First-Ever 3D Structure of an Exoplanet's Atmosphere

For the first time, scientists have successfully mapped the three-dimensional structure of an exoplanet's atmosphere. Using all four telescopic units of the Very Large Telescope (VLT) operated by the European Southern Observatory (ESO) in Chile, researchers have analyzed the layered composition of WASP-121b, also known as Tylos, revealing distinct chemical stratification and extreme atmospheric winds.

Until now, scientists could determine the chemical composition of exoplanet atmospheres but lacked the ability to map their vertical structure or understand how different elements were distributed within them.

An Ultra-Hot Jupiter with a Unique Atmospheric Composition

WASP-121b belongs to a category of exoplanets known as **"ultra-hot Jupiters"**—massive gas giants that orbit extremely close to their host stars, making them scorchingly hot. Like Jupiter, its atmosphere is primarily composed of hydrogen and helium, but beyond that, WASP-121b's atmosphere is unlike anything seen before.

Researchers have identified three distinct layers in its atmosphere:

1. Lower layer – Contains gaseous iron, heated to the point where it remains in vapor form.
2. Middle layer – Characterized by the presence of sodium.
3. Upper layer – Mainly composed of hydrogen, with some of it escaping into space.

"This structure has never been observed before and contradicts existing theoretical models of how atmospheres should behave," explains Julia Victoria Seidel, an astronomer at the European Southern Observatory and the Lagrange Laboratory at the Observatory of the Côte d'Azur in France. Seidel is the lead author of the study published this week in the journal Nature.

Unexpected Discovery: Titanium in the Atmosphere

In addition to iron, scientists also detected titanium in gaseous form. On Earth, both iron and titanium exist only in solid form due to significantly lower temperatures. The presence of these metals in WASP-121b’s atmosphere highlights the extreme conditions of this exoplanet.

Located 900 light-years away from Earth, WASP-121b completes one orbit in just 1.3 days. The planet's day side reaches 2,700°C (4,892°F), while the night side maintains a scorching 1,250°C (2,282°F).

What This Means for Exoplanet Research

The ability to map atmospheric structures on exoplanets could be crucial in the search for planets that could potentially support life.

"Studies like this are essential to understanding our place in the universe," said Seidel. "Is Earth's climate unique? Can the models we create based on our own planet explain the diversity of exoplanets across the galaxy?"

"Our research demonstrates that climates can behave in ways that differ significantly from current predictions," she added. "There is far more diversity in planetary atmospheres than we have ever imagined."