The Teegarden Star system is composed of two Earth-sized planets orbiting a 0.08 solar-mass M dwarf star and is just 12 light years from Earth. Both planets are located in the habitable zone of their star, with Teegarden’s Star b near the inner edge and Teegarden’s Star c near the outer edge. Both planets tidally interact with their host star and close enough to that they significantly perturb each other’s orbits.
In such configurations, planetary obliquity can become locked at values greater than zero, a configuration known as a Cassini state. Since Teegarden’s Star b’s obliquity may be detectable via a JWST phase curve, we simulated the evolution of the system for its age with VPLanet over a wide range of plausible initial conditions to predict the possible values of their obliquity today. We find the final distribution of obliquities for both planets are confined to be less than 1°.
We further explored the tidal heating in the two planet and find that even this small obliquity can be enough to power a runaway greenhouse effect on planet b, possibly desiccating it. On planet c, the Cassini state may power Io-like volcanism. The Cassini states adds about 1 W/m² to the total tidal heating.