Ocean Tides on Asynchronously Rotating Planets Orbiting Low-mass Stars

Abstract Planets in the liquid-water habitable zone of low-mass stars experience large tidal forces, 10 3 –10 4 times those on Earth, due to the small distance between the habitable zone and the host stars. Therefore, interior solid tides, ocean tides, and atmospheric tides on these planets could be much stronger than those on Earth, but little work has been done to explicitly simulate the ocean tides. Here, for the first time, we perform global ocean tide simulations and show that ocean tides on asynchronously rotating planets with large eccentricities can reach <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi class="MJX-tex-calligraphic" mathvariant="script">O</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mn>1000</mml:mn> <mml:mo stretchy="false">)</mml:mo> <mml:mspace width="0.25em"/> <mml:mi mathvariant="normal">m</mml:mi> </mml:math> in height and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi class="MJX-tex-calligraphic" mathvariant="script">O</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mn>10</mml:mn> <mml:mo stretchy="false">)</mml:mo> <mml:mspace width="0.25em"/> <mml:mi mathvariant="normal">m</mml:mi> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">s</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> in flow speed. Interactions between tide and bottom topography can induce large energy dissipation, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>∼</mml:mo> <mml:mi class="MJX-tex-calligraphic" mathvariant="script">O</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mn>100</mml:mn> <mml:mo stretchy="false">)</mml:mo> <mml:mspace width="0.25em"/> <mml:mi mathvariant="normal">W</mml:mi> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">m</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:math> in the global mean. This tidal energy dissipation can strongly accelerate orbital evolution by 1–2 orders of magnitude. However, for planets with small eccentricities, the ocean tides are much weaker but still comparable to those on modern Earth. Our results suggest that ocean tides on eccentric planets orbiting low-mass stars are orders of magnitude more powerful than those on Earth and can dramatically influence surface geography and orbital evolution.