But a ball needs to lose energy to not roll right back up a hill to the same height it came from. And if that "ball" is a mass from outside our solar system, it

But a ball needs to lose energy to not roll right back up a hill to the same height it came from. And if that "ball" is a mass from outside our solar system, it will roll right back out of the solar system just as easily as it rolled in unless there is enough forces to slow it down enough to capture it.