Moons of Mars

Discovering Mars’ Tiny Twins: Phobos and Deimos

Imagine two tiny moons orbiting the Red Planet—Phobos and Deimos. These diminutive companions, discovered in 1877 by American astronomer Asaph Hall, are more than just celestial curiosities; they hold secrets about Mars’ past and future.

Origins of Mystery

How did Phobos and Deimos come to be? Two hypotheses dominate the scientific discourse. One suggests that these moons formed from a giant impact event on Mars, while another proposes they are captured asteroids. The truth may lie somewhere in between, waiting for further study through sample return missions.

Historical Speculations

The idea of Martian moons has fascinated thinkers since the 17th century. Galileo Galilei observed Saturn’s rings and speculated about Mars’ ‘furious twins,’ while Johannes Kepler and Jonathan Swift furthered these ideas in their writings. Asaph Hall, driven by curiosity, discovered Phobos on August 12, 1877, and Deimos three days later.

Names and Notions

The names ‘Phobos’ (fear) and ‘Deimos’ (terror), suggested by Henry Madan from Homer’s Iliad, add a layer of myth to these moons. The story goes that Phobos and Deimos accompanied the god Ares into battle, much like their celestial counterparts circle Mars.

Mars Moon Hoax: Fact or Fiction?

In 1959, Walter Scott Houston claimed ‘Dr. Arthur Hayall’ said Mars’ moons were artificial satellites in his column for the Great Plains Observer. Soviet scientist Iosif Shklovsky repeated this claim based on a density estimate that was later disproven. Recent surveys by Scott S. Sheppard and David C. Jewitt in 2003 failed to find additional moons, debunking the hoax.

Observations and Characteristics

From Mars’ surface, Phobos would appear about one-third as big as a full moon near its equator, shrinking further at higher latitudes. Deimos, on the other hand, appears like a bright star or planet with an angular diameter of about 2′. Phobos rises and sets quickly due to its close orbit, while Deimos rises slowly in an outside synchronous orbit.

Motions and Tides

Phobos rises in the west, sets in the east, and rises again in eleven hours. Deimos rises in the east but very slowly. Both moons are tidally locked, presenting the same face towards Mars. Phobos’s orbital radius is decreasing due to tidal forces, potentially leading to break-up or collision with Mars. Deimos, being farther away, is being slowly boosted into its orbit.

Future Missions and Exploration

The origin of Martian moons remains a mystery. Both are thought to be captured main-belt asteroids, but this hypothesis has limitations due to their circular orbits and lack of evidence for capture through atmospheric braking. Alternative hypotheses include the coalescence of second-generation Solar System objects, a collision with a large planetesimal, or a massive impact on Mars followed by gravitational interactions.

These hypotheses are supported by observations of Phobos’ composition, which is distinct from asteroidal material, and the fine-grained surface of both moons. This would create a disc around the planet with large amounts of water that cooled it down and changed the chemical composition of the rocks, likely producing phyllosilicates.

Past attempts and proposals for missions to Phobos and Deimos included probes launched in 1988, a failed sample return mission from Phobos, and several other concepts proposed by NASA, the European Space Agency, and Canadian Space Agency. Current proposals include the Martian Moons eXploration (MMX) mission, which aims to launch in 2026 and bring back samples from Phobos, as well as a sample return mission concept for Deimos called Gulliver.

As we continue to explore these enigmatic moons, the mysteries they hold will undoubtedly shape our understanding of Mars and its history. The journey to uncover their secrets is just beginning, and every discovery brings us closer to unraveling the cosmic tapestry that surrounds our Red Planet.