Amalthea
The Red Potato
Jupiter's fastest major moon, orbiting in just 12 hours, covered in red sulfur from Io
🌙 Mind-Blowing Fact
Amalthea completes an orbit in less than 12 hours - you could watch it rise and set TWICE in one Earth day!
What is Time on Amalthea?
What is Time on Amalthea?
Amalthea is Jupiter's closest major moon, racing around the giant planet in less than 12 hours. It's a small, potato-shaped moon covered in reddish material from its neighbor Io's volcanoes.
The 12-Hour Orbit
- One orbit = 11.95 hours - Less than an Earth half-day!
- Jupiter fills the sky - 46 degrees across (92 full moons!)
- Tidally locked - Same face always toward Jupiter
- You'd see Jupiter rotate 2x per orbit - Watch the Great Red Spot pass twice!
The Fastest Major Moon
Amalthea is the fastest significant moon in the Jupiter system:
- Orbits 2x per Earth day
- Jupiter rotates 2.4x per Amalthea orbit
- Io (next moon out) takes 1.77 days
- Result: You could watch Io slowly creep across Jupiter's face
Red from Sulfur
Amalthea's distinctive red color comes from:
- Sulfur particles ejected by Io's volcanoes
- Swept up as Amalthea orbits through Jupiter's magnetosphere
- Creates a unique reddish hue unlike any other moon
A Day in the Life
The Fast Lane
You stand on Amalthea's surface, watching Jupiter dominate 46 degrees of sky. It's been 6 hours since you landed, and Jupiter has rotated completely once. The Great Red Spot is coming around for its second appearance.
"Sunrise in 30 minutes," your companion says. The sun will rise in the exact same spot it set 5.97 hours ago.
On Amalthea, time moves FAST. Two orbits per Earth day. Jupiter spinning visibly in the sky. This is the express lane of moons.
Thought Experiments
How would you tell time on Amalthea?
You could use Jupiter's rotation! Watch the Great Red Spot - it passes by twice per Amalthea orbit. Count Red Spot transits to measure time. Or watch Io rise over Jupiter's limb - it takes multiple Amalthea orbits for Io to complete one revolution.
The Science of Time on Amalthea
The Science of Amalthea
Amalthea is Jupiter's fifth moon (J5) and the reddest object in the solar system. Its rapid 12-hour orbit and reddish sulfur coating make it unique among major moons.