four‑ten‑thousandths of an inch, yet collectively they redden the planets and block outgoing heat. That blanket slows cooling, so the worlds stay puffier for longer than textbook models predict.

YSES‑1 planet building its own sandcastle

Planet b’s disk glitters with sub‑micron olivine dust that has been created by grinding collisions among moon‑sized building blocks.

Because the ring orbits roughly eight times farther from its star than Neptune does from the Sun, Webb could separate starlight from planetary glow and isolate the dust spectrum.

The team nicknamed the disk a “sandcastle” since its material may clump into moons the way Saturn’s rings nurture shepherd satellites.

If that happens, the moons could carry the same silicate signature, offering future missions a clean target for composition checks.

Lessons about Jupiter and Saturn

Gas giants in our own neighborhood likely passed through similar dusty stages, but their ancient debris is long gone.

Comparing YSES‑1 to the middle‑aged Jupiter may clarify why our planet retains heavy elements in some layers and not others.

“Examining these planets is like peeking into the history of our own planetary back yard,” D’Orazi noted. The statement echoes earlier ideas drawn from brown dwarf VHS 1256 b, whose sand storms were logged by Webb in 2023.

By measuring grain size and altitude, researchers can map vertical mixing, the process that stirs gases, drives weather, and fixes the final menu of molecules that telescopes detect in mature planets.

Such context is critical when teams search for biosignatures, because haze thickness can hide or mimic life‑related gases.

How to find sand on distant planets

Webb used spectroscopy, the art of splitting light into colors, to spot the tell‑tale 9–11 micron dip caused by silicates. That fingerprint matched models developed from earlier observations of brown dwarfs with silicate hazes.

Because planets b and c orbit five to ten Neptune‑Sun distances from their star, the glare was low enough for direct imaging.

MIRI captured about two hours of data per target, then staff at the European JWST Science Operations Center ran a custom pipeline to weed out cosmic‑ray hits and residual star light.

The resulting spectra show particle sizes under 0.1 micron at pressures of one‑thousandth of Earth’s sea‑level.

Such fine grains stay aloft for years before clumping and sinking as “sand rain,” a process inferred on the fluffy world WASP‑107 b last year.

Weather forecasts on exoplanets

Follow‑up time with Webb and the future Extremely Large Telescope will monitor seasonal changes in the sand clouds on these planets.

If the grain layer thins, temperatures should drop and methane bands may emerge, tightening estimates of planetary age.

The team also hopes to catch flashes of lightning inside the clouds, a phenomenon predicted for silicate sand storms but never confirmed.

Detecting such bursts would reveal how mineral clouds electrify, an analog to dust devils that charge Martian air.

Closer to home, Jupiter’s Great Red Spot shows little sand but plenty of ammonia ice. Comparing its dynamics to the sand storms of YSES‑1 could expose universal rules that apply across a hundred‑fold temperature range.

Every new Webb dataset reminds researchers that exoplanet weather resists simple, one‑size‑fits‑all descriptions.

Still, by matching color, grain chemistry, and disk mass, astronomers inch toward models that no longer treat distant planetary giants as blank, featureless spheres.

The study is published in Nature.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–