The Red Planet's Ancient Moon Mystery: Sedimentary Clues Unveiled
A recent study has revealed intriguing evidence of Mars' ancient past, suggesting the existence of a much larger moon than the two known moons, Phobos and Deimos. The research, presented at AGU's Annual Meeting 2025, focuses on thin layers of sedimentary rock found in Gale Crater, hinting at a significant gravitational influence on the planet's history.
The team, led by planetary scientist Ranjan Sarkar, analyzed images captured by the Curiosity rover's Mars Hand Lens Imager, revealing fine, repeating layers of light and dark colors. These layers, interpreted as tidal rhythmites, indicate the regular back-and-forth sloshing of tides, a phenomenon typically associated with larger moons.
Sarkar explains, 'Our study provides sedimentary evidence for the case of tidally deposited rhythmites, hinting at a past larger moon for Mars. This aligns with the hypothesis that Mars has repeatedly had larger moons that were tidally destroyed into rings, which then reformed into successively smaller moons.'
The layers were discovered at Vera Rubin Ridge, on the flank of Mount Sharp, a sedimentary peak in Gale Crater. The studied area, approximately 35 cm long and 20 cm thick, contained individual bands ranging from submillimeters to millimeters thick, with lighter and darker tones.
Bob Craddock, a geologist not involved in the study, notes that similar sedimentary layers can be formed by various processes, including winds, seasonal precipitation, or glacier melts. However, the team argues that the observed patterns are more consistent with tidal activity.
Suniti Karunatillake, a geologist and geophysicist, emphasizes the complexity of the analysis, stating, 'We can't be decisive, so our argument is one of consistency.' The team estimates that the layers were deposited with a monthly cycle of about 30 days, requiring a moon at least 18 times the mass of Phobos, orbiting at an altitude of about three times Mars' radius.
The study challenges the traditional theory of Phobos and Deimos as captured asteroids, suggesting that Mars may have had a larger moon that was tidally destroyed, forming the current moons. This hypothesis is supported by previous research, indicating that Mars may have experienced multiple such events.
The researchers plan to conduct a detailed celestial mechanics study to refine their estimates and examine other sites in Gale Crater for similar tidal rhythms. Any inconsistencies would challenge their model, but agreement among sites would strengthen the argument for an ancient large moon.
This discovery invites further exploration and discussion, as scientists continue to unravel the mysteries of Mars' ancient moons.
