A long-lost moon may explain the peculiar characteristics of Mars compared to the other rocky planets in the Solar System.
Mars currently has two small moons, but a larger moon in the past may have played a role in shaping the planet’s extreme landscape, according to a study by astronomer Michael Efroimsky of the US Naval Observatory.
Submitted to the Journal of Geophysical Research: Planets, the paper describing the research is available on the online preprint repository arXiv. The study suggests that this ancient moon, called Nerio, would have significantly influenced Martian topography.
A mosaic of Mars made up of about 100 images from NASA’s Viking satellite. The images were taken in 1980 during the mid-northern summer on Mars. Image credit: NASA/JPL-Caltech/USGS
Gravity of the lost moon Nerio disturbed the terrain of Mars
Mars has some of the most extreme terrain in the Solar System, including the highest mountain, the largest canyon, and vast highlands. The Tharsis bulge, for example, is an area 3,000 miles (5,000 km) wide and over 4 miles (7 km) high, with towering volcanoes rising even higher than that. Almost on the opposite side of the planet is another highland region, Terra Sabaea, and the shield volcano Syrtis Major.
Efroimsky proposes that Nerio’s gravity deformed Mars, creating “tides” in the magma oceans in a similar way to how Earth’s Moon causes ocean tides. However, because Mars is smaller than Earth, it cooled much more quickly, and its tidal bulges were trapped in the planet’s resulting shape.
Artist’s impression of Mars and its two moons, Deimos (above) and Phobos. New research suggests that a third moon, now lost, may have influenced the formation of the Martian surface. Credit: DLR
Nerio, in turn, would have disappeared somehow. It may have been destroyed by a collision, giving rise to the current moons Phobos and Deimos, or it may have been thrown out of the solar system by a gravitational interaction.
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Hypothesis raises questions and requires further investigation
Such collision and dispersion events were common in the early Solar System. For example, it is believed that Earth formed its Moon after an impact with a Mars-sized protoplanet. Similarly, Nerio could have existed long enough to shape the Martian landscape before disappearing.
Efroimsky admits, however, that Nerio’s hypothesis raises many questions, such as the absence of craters that should have been left by the moon during its orbit. He suggests that later geological processes may have erased these marks, and concludes by urging other scientists to explore ways to find evidence of this lost ancient Martian satellite.
