Ok, can we just talk for a second about how this lil moon of Neptune's bounces up and down like a carousel horse to avoid collisions with the moon Thalassa?

Orbital dynamics are FASCINATING.

Let's break down what's happening here. (1/n)

: @NASA / @NASAJPL

Naiad is the innermost moon of Neptune, discovered in 1989 in Voyager 2 images. It's irregularly shaped & is teeny-tiny, at less than 100km at its longest.

Naiad orbits Neptune in just *7 hours!*

(This image is a perfect example of why we need an outer solar system mission)

Thalassas is the next innermost moon & orbits Neptune in 7.5 hours. Its orbital radius is only 1850km larger than Naiad's, which is a tiny difference on solar system scales!

If all other things were equal, the two moons would get uncomfortably close.

Enter orbital resonance!

Resonances happen when the period ratios of two objects are integers. They either stabilize the orbit (like with Pluto and Neptune) or destabilize the orbit (like with Jupiter and some families of asteroids).

Naiad orbits 73 times for every 69 of Thalassas'.

Naiad's orbit is also inclined by 5º relative to Thalassas'. This helps increase the distance btwn the two moons at closest approach to almost 4000km.

Compare to less than 2000km if they were in the same plane.

So Naiad's dance helps keep both moons in stable orbit!