Mars’s Unique Shape May Be Linked to a Long-lost Moon

Astronomers have long puzzled over Mars's unusual geography and triaxial shape. A new hypothesis by Michael Efroimsky of the U.S. Naval Observatory suggests that these distinct features might be due to a large moon that once orbited the Red Planet. This lost moon, named Nerio, may have dramatically influenced Mars's formation and landscape.

Mars’s Triaxial Shape: A Planetary Mystery

One of the more peculiar aspects of Mars is its triaxial shape, where the planet's dimensions vary across three different axes. This stands in contrast to the more typical oblate spheroid shapes of other planets like Earth. The causes of this triaxiality have remained unclear for years. The hypothesis surrounding Nerio suggests that Mars's early molten state and the gravitational pull of a large moon may have permanently deformed its surface.

As Mars cooled, this gravitational interaction could have led to the formation of significant surface bulges. A prominent example is the Tharsis bulge, a massive highland area near the equator that spans around 5,000 kilometers. This region is home to towering volcanoes, including Olympus Mons, the tallest mountain in the solar system. Nearly opposite Tharsis, another highland exists, suggesting that these two regions may have been shaped by similar forces. Efroimsky’s theory posits that these formations were a direct consequence of Nerio’s gravitational influence, locking these features into place as the planet solidified.

Nerio’s Influence on Mars’s Volcanic and Tectonic Activity

Mars's terrain is notable not just for its large bulges but also for its extensive volcanic activity, which has shaped much of the planet’s surface. The presence of Olympus Mons and other massive shield volcanoes in the Tharsis region is evidence of volcanic processes that were likely influenced by the planet's unusual shape. Efroimsky’s hypothesis goes further, suggesting that Nerio’s gravitational pull may have enhanced volcanic activity on Mars. As the moon orbited in synchrony with the planet, it would have created a constant gravitational stress on the surface, encouraging magma flow and the formation of volcanic features.

These interactions may also explain the presence of Mars's highlands, especially the formations directly opposite Tharsis, such as Terra Sabaea. In the early history of Mars, when the planet's crust was still forming, Nerio’s gravitational pull could have caused magma and tectonic activity to concentrate in specific areas, reinforcing the development of these highlands.

The Fate of the Lost Moon

While the theory of a massive moon influencing Mars is compelling, it also raises questions about what ultimately happened to Nerio. Efroimsky speculates that the moon may have met one of two fates: it was either ejected from Mars's orbit by a gravitational encounter with another celestial body or destroyed in a massive collision, possibly with an asteroid or another planetesimal. If destroyed, the debris could have led to the formation of Mars's two current moons, Phobos and Deimos, which are much smaller in size.

However, the lack of direct evidence for Nerio's existence, such as crater patterns or remaining orbital debris, makes this part of the hypothesis challenging to confirm. If a large impact destroyed the moon, it might have left behind a distinct chain of craters aligning with the moon’s former orbit, but no such features have been definitively identified. Nevertheless, the idea that such impacts were common during the chaotic early days of the solar system lends some credibility to the hypothesis.

Looking Ahead: Verifying the Hypothesis

As with any scientific hypothesis, more research is needed to confirm or refute the idea that a lost moon shaped Mars. If Efroimsky’s theory holds up under further scrutiny, it could profoundly alter our understanding of Mars’s geological history. For now, scientists must rely on geological surveys and computer simulations to explore how a moon of Nerio’s size could have affected Mars over time.

While the direct evidence of Nerio may be elusive, the proposal opens up exciting possibilities for understanding the formation of not just Mars, but other planets as well. Similar processes may have occurred elsewhere in the solar system, leading to the formation of moons and shaping planetary features in ways not yet fully understood. Continued exploration, including missions to Mars’s moons and further study of its geological record, may one day reveal the truth behind Mars's mysterious shape.