Mercury has no atmosphere, just an exosphere. The highest mountain range on Mercury are the Caloris Montes, reaching up to 1.9 miles (3 km). What if a spacecraft tried to orbit Mercury at an altitude of 3 miles (4.8 km)? Since Mercury has no considerable atmosphere, would the spacecraft have a stable orbit? If no, why not? A similar question could be asked on the Moon which however wouldn't be a good example due to the extreme mascons of the Moon. Such a question could however work with Ceres and any other spherical celestial body without a considerable atmosphere too probably.