Mars aka the Red Planet, continues to be a subject of discussion and curiosity among astronomers. Recent research presents a hypothesis that Mars may have once been home to a large moon, now long lost, that contributed to the planet’s topography.
This theory, proposed by US Naval Observatory astronomer Michael Efroimsky, suggests that this ancient moon, named Nerio, might unlock some of Mars’ features, including its uneven shape and the formation of its massive volcanoes.
Mars is not shaped like a perfect sphere. Due to its varying width, length, and height, the planet is categorized as triaxial. This unusual characteristic, along with striking topographical features like its towering peaks and deep valleys, presents a planetary mystery. According to Efroimsky, these features could serve as tangible evidence of a large moon that once orbited Mars but eventually disappeared.
Efroimsky’s recent, yet-to-be-peer-reviewed paper highlights the prominent Tharsis bulge, a massive feature near Mars’ equator that houses three of the largest volcanoes in the Solar System. While past studies have theorized that this bulge resulted from internal volcanic activity, some researchers have found that removing the Tharsis region from Mars would not alter its triaxial shape. This led Efroimsky to suspect that a moon, which he has named Nerio, may have influenced Mars’ early formation before it fully solidified.
Through his calculations, Efroimsky proposes that if Nerio existed and was at least a third of the size of Earth’s Moon, it could have exerted enough gravitational force on Mars to cause the formation of the Tharsis bulge and other distinctive features. As Mars cooled over time, this bulge would have become a permanent fixture on the planet’s surface.
However, the whereabouts of this mysterious moon remain unknown. Efroimsky speculates that Nerio may have been destroyed in a catastrophic collision, leaving behind only its remnants—Mars’ current moons, Phobos and Deimos, which are relatively small and irregularly shaped.
While this theory is intriguing, Efroimsky acknowledges that it is, for now, an “educated conjecture.” Proving this hypothesis will require more detailed Martian data. Several ongoing missions aim to uncover Mars’ secrets, from its lost atmosphere to potential hidden water. Japan’s Martian Moons eXploration mission, set to launch in 2026, could offer further insights.
This mission plans to study Phobos and Deimos closely and even collect samples from Phobos for analysis back on Earth. Such data could potentially answer some of the questions Efroimsky’s theory raises.
