One way to define the solar system is if bodies within it have a closed orbit around the Sun.
Is another star part of our solar system?We don't know of another star that is moving slowly enough to be in orbit with our Sun, so there must be a limit to the size of the solar system. What would happen to a planet placed halfway between the Sun and the nearest star? Would the planet fall towards the Sun or towards the other star? What if the planet was moving? Does it matter which direction the planet moves?
Try having several people hold a sheet stretched out smoothly. Now have two other people each grab a separate point well separated in the middle of the sheet and pull down to form two depressions in the sheet. Place or gently roll a marble along the hump between the two
depressions. The depressions represent the "gravity well" of each star's solar system. Try different amounts of tension on the sheet generally and on each of the depressions. Does this change in the "gravity" change the size of each "solar system"? How far away from one "star" can you roll the marble without it being captured by the
other "star"? Do you see a wall? Is a wall needed? What happens when you have more than two "stars"?
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