I've read that manned exploration of asteroids such as Vesta would be difficult due to the scanty gravity they possess. If their gravity is so weak, I have a few questions:

1) How can a spacecraft achieve a stable orbit around one if the gravity is so weak that an astronaut could jump into orbit from a standing position on one?

2) Why do the spacecraft orbit so FAR away (for example, 1700 miles) instead of coming in really close, seeing as how the weak gravity would not cause the craft to fall into or crash into the asteroid?

Astronut out there, any ideas?