Webb maps the lopsided atmosphere of puffy planet WASP-17b
WASP-17b（WASP seventeen b）
The distant planet studied in this research.
transmission strings
A method that measures an atmosphere's edge at many angles.
hot Jupiter
A large gas planet that orbits very close to its star.
What happened
Astronomers mapped the atmosphere of WASP-17b around its visible edge. They used the James Webb Space Telescope, or JWST, a space observatory for studying distant light. WASP-17b is an exoplanet, a planet beyond our solar system. The study appeared in Nature Astronomy on October 14, 2026. News reports called protruding atmospheric regions 'gemstones.' The team did not photograph actual jewels. The phrase describes places where the atmosphere rises farther out. See Space.com.
Why this planet is unusual
WASP-17b is a hot Jupiter, a large gas planet orbiting close to its star. It lies about 1,300 light-years away. Its radius is about 1.9 times Jupiter's radius. Its mass is about half Jupiter's mass. Its equilibrium temperature is about 1,760 kelvins. It completes an orbit in about 3.7 days. One side permanently faces the star. That creates a constantly lit dayside and a darker nightside. Heat and winds can therefore change the atmosphere around the planet.
How the map works
During a transit, the planet crosses in front of its star. Some starlight passes through the atmosphere's edge. Molecules absorb specific wavelengths. Those missing colors reveal parts of the atmosphere. Older analyses averaged the whole edge. They also treated it as a circle with one radius. The new transmission strings method fits the radius at many angles. It can compare the morning and evening sides. It can also examine changes from the equator toward the poles. The team used JWST transit data from three instruments. The data covered wavelengths from 0.6 to 12 micrometers. The observations were collected in March 2023.
What the team confirmed
The morning side was estimated at about 858 kelvins. The evening side was about 1,522 kelvins. The difference was about 650 kelvins. The warmer evening atmosphere had a larger vertical extent. Models predict heat-carrying winds from the dayside. Those winds reach the evening equator after crossing the nightside. The observed shape matched that broad prediction. Water vapor and carbon dioxide also stayed broadly consistent around the edge. Other observations of the dayside and nightside supported the temperature pattern.
Why it matters
This is more than a better-looking planet picture. It demonstrates a way to extract location-based information from a transit. Researchers can move beyond one average spectrum. They can ask how heat, chemistry, and clouds change around a world. The result is an important step toward studying exoplanet weather in three dimensions. It also tests whether circulation models describe real planets.
What remains uncertain
The study is not a complete weather report. The analysis assumed north and south were broadly symmetrical. The method needs very strong signals. It uses lower spectral resolution and larger uncertainties than standard averages. The team could reliably constrain water and carbon dioxide. It could not firmly map every gas or aerosol. The exact wind speeds and cloud-particle patterns remain uncertain.
What to watch next
Future JWST observations should improve measurements beyond five micrometers. They may clarify how clouds and particles vary around the edge. Researchers also want to apply transmission strings to other exoplanets. The key question is whether WASP-17b's lopsided atmosphere is common or unusual. The original paper is available in Nature Astronomy, and the University of Bristol provides a plain-language explanation.
Why one side of a faraway planet looks puffier
📰 Full story: Webb maps the lopsided atmosphere of puffy planet WASP-17b
A new method shows how WASP-17b changes around its edge.
exoplanet
A planet that orbits a star beyond our solar system.
limb
The outer edge of a planet's atmosphere.
transmission strings
A method for measuring an atmosphere's edge in separate places.
💡 The gist
- The James Webb Space Telescope studied WASP-17b, a distant planet.
- One side of its atmosphere was hotter and larger.
- A new method revealed the uneven shape.
What is WASP-17b?
WASP-17b is an exoplanet. An exoplanet is a planet beyond our solar system. It is also a hot Jupiter. That means it is a large gas planet near its star. WASP-17b is almost twice Jupiter's radius. Yet it has about half Jupiter's mass. Its air is very spread out. The planet circles its star in about 3.7 days. One side always faces the star. The other side stays away from starlight.
How did Webb see the air?
The planet passed in front of its star. Some starlight crossed the planet's atmosphere. Different gases change different colors of light. Scientists read those changes for clues. The atmosphere's edge is called the limb. Older methods averaged the whole limb. They treated it as one smooth circle. The new transmission strings method checks many points. It measures how far the edge reaches at each angle. This creates a more detailed map.
Scientists used several Webb instruments. Their data covered infrared light from 0.6 to 12 micrometers. That range helped them compare water and carbon dioxide signals. The observations came from March 2023.
Why was one side bigger?
The star heats the planet's dayside. Strong winds carry heat around the planet. The evening edge stays warmer than the morning edge. The difference was about 650 kelvins. A warmer atmosphere spreads higher. So the evening edge sticks out farther. The team also found water vapor and carbon dioxide. Their amounts stayed fairly similar around the edge.
Why does this matter?
Scientists usually study an average atmosphere. This study separates different places around one planet. It gives clues about planetary weather. It also checks predictions from computer models. Still, this is not a complete weather picture. The team assumed the north and south sides matched. Clouds and some gases remain uncertain. More Webb observations may test other planets. Read the Nature Astronomy paper and the University of Bristol explanation.
A faraway planet has a puffy side
📰 Full story: Webb maps the lopsided atmosphere of puffy planet WASP-17b
WASP-17b's sky sticks out more on one side.
WASP-17b（WASP seventeen b）
A big planet far beyond our solar system.
James Webb Space Telescope
A large telescope in space that studies distant light.
atmosphere
The layer of air around a planet.
WASP-17b is a big planet far beyond our solar system. The James Webb Space Telescope is a giant telescope in space. It watched starlight pass around the planet's sky. That sky is the planet's atmosphere.
One side always faces the nearby star. That side gets the star's heat. Wind carries some heat around the planet. One edge becomes warmer and puffier. Scientists saw this through tiny changes in starlight.
Scientists did not find real gemstones. The word gemstones was a playful name for puffy spots. They also found water and carbon dioxide in the air. More watching may show other planets with lopsided skies.