Sedimentary rocks in Mars' Gale crater suggest the planet once had a much larger moon capable of generating tides in its ancient lakes. Researchers analyzed layered formations imaged by NASA's Curiosity rover, proposing this moon was 15 to 18 times the mass of current moon Phobos. While the idea revives tidal theories, some experts question whether the small crater lakes could support such activity.
Scientists have uncovered potential signs that Mars possessed a substantial moon in its distant past, one powerful enough to influence tides on the planet's surface waters. This hypothesis stems from an examination of sedimentary rocks in Gale crater, a 154-kilometer-wide site explored by NASA's Curiosity rover. The rocks feature alternating layers of varying thickness and color, known as rhythmites, which indicate periodic deposition likely driven by tidal forces.
Suniti Karunatillake of Louisiana State University, along with colleagues Priyabrata Das and Ranjan Sarkar, studied these formations. Their analysis revealed thin, dark lines resembling "mud drapes" formed when tides recede, closely mirroring patterns seen in Earth's tidal deposits. Using a Fourier transform, Sarkar identified rhythmic variations in layer thicknesses that align with influences from both the sun and a moon, supporting the presence of tidal activity.
The inferred moon would have been 15 to 18 times more massive than Phobos, Mars' largest current satellite, though still far smaller than Earth's moon—hundreds of thousands of times less so. The planet's two present moons, Phobos and Deimos, might represent fragments of this lost body. Karunatillake's team plans to present their findings at the American Geophysical Union meeting in New Orleans next week.
This builds on a 2023 suggestion by Rajat Mazumder of the German University of Technology in Oman, who noted similar layers in Jezero crater imaged by NASA's Perseverance rover. Mazumder views such rhythmites as "a very robust proof of tidal activity" on Earth, implying marine conditions on ancient Mars.
Skeptics remain cautious. Nicolas Mangold of the Laboratory of Planetology and Geosciences in France argues that Gale and Jezero's lakes were too small for significant tides, even with a larger moon. Christopher Fedo of the University of Tennessee, involved with Curiosity, suggests the layers could result from fluctuating river inputs rather than tides. Sarkar counters that hydrological connections, possibly through subsurface porosity in Mars' fractured terrain, might have linked larger water bodies to these craters, enabling tidal effects.