Spectroscopy reveals atmospheric differences in hot Jupiters and Neptunes near the Neptune desert

Star system: WASP-50 | Distance from the Sun: 594 light years

Hot Jupiters and ultra-hot Jupiters are gas giant planets that orbit very close to their stars, making them excellent targets for atmospheric studies. This research examined five such planets—WASP-50b, WASP-117b, WASP-156b, WASP-167b, and WASP-173Ab—using high-resolution spectroscopy to search for atmospheric signals. These planets are located near the so-called Neptune desert, a region where Neptune-sized planets are rare at short orbital periods.

The study found no significant atmospheric absorption signals in the three denser, less-inflated hot Jupiters (WASP-50b, WASP-156b, and WASP-173Ab). In WASP-117b, hydrogen and lithium were marginally detected, while in WASP-167b, hydrogen and iron were tentatively detected, with iron showing a strong, blue-shifted signal. Atmospheric retrieval for WASP-167b revealed the presence of several metals and an equilibrium temperature. The comparison between WASP-173Ab and WASP-167b, both ultra-hot Jupiters, suggests a possible transition in atmospheric properties between 1900 and 2300 K. These results help clarify how atmospheric composition and temperature relate to planet type and position near the Neptune desert.

Key findings
- Five hot and ultra-hot Jupiters near the Neptune desert were studied with high-resolution spectroscopy
- No strong atmospheric signals were found in the denser, less-inflated planets
- WASP-117b shows marginal detections of hydrogen and lithium
- WASP-167b shows tentative detections of hydrogen and iron, with iron strongly detected and blue-shifted
- Results suggest a transition in atmospheric properties for ultra-hot Jupiters between 1900 and 2300 K

Scientific study

High-resolution spectroscopic atmospheric studies of 5 hot Jupiters across the edge of the Neptune desert (external link)