A vanished moon could explain why Mars is so different from the other rocky planets in our solar system.
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Today, Mars has two tiny moons. But early in its history, the Red Planet may have had a much larger moon, which could account for its odd shape and extreme terrain, suggests Michael Efroimsky, an astronomer at the U.S. Naval Observatory in Washington. His research has been submitted to the Journal of Geophysical Research: Planets and is available as a preprint via arXiv.
Mars is home to some of the most extreme terrain in our solar system, including the largest canyon, the tallest mountain, and the largest mountain range. This mountainous region, known as Tharsis, dominates the western hemisphere of Mars near equator . The Tharsis region is about 5,000 kilometers wide and rises up to 7 km in height, excluding its massive volcanoes, which rise even higher. Almost exactly on the opposite side of the planet from Tharsis are Terra Sabaea and Syrtis Major, another mountainous region and a massive volcano , respectively.
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It is believed that Nerio's significant mass changed the shape of Mars with its gravity, increasing tides in the magma oceans in the same way that Earth's moon increases tides in our planet's oceans today. But because Mars is smaller than Earth ,it cooled much more quickly, and its tidal bulges were locked into the planet's resulting shape.
Somehow, Nerio got lost, Efroimsky argues. It could have been obliterated by a collision, leaving behind the present-day Martian moons Phobos and Deimos, or it could have been swept out of the solar system through a gravitational interaction with another body.
Such collisions were common in the early solar system. Astronomers believe that Earth acquired its moon through a collision with a Mars-sized protoplanet, and the scatterings between the outer planets shifted their original orbits, which were once much closer to the sun, to their current positions.
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While the possibility is intriguing, Efroimsky admitted that the Nerio explanation is just a hypothesis. The idea of a large moon that existed for a short time raises many questions, especially regarding its formation and eventual disappearance. For example, if the moon Nerio was destroyed, it should have left a series of craters along the belt aligned with its orbit, but there is no such series of craters on Mars. On the other hand, further collisions and geological activity could have obliterated these traces.
Source: livescience
