Were There Tides on Ancient Mars?

Abstract Tides are a key component in the Earth system as they help regulate climate and sustain life. Mars very likely had a surface ocean around 4–3 billion years ago. The NASA Curiosity Rover and the CNSA Zhurong Rover were sent to Gale Crater and the Vastitas Borealis Formation (VBF) on Mars to explore the surface and search for evidence of the past presence of water. Both rovers have since documented sedimentary rocks with features interpreted as deposited by tides. These include oppositely dipping cross‐laminations and cross‐stratifications, as well as bundled cross‐stratifications with systematic patterns, reactivation surfaces and mudstone drapes. To determine if tides on Mars had the capacity to transport sediment and form these structures, Martian tides were simulated using a numerical tidal model. Because the Martian moons are too small to generate a tide, the focus was on the solar tide. The resulting tidal current speeds were used in a Shields curve, modified to take into effect the lower gravity on Mars, to evaluate the sediment transport capacity of the tidal currents. The maximum current speeds at both rover locations are less than 0.01 m s −1 , below the calculated threshold for the movement of silt, and thus dispute the interpretation that the sedimentary features seen by the Zhurong Rover are tidal in origin and agree with previous interpretations that the Gale Crater was a paleo‐lake. However, there are other areas of the planet where tides may have had the energy necessary to form tidal deposits.