system
Given the following post, respond as if you're commenting on Reddit:
human
Why is water so hard to find on other planets when it is such a simple compound?
gpt
The other answers here are wrong. Water can be found on literally all the planets in our solar system, just not necessarily in liquid form:

- Mercury: Mostly too hot for water to exist without boiling/evaporating off the planet, but very substantial amounts of water ice exist deep in the permanently shadowed regions of craters at the poles.

- Venus: Definitely used to have lots of water (perhaps even oceans), but most of it dissociated high in the atmosphere and the hydrogen escaped as individual atoms, while the oxygen was likely locked up in CO2. Now only tiny trace remnants of water vapor exist in the atmosphere.

- Earth: Obviously tons of water vapor, liquid water, and ice. Quite a bit of water is locked up as hydrated minerals in the crust/mantle, as well.

- Mars: Lots of water ice just under the surface, especially at the poles. Liquid water may exist briefly, or perhaps for sustained periods deeper down in the crust where the pressure is sufficient.

- Jupiter: Huge amounts of water ice at the core, and the lowest layer of clouds are made of liquid water droplets that produce rain frequently. 

- Saturn: Like Jupiter, lots of ice at the core, and a lower cloud deck made of water.

- Uranus: Beneath most of the atmosphere, vast oceans of slushy superionic water mixed with ammonia. Probably lots of water ice at the core, too.

- Neptune: Like Uranus, oceans of superionic water and ammonia. Also lots of ice at the core.

As for moons, most of them have water in some phase:

- Liquid water: Europa and Enceladus both have a substantial amount of liquid water under the ice shell.

- Water ice: Almost all the outer moons have lots of ice - Ganymede, Callisto, Titan, Rhea, Iapetus, Dione, Tethys, Mimas, Hyperion, Titania, Oberon, Ariel, Umbriel, Miranda, Puck, Triton, Nereid, etc. There's evidence suggesting that our own Moon also has ice in the permanently shadowed craters at the poles.

For smaller bodies, Ceres, Pluto, Makemake, Eris, Haumea, Quaoar, etc. all have vast amounts water ice.