Old story about a boy who travels across the universe

Question

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.

Answer 1

Could be The Homeward Bounders by Dianna Wynn Jones. Link to wiki Points that fit:

• The cover does look like a boy on the moon.

• There are gates to enable the boy to move between worlds

• The boy is joined by a girl part way through

• The boy is trying to get home and succeeds but 100 years have passed and he can never get home.

Points that don’t fit:

• The boy lives in a village at the beginning.

• It’s not crystals that start his journey between worlds, it’s scheming god-like creatures. They force the boy to keep moving from world to world.

• It’s a thick book by Diana Wynn Jones standards, but not as thick as OOTP. Maybe 300 pages.

• No UFO.