Orbital architecture and spin-orbit alignment of the TOI-2134 planetary system

Star system: TOI 2134 | Distance from the Sun: 73.9 light years

The TOI-2134 planetary system contains two confirmed planets orbiting their host star. The inner planet is a mini-Neptune, a gas-rich world smaller than Neptune, while the outer planet is a temperate sub-Saturn. By combining new observations from the TESS space telescope with extensive ground-based velocity measurements, the composition and orbital paths of these planets have been precisely determined, revealing a complex system architecture.

The research confirmed that the inner planet completes an orbit in approximately 9.2 days, while the outer sub-Saturn takes about 95.8 days with a notably elliptical, or eccentric, path. Researchers also identified a long-term trend in the star's movement, which is attributed to a stellar magnetic cycle, a periodic change in the magnetic activity similar to the Sun's activity cycles.

To understand the system's history, the team measured the Rossiter-McLaughlin effect, which occurs when a planet transits a star and causes a shift in the perceived rotation of the stellar surface. This helped determine the spin-orbit alignment, revealing the angle at which the outer planet orbits relative to the star's equator.

Key findings
- TOI-2134 b is a mini-Neptune with a mass of 9.37 Earth masses and a radius of 2.73 Earth radii.
- TOI-2134 c is a temperate sub-Saturn with a mass of 58.3 Earth masses and a radius of 7.35 Earth radii.
- The outer planet follows an eccentric orbit with an eccentricity of 0.31.
- The outer planet shows a significant misalignment between its orbit and the star's rotation axis of 59 degrees.
- A long-term radial velocity trend suggests the host star undergoes a magnetic cycle.

Scientific study

Understanding eccentric temperate giants: an in-depth study of the architecture and stellar obliquity of the TOI-2134 system (external link)