Sure! Here's a simple example of a 3D Solar System game implemented in a single HTML file using JavaScript and enclosed in script tags. Please note that this example is simplified for brevity and doesn't include complex physics or realistic planet movements. It will allow the player to move the planets and stars using smartphone operation:
In this game, you'll see a star at the center of the screen. You can touch or move your mouse across the screen, and the player (represented by the star) will follow. There are also planets orbiting around the star. The planets' positions are updated based on their distance, speed, and angle. Feel free to enhance this game further by adding interactivity or additional features as per your requirements and design preferences.