Circular orbits show hot Jupiter's moved smoothly through disks

Astronomers reveal some hot Jupiters formed via smooth disk migration. (Image: Graduate School of Arts and Sciences/College of Arts and Sciences/The University of Tokyo)

Astronomers have uncovered new evidence explaining the origins of hot Jupiters. These giant planets orbit extremely close to their parent stars. Understanding their formation helps explain planetary system evolution across the galaxy. Researchers focused on over 500 known hot Jupiter exoplanets worldwide.

Traditionally, hot Jupiters were thought to form far from stars and migrate inward. Two main mechanisms exist: high-eccentricity and disk migration pathways. Disk migration moves planets gradually inward while maintaining circular orbital paths. This contrasts with high-eccentricity migration, which disturbs planetary orbits violently.

Researchers developed a new method calculating circularisation times for these planets. Around 30 hot Jupiters showed circular orbits inconsistent with high-eccentricity migration. These planets likely moved smoothly through their primordial protoplanetary disks. Their orbits remain aligned with the parent star’s rotation axis.

Aligned orbits suggest multiple planetary companions survived migration undisturbed. High-eccentricity migration would typically eject other planets from the system entirely. Disk migration preserves primordial system architecture and orbital stability. This insight helps scientists predict configurations of exoplanetary systems.

Studying atmospheric composition may reveal formation locations within protoplanetary disks. Elemental ratios could help differentiate disk migration from other migration mechanisms.

Observations with next-generation telescopes will expand understanding of close-in giant planets. These discoveries shed light on how planetary systems form and evolve over time.