What's that in Io's sky? (Destiny)

by Cody Miller , Music of the Spheres - Never Forgot, Tuesday, August 07, 2018, 22:46 (2376 days ago)

So the other day I was on Io. Waiting for that Whisper of the Worm event. Up in the sky there was a perfectly round moon between Io and jupiter.

What is it? Only 4 moons are closer to Jupiter than Io, and none of them are round, nor big enough to appear like that in the sky.

What's the story?