Outer giant planet in Pi Mensae system influences the orbit of planet d

Star system: Pi Mensae | Distance from the Sun: 59.6 light years

The Pi Mensae star system hosts a complex arrangement of planets, including a massive giant planet known as planet b, a small transiting sub-Neptune planet c, and a candidate planet d orbiting between them. New research examines how the gravitational influence of the outer giant planet b impacts the orbital path of the middle planet d, specifically focusing on its eccentricity, which describes how much an orbit deviates from a perfect circle.

By reanalyzing 772 velocity measurements of the host star, the analysis confirms that planet d maintains a high eccentricity, calculated at approximately 0.38. This means the planet follows a notably elongated path rather than a circular one.

Using computer-based N-body simulations, which track the gravitational interactions of multiple objects over time, researchers tested how these planets interact over tens of thousands to millions of years. The findings demonstrate that the outer giant planet exerts a continuous gravitational pull, or secular forcing, that naturally pushes planet d into this elongated orbit.

These simulations show that the system is most stable when planet d orbits in a near-coplanar arrangement, meaning it shares a similar orbital plane with the other planets, moving either in the same direction or opposite to the rotation of the system. Without this configuration, the complex gravitational dance would likely lead to orbital instability or even collisions with the host star.

Key findings
- Planet d possesses a high orbital eccentricity of approximately 0.38.
- Gravitational forcing from the giant planet b is responsible for exciting and maintaining the elongated orbit of planet d.
- Stable configurations for the system favor near-coplanar orbits for planet d.
- Simulations show that the influence of the outer giant planet allows for long-term orbital survival of up to 100 million years.

Scientific study

An Outer Giant Excites and Constrains the Orbit of π Mensae d (external link)