Mars, often referred to as the Red Planet, is one of the most fascinating celestial bodies in our solar system. Among many of its intriguing features, Mars has two small moons that have captured the interest of astronomers and space enthusiasts worldwide.
These moons, though tiny compared to Earth’s Moon, play significant roles in our understanding of Mars and the dynamics of planetary satellites.
In this article, we will explore exactly how many moons Mars has, their individual characteristics, the history behind their discovery, and what makes these moons unique in the solar system.
Number of Moons Mars Has
Mars has two natural satellites. Unlike the Earth, which has one large moon, Mars’ moons are small and irregularly shaped.
These moons are named Phobos and Deimos.
Their small size and proximity to Mars make them quite different from the large, spherical moons orbiting the gas giants like Jupiter and Saturn. Phobos and Deimos are believed to be captured asteroids or remnants from the early solar system.
“The two moons of Mars are among the smallest moons in the solar system, yet their discovery has provided invaluable insight into planetary formation and the history of Mars.”
The Moons of Mars: Names and Origins
Phobos and Deimos are named after the Greek mythological figures associated with the god of war, Ares (the Greek counterpart to the Roman god Mars). Phobos means “fear” and Deimos means “terror” or “dread.” These names were chosen to reflect the ominous nature of war, fitting for Mars, the god of war.
Both moons were discovered in 1877 by American astronomer Asaph Hall at the United States Naval Observatory. Their discovery was a landmark moment in astronomy, providing direct evidence that Mars, like Earth, has natural satellites.
Phobos
Phobos is the larger and innermost moon of Mars. It orbits very close to the planet—so close that it completes an orbit in just about 7.6 hours, which is faster than Mars’ rotation period.
This means Phobos rises in the west and sets in the east, an unusual behavior for a moon.
With a mean diameter of approximately 22.4 kilometers (about 14 miles), Phobos is tiny compared to Earth’s Moon, but its proximity to Mars makes it an intriguing object of study. Its surface is covered with craters and grooves, and it is gradually spiraling inward toward Mars, which will eventually lead to its destruction or possible formation of a ring around the planet in tens of millions of years.
Deimos
Deimos is smaller and more distant from Mars than Phobos. It has a mean diameter of about 12.4 kilometers (roughly 7.7 miles), making it about half the size of Phobos.
Deimos orbits Mars every 30.3 hours, which means it moves more slowly in the sky compared to Phobos.
Deimos’ surface is smoother than Phobos’ because it is covered with a thick layer of regolith (dust and debris), which fills in many of its craters. Its far orbit keeps it relatively stable, and unlike Phobos, it is slowly moving away from Mars.
Comparison of Mars’ Moons
| Feature | Phobos | Deimos |
|---|---|---|
| Mean Diameter | 22.4 km (14 mi) | 12.4 km (7.7 mi) |
| Orbital Distance from Mars | 9,376 km (5,827 mi) | 23,460 km (14,580 mi) |
| Orbital Period | 7.6 hours | 30.3 hours |
| Surface Features | Craters, grooves, regolith | Cratered, covered with thick regolith |
| Orbital Direction | Prograde (same direction as Mars rotation) | Prograde |
| Discovery Year | 1877 | 1877 |
Scientific Importance of Mars’ Moons
Phobos and Deimos offer scientists a unique opportunity to study the processes that govern small bodies in the solar system. Their irregular shapes, compositions, and orbits suggest an origin different from many other moons, potentially captured asteroids from the nearby asteroid belt.
Studying these moons can provide clues about the early solar system and the processes that shaped Mars. Phobos, in particular, is a candidate for future missions aimed at sample return, which could offer direct evidence about the moon’s material and origin.
Potential for Human Exploration
Phobos has been proposed as a potential base for human missions to Mars. Its low gravity makes landing and takeoff easier compared to Mars itself.
It could serve as a staging ground for Mars surface exploration or as a platform for scientific observations.
Deimos, while more distant, also presents possibilities for robotic and human exploration. Both moons’ proximity to Mars allows them to serve as stepping stones for extended Mars exploration.
Historical Context and Discovery
The discovery of Phobos and Deimos was made possible by advancements in telescope technology in the 19th century. Asaph Hall, working at the U.S.
Naval Observatory, used a 26-inch refracting telescope, one of the largest of its time.
Hall’s discovery was met with excitement because it confirmed predictions that Mars might have satellites. Prior to this, moons around other planets had been discovered (such as Jupiter’s four Galilean moons), but Mars had remained elusive.
The names Phobos and Deimos were suggested by Hall’s wife, who was familiar with Greek mythology. The names have since become standard, symbolizing the connection between Mars and the mythology of war.
Physical Characteristics of Phobos and Deimos
Phobos and Deimos are both irregularly shaped and much smaller than Earth’s Moon. Their surfaces are heavily cratered, but Phobos shows additional linear grooves and ridges that are still not fully understood.
Phobos’ most famous feature is the large crater called Stickney, which is about 9 kilometers in diameter—almost half the moon’s width. The impact that created Stickney likely shaped much of Phobos’ current surface.
Deimos, on the other hand, appears smoother due to its thick layer of regolith that covers many of its craters. This regolith helps protect the underlying rock from micrometeorite impacts and space weathering.
Orbital Dynamics
The orbits of Phobos and Deimos are unusual compared to many moons in the solar system. Phobos orbits very close to Mars, so close that it completes more than three orbits for every rotation of Mars.
This rapid orbit causes tidal interactions that are gradually lowering Phobos’ altitude.
As a result, Phobos is slowly spiraling inward and is predicted to either crash into Mars or break apart to form a ring around the planet in about 30 to 50 million years.
Deimos, meanwhile, orbits farther away and is slowly drifting outward due to tidal forces, making its orbit more stable over long periods.
Exploration Missions to Mars’ Moons
Several space missions have studied Phobos and Deimos, both from orbit and via flybys. The Mars Global Surveyor and Mars Express have provided detailed images and data about these moons.
Japan’s Martian Moons eXploration (MMX) mission, scheduled for the mid-2020s, aims to land on Phobos, collect samples, and return them to Earth. This mission is expected to revolutionize our understanding of the moons’ composition and origin.
Summary
Mars has two moons: Phobos and Deimos. These small, irregularly shaped satellites orbit close to the Red Planet and provide important insights into planetary science.
Both were discovered in 1877 and named after mythological figures symbolizing fear and terror.
Phobos is larger and closer to Mars, with an orbit so rapid that it rises in the west. Deimos is smaller and more distant, with a smoother surface.
The moons’ origins are still debated, but studying them helps scientists understand Mars’ history and the broader solar system.
Future missions, such as Japan’s MMX, will deepen our knowledge and may even pave the way for human exploration starting from these fascinating Martian moons.
