An interesting space game
As an asteroid, you need to collide with other asteroids in order to grow and then you become a planet.
As a planet, you need to get close to asteroids so your gravitational pull drags them into your orbit. Once that happens you can absorb them to gain mass. Eventually you will become a Life Planet.
As a Life Planet, military forces appear, but you do not control them. Ships will spawn from your planet, guns will appear, and you have a rechargeable shield. Absorbing asteroids will turn you into a Star.
As a Star, you will need to get close to planets so your gravitational pull drags them into your orbit. You can then absorb these to gain mass. You can still increase the mass of your planets by using the same technique, and then absorb these into your star to gain mass quicker.
Eventually, you will form a black hole which sucks everything into it. The only danger is other black holes which you must avoid.
You need to be quite careful navigating near planets and asteroids, because your gravitational pull can drag them straight into you which damages you and reduces your mass. The technique is to get close but to keep moving so they just lock in place.
There are a variety of missions with all sorts of objectives, from protecting planets, destroying planets or systems, stealing planets, destroying alien ships. A lot of the missions are difficult and the game doesn't give you much hints. It's important to keep your mass topped up, and use asteroids as extra shields before charging in to ram other system's planets. You must navigate carefully because you need to avoid other star's gravitational pull, which can drag you to your demise. You can go into the menu and tinker with the physics to change the gravity and damage if you wish in order to make the game easier or behave differently.
Solar 2 is an interesting game and can be played at your own pace. The missions provide a challenging experience, but outside the missions it is more of a casual affair. Despite it being interesting, I just didn't find it that fun and didn't think it provided more than a few hours of entertainment.