Prospects for detecting the Rossiter–McLaughlin effect of Earth-like planets: the test case of TRAPPIST-1b and c

The Rossiter–McLaughlin effect is the principal method of determining the sky-projected spin–orbit angle (β) of transiting planets. Taking the example of the recently discovered TRAPPIST-1 system, we explore how ultracool dwarfs facilitate the measurement of the spin–orbit angle for Earth-sized planets by creating an effect that can be an order of magnitude more ample than the Doppler reflex motion caused by the planet if the star is undergoing …