Astronomy 92 - Mars - Part 4 - Martian Moons

Overview

This lecture discusses Mars' two small moons, Phobos and Deimos, focusing on their origins, physical characteristics, orbital behavior, mythological names, and hazards of exploration.

Mars’ Moons: Phobos and Deimos

• Mars has two moons: Phobos and Deimos.
• Both moons are tiny, about 12 kilometers wide each, much smaller than Earth's moon.
• From Mars’ surface, the moons would appear as small dots, similar to stars.
• Phobos and Deimos resemble asteroids in shape and size.

Origin and Orbits

• The moons are likely captured asteroids from the asteroid belt.
• Their orbits are unstable compared to typical moons.
• Phobos’ orbit shrinks slightly with each revolution and will eventually crash into Mars in millions of years.
• Deimos’ orbit is slowly expanding and may eventually escape Mars’ gravity into space.

Impacts and Hazards

• The likely future impact of Phobos will be significant, as it is larger than the asteroid that killed the dinosaurs.
• Satellites should be kept distant from the impact to avoid destruction by heat, debris, or vaporization.
• Walking on either moon is extremely dangerous due to extremely low gravity; even a small stumble could fling a person into space.

Names and Mythology

• Phobos and Deimos are named after mythological Greek gods who served the God of War (Mars/Ares).
• Phobos is the god of fear (root of the English word "phobia").
• Deimos is the god of terror.

Key Terms & Definitions

• Asteroid Belt — Region in space between Mars and Jupiter with many small rocky bodies.
• Captured Asteroid — Asteroid that is caught by a planet’s gravity and becomes a moon.
• Orbit — The path an object takes as it moves around a planet or star.
• Gravity — The force attracting objects toward one another, weaker on small moons.

Action Items / Next Steps

• Review the characteristics and origins of Mars’ moons.
• Understand the dangers of low gravity on small celestial bodies.
• Familiarize with Greek mythology related to Mars’ moons.