At the end of the movie Gravity, Sandra Bullock's character manages to pilot and crash a module into an ocean, surviving the impact and making it to the planet surface. Oli's original question is: which planet is she landing on? The answer is definitely the Earth, for two reasons.
Firstly, the rest of the film takes place in orbit around Earth and to crash onto another planet would be too enormous a distance to travel. The distance between the International Space Station and Earth, compared to the distance to the International Space Station and Mars (the nearest planet) is like the distance between your left eye and your right eye, compared to the distance between your left eye and Antarctica.
The second reason we can decide it's Earth is that there are lots of plants around. At the moment, Earth is the only known planet in our solar system to have plants. If she'd landed on Mars it would have looked like a rough, reddish brown desert. Not a fun place to be. So the answer is definitely: she's crash-landing on Earth.