Why is Mars's Moon Traveling the Wrong Way?

Azeem (azeemba.com)

Oct 12, 2024

View from the Curiosity rover on Mars.

  • Phobos, the closer moon, is rising from the west
  • Deimos, the farther moon, is rising from the east

Orbital Direction 🔄

Almost everything in the Solar System orbits in the same direction!

Why?

Known Retrograde Weirdos

Uranus

 

Known Retrograde Weirdos

Uranus

But Not Really!

Known Retrograde Weirdos

Venus

 

Known Retrograde Weirdos

Venus

But Not Really!

Known Retrograde Weirdos

Triton

Okay yea, weird.

Known Retrograde Weirdos

  • Uranus
  • Venus
  • Triton
  • ...And that's it!

ESA's orbiter Mars Express shows the two moons orbiting in the same direction!

Apparent Motion

Apparent Motion

Apparent Motion

  • Blue car: Rotation of Mars
  • Red Car: Phobos
  • Green Car: Deimos

Deimos: Like Our Moon

Phobos Rises Itself

Phobos Rises Itself

Like the International Space Station!

🔄

  • Deimos rises in the east because of Mars's rotation
  • Phobos rises in the west because of its own orbit
  • So Martian moons have all the possibilities covered?

Well, there is a third possibility!

Rise and Set in the East

Rise and Set in the East

Alas, no such configuration in the Solar System.

Except...Mercury

Except...Mercury

  • We have Mars beat
  • But Mars wasn't the real competition!

Questions?