PGravity
You can use this Node to exert a force on particles similar to that of gravity or of a magnet. The mass and the size of the particles can be taken into account.
We are simulating real gravity here by changing the strength of the gravity as the particle stream gets close to a Gravity object. So you could, for example, deflect small meteorites around a heavy planet. Use the RangeMapper node to adjust how the distance affects the gravity strength.