Thank you for the feedback! We'll need to incorporate some more info inside the game for sure, for the jam we decided to explain everything on itch's project page (first game jam, we didn't know it's possible to download a game straight from the submission page, whoops...)
The goal is to reach the black hole before the timer runs out and the bomb explodes. Going through a planet gives you perminant speed boost, so the more planets you go through, the faster you go. There's no way to reach the end without going through the planets, the rocket is just too slow :)