Mercury
noun, の adjective
The water star is the planet Mercury. That's where we hid all of our secret moon water. Mercury looks enough like our moon, so we put it there so no one could find it.
すいせい
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
水星には大気がありません。
Mercury does not have an atmosphere.
こんなはずじゃなかったんですが、もう十年も水星でホームレスをしています。
This isn't what I asked for, but I've been homeless for 10 years on Mercury.
水星は、日の出直前、または日没直後しか見ることができない。
I can only see Mercury just before sunrise and right after sunset.