This is a story/novel I read a long time ago. I read it around 10-15 years ago, but I believe it was released much earlier than when I read it. The book was quite thick, as thick as or thicker than Harry Potter: the Half Blood Prince or The Order Of the Phoenix. I'll try my best to remember some of the story:
- The boy's parents live in a space station on the moon. I think his father's job is a mechanic or something to do with spacecrafts.
- The boy found some crystal/mechanical device after a comet/asteroid/UFO passed by.
- The thing that the boy found opened some kind of a gate that sucked the boy through.
- When the boy came out of the gate, he came out of a structure/building; the gate was opened inside the building.
- The boy visited various planets using the gate and tried to get back home.
- In the middle of the story, a girl (alien but human-like?) joined the boy in travel through the gate.
- I think in the end the boy succeed to get back home with the girl. but time has long passed
That's all what I remember about the book, I do not really remember much more because back than I was not paying attention except for the story. I think the background cover is a boy seen in outer space.