Mars may once have had a much larger moon

A crater on Mars may once have contained water that sloshed back and forth as the tides ebbed and flowed. If this is true, then it follows that Mars must have had a moon massive enough to exert enough gravitational pull on the planet's seas to create tides. Neither of the two moons it currently possesses is large enough for the job.

Suniti Karunatillake from Louisiana State University and his colleagues found that traces of tidal activity appear to be preserved in thin layers within the sedimentary rocks of Gale Crater.

They analyzed layers of sediment to determine the timing of the tides and the properties of the moon that contributed to their occurrence. If it did exist, it would be 15 to 18 times more massive than Phobos, the largest of the Red Planet's two current moons. That would still make it hundreds of thousands of times less massive than Earth's Moon. Two of today's Martian moons may actually be the remnants of a larger moon.

Karunatillake will present the team's results at the team's annual meeting next week. American Geophysical Union in New Orleans, Louisiana.

The stones on which the researchers based their conclusions were photographed NASA Curiosity all-terrain vehicle. They contain alternating layers of different thicknesses and colors. Such layers are called rhythmites because they are a sign that the material was carried by wind or current with regularly varying strength. In the case of high tides, the incoming tide brings sand, which is then covered with fine mud when the tide turns and the water stops.

Gale's rhythms contain thin, dark lines reminiscent of such “mud sheets” that “show a very close resemblance to Earth's tides,” says team member Priyabrata Das, also of Louisiana State University.

To strengthen the team's hypothesis, Ranjan Sarkar The Max Planck Institute for Solar System Research in Germany used a standard mathematical method called the Fourier transform to analyze the structure of layers of Martian rocks. This revealed additional periodicity in the thickness of the layers, suggesting that both the Sun and Moon once controlled the tide, just as they do on Earth.

With this analysis, the researchers may have confirmed an idea first proposed by Rajat Mazumder at the German University of Technology in Oman. An expert on rhythmites, he suggested in 2023 that the layered formations observed by NASA's Perseverance rover in another Martian crater, Jezero, may be tidal. But these images did not have enough resolution for Fourier transform. Encouraged by Gale's analysis of rhythmites, Mazumder notes that the discovery of such rhythmites on Earth “is very strong evidence for tidal activity. In other words, sea conditions.”

But not everyone is convinced of this. The lakes inside the Jezero and Gale craters, with diameters of 45 and 154 kilometers respectively, were too small for tides to occur, he says. Nicholas Mangold at the Laboratory of Planetology and Geosciences in Nantes, France, who is a member of NASA's Perseverance Mars team. “So even though the moon was larger in the past, I don't think these two locations are suitable for recording tidal deposits.”

Christopher Fedo from the University of Tennessee, who is working with NASA on Curiosity research, also sees problems with the idea of ​​a larger Moon and notes that tidal rhythms could form as a result of regularly changing river inflows into a lake.

But Sarkar thinks there may be a way out for the tidal interpretation. “It is possible that the ocean was hydrologically connected to Gale. Even subsurface porosity can connect bodies and cause tides. On Mars, the surface is highly fractured and cratered, so porosity is not a problem there.”