Hydra

Hydra is the outermost of Pluto's five moons and carries a bit of a "mysterious" reputation compared to the well-studied Charon. It was discovered in 2005 by the Hubble Space Telescope team, alongside its sibling moon, Nix.

1. The "Water Moon"

Hydra is named after the nine-headed serpent from Greek mythology that guarded the entrance to the underworld. The name is also a clever nod to the "H" in Hubble (the telescope that found it).

• Composition: Data from the New Horizons mission revealed that Hydra’s surface is covered in almost pure water ice.

• Reflectivity: Because of all that ice, Hydra is incredibly reflective—it's much brighter than you’d expect for such a small rock.

2. Chaotic Rotation (The Tumble)

Most moons in our solar system (like our own Moon) are "tidally locked," meaning they always show the same face to their planet. Hydra is different:

• It spins rapidly and chaotically.

• Instead of a smooth orbit, it "tumbles" through space like a football.

• This is caused by the shifting gravitational pull of the Pluto-Charon "double planet" system, which prevents Hydra from settling into a steady rhythm.

3. A Strange Shape

Hydra isn't a perfect sphere; it looks more like a lumpy potato or a jagged comet nucleus.

• Dimensions: It measures roughly 55 km by 40 km (34 miles by 25 miles).

• Impacts: Its surface is heavily cratered. Scientists have noted at least two large craters, one of which shows a darker interior, suggesting Hydra might have different materials hidden under its icy crust.

Characteristics:

• Distance from Pluto - ~64,700 km (The furthest out) 

• Orbit Time - About 38 Earth days 

• Size - Small (roughly the size of Rhode Island) 

• Discovery - 2005