A young progenitor for the most common planetary systems in the Galaxy

Area of Science:

• Exoplanetary science
• Stellar astrophysics
• Planetary formation and evolution

Background:

• The Milky Way commonly features Earth-to-Neptune-size planets in compact orbits.
• Larger planets are rare at small orbital separations.
• The young star V1298 Tau hosts an unusual compact system with four large planets (5-10 Earth radii).

Purpose of the Study:

• To characterize the V1298 Tau planetary system using transit-timing variations.
• To determine the masses and orbital parameters of all four planets.
• To understand the formation and evolutionary history of these large, low-density planets.

Main Methods:

• Conducted a multi-year observational campaign using transit-timing variations.
• Utilized targeted observations to resolve the orbital period of the outermost planet.
• Combined new data with archival observations over a 9-year baseline for robust analysis.

Main Results:

• Resolved the orbital period of the outermost planet in the V1298 Tau system.
• Determined low, sub-Neptune masses and nearly circular orbits for all four planets.
• Observed large radii and low densities for the inner planets, suggesting rapid post-disk cooling.

Conclusions:

• The V1298 Tau planets likely experienced a dynamically tranquil history.
• Their current low densities indicate significant post-formation evolution.
• These planets are predicted to contract into the super-Earth/sub-Neptune size range observed commonly in the galaxy.