Alien suns reversing in exoplanet skies

Area of Science:

• Planetary Science
• Exoplanetary Science
• Astrodynamics

Background:

• Earth's consistent eastward solar motion is due to its spin, tilt, and orbit.
• Unusual solar motion, including apparent reversals, can occur on exoplanets and even Mercury.
• Understanding solar motion is crucial for characterizing exoplanetary environments.

Purpose of the Study:

• To investigate the conditions and scope of apparent solar motion reversals on exoplanets.
• To analyze how orbital and spin parameters influence solar motion.
• To develop a generalized concept of a solar day for various planetary scenarios.

Main Methods:

• Studying solar motion as a function of eccentricity, spin-orbit ratio, obliquity, and nodal longitude.
• Visualizing planetary motion using spatial and spacetime plots.
• Deriving nonlinear equations to define boundaries for reversing and non-reversing solar motion.

Main Results:

• Solar motion reversals occur when a planet's spin angular speed falls between its maximum and minimum orbital angular speeds (at zero obliquity).
• Exact nonlinear equations were derived to quantify the conditions for reversing and non-reversing solar motion.
• The study provides a framework for understanding and visualizing complex solar motion patterns.

Conclusions:

• Apparent solar motion reversals are possible on exoplanets under specific spin-orbit dynamics.
• The derived equations provide precise bounds for predicting such phenomena.
• A generalized solar day concept is proposed to accommodate these reversals, enhancing exoplanetary observation analysis.