TOI-5322 b orbits an ancient star in the milky way thick disk

Analysis of host stars reveals that the hot Jupiter TOI-5322 b belongs to the ancient, chemically distinct thick disk population of the Milky Way. By comparing stars across different galactic regions, researchers identified key differences in the mass and orbital periods of giant planets depending on their home environment, providing new insight into how these planetary systems evolve over billions of years.

Star system: WASP-81 A | Distance from the Sun: 1313 light years

The planet TOI-5322 b is a hot Jupiter, a large gas giant planet that orbits extremely close to its parent star. Recent observations identify its host star as a member of the high-alpha thick disk of the Milky Way. This region consists of older, chemically distinct stars that formed in the galaxy long ago. By identifying planets within this ancient stellar population, researchers can better understand how different galactic environments influence the formation and long-term evolution of giant planets.

To determine the origin of these host stars, experts conducted a homogeneous analysis of 268 confirmed and candidate planetary systems. They utilized high-resolution spectra and precise measurements from the Gaia mission to assess the stellar temperature, surface gravity, radius, and chemical composition. By comparing the abundance of alpha elements relative to iron, they categorized the stars into the thin disk, the thick disk, or an ambiguous intermediate population.

Comparing these populations reveals that planets orbiting stars in the high-alpha thick disk and the ambiguous group differ from those in the standard thin disk. Notably, these ancient planets tend to be less massive than their counterparts in the thin disk. Additionally, none of the confirmed planets in the high-alpha or ambiguous groups have orbital periods shorter than 2.7 days, whereas 22 percent of the thin disk population does. These findings suggest that planet formation or orbital evolution may change significantly depending on the age and chemical environment of the host star.

Key findings
TOI-5322 b is confirmed to orbit a star in the ancient high-alpha thick disk of the Milky Way.
Planets in the thick disk population are generally less massive than the median hot Jupiter found in the thin disk.
High-alpha and ambiguous disk systems lack planets with orbital periods shorter than 2.7 days.
The studied systems are older than 8 billion years, offering a look at long-term planetary evolution.

Scientific study

A Sample of Thick-Disk Stars Hosting Hot Jupiters (external link)