Thick-disk stars identified as hosts to ancient hot jupiter planets

An analysis of 268 stars reveals new hot Jupiter planets orbiting within the Milky Way's ancient thick disk. These systems, over 8 billion years old, show key differences in planet mass and orbital distance compared to planets in the younger thin disk. These findings suggest that the galactic environment influences how massive gas giant planets form and evolve over vast timescales.

Star system: TOI-3118 | Distance from the Sun: 1410 light years

Large gas giant planets that orbit very close to their parent stars are known as hot Jupiters. By analyzing a sample of 268 stars, researchers have identified several hot Jupiters orbiting stars belonging to the high-alpha thick disk of our galaxy. The thick disk represents a component of the Milky Way containing older stars with specific chemical signatures, particularly higher amounts of alpha elements like magnesium, silicon, and calcium relative to iron. These systems are significantly older than the Sun, with estimated ages exceeding 8 billion years.

To categorize these stars, the team combined high-resolution spectra with distance and brightness data from the Gaia, 2MASS, and WISE space missions. This data allowed them to precisely determine stellar temperatures, sizes, surface gravity, and chemical compositions. By comparing these markers, they classified the host stars into the high-alpha thick disk, the low-alpha thin disk, or an intermediate population. This classification helps distinguish the varied environments where planetary systems across the galaxy formed.

The findings reveal notable differences in the properties of hot Jupiters based on their galactic origin. Planets found around high-alpha thick-disk stars and those in the intermediate population tend to have lower masses than their counterparts in the thin disk. Furthermore, none of the confirmed planets in the high-alpha or intermediate groups have orbital periods shorter than 2.7 days, whereas 22 percent of the thin-disk population do. These differences suggest that giant-planet formation and long-term orbital evolution may be influenced by the chemical and evolutionary history of their specific galactic neighborhoods.

Key findings
Confirmed hot Jupiters WASP-81 b and TOI-5322 b reside in the high-alpha thick disk.
Three candidate planets, TOI-3118.01, TOI-2728.01, and TOI-5781.01, are identified as thick-disk members.
Thick-disk hot Jupiters are typically less massive than those found in the thin disk.
No planets around thick-disk or intermediate stars were found with orbital periods shorter than 2.7 days.
These ancient systems are older than 8 billion years, providing a long-term view of planet evolution.

Scientific study

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