Can New Horizons probe turn back and start orbiting Pluto
A Pluto orbiter would have been possible, but then the entire mission would have to be designed around that. New Horizons was designed as a small fast probe that could reach Pluto relatively quickly (almost 10 years), but not be able to stop there. An orbiter would have to take a lot more fuel with it, and approach Pluto slower. Such a mission would therefore take a lot longer to reach Pluto, i.e. it could easily take double the time or more, and would be more expensive.