http://www.space.com/21364-moon-gravity-mascons-mystery.html writes to say
...These geologic structures, called mascons (short for mass concentrations), are so dense they alter the moon's gravity field, causing perturbations that can tug a spacecraft lower in its orbit around the moon, or push it wildly off course...
Lacking an atmosphere, perhaps Luna exhibits the acute form of this malaise. If a celestial body -
- lacks an atmosphere,
- has a superficial/non-existent magnetosphere, and
- has a near solid core
would it follow that it would have lumpy gravity?
What celestial bodies are known to be lumpy in gravity?