Atmospheric limb of WASP-17 b reveals significant temperature differences

Researchers have mapped the three-dimensional atmospheric structure of the hot Jupiter WASP-17 b. By observing the planet as it transits its star, the data reveals a stark 650 Kelvin temperature difference between the planet's morning and evening limbs. These results provide new insights into the complex dynamics and chemical distribution within the atmospheres of giant gas planets orbiting distant stars.

Star system: WASP 17 | Distance from the Sun: 1315 light years

Planets are complex three-dimensional objects where heat and motion play critical roles in shaping their environments. While scientists have previously focused on mapping the dayside of exoplanets, new methods now allow for a more detailed look at the atmosphere around the planet's limb - the outer edge visible as the planet passes in front of its star. By applying a technique called transmission strings to observations of the hot Jupiter WASP-17 b, the study reveals how temperature and chemical composition vary across different sections of its atmosphere.

The mapping method captures light over a wide range of wavelengths, from 0.6 to 12 micrometers, allowing for an analysis of both east-to-west asymmetries and equator-to-pole variations. This approach provides a comprehensive view of the atmosphere by measuring the thermal scale height, which is a measure of how the density and temperature of the atmosphere change with altitude. The results correlate well with previous measurements of the planet's nightside emission and dayside eclipse mapping, confirming a consistent picture of the planet's global climate.

Beyond temperature variations, the data also provides information on the chemical makeup of the atmosphere. The abundances of water vapor and carbon dioxide remain constant around the limb. These findings offer a direct way to test global circulation models, which are theoretical simulations used to predict how winds and heat move through a planet's atmosphere. By providing these specific observational constraints, the findings help refine our understanding of how gas giants function on a planetary scale.

Key findings
WASP-17 b exhibits a morning temperature of 858 Kelvin and an evening temperature of 1522 Kelvin.
The atmosphere shows a clear transition in thermal scale height across the limb.
Abundances of H2O and CO2 remain consistent across the observed limb of the planet.
The transmission string technique maps 3D atmospheric variations from equator to pole.

Scientific study

A Spatial Map of the Atmospheric Limb of a Hot Jupiter (external link)