The Mercurians have discovered the secret of near perfect energy storage. Their proximity to Sol allows them to charge their standard batteries for nearly free. This energy supply and demand has made their nation wealthy beyond imagination. Their Power Point, a standard battery that is used in all walks of life, from spaceships to buildings, can easily power an entire office building for a year before recharge.
There are nobles and there are servants. There is no in between natively from Mercury.
The High Nobles are the lackadaisical kings and queens of their realm living in luxury and excess.
Lower nobles (grandchildren, cousins, etc) are known to handle the properties of the Sun Kings and are quite adept at the repair and maintenence of the solar arrays owned by their family. These nobles are the equivalient of the working middle class which is still very wealthy by the standards of the rest of the system. All nobles, both high and low and all in between are pure Mercurian stock humans.
The commoners handle all the other menial tasks that are not directly related to the maintenence and recharging of power points. They are treated no better than robots or slaves by the higher nobility. The lower nobility's attitudes and treatment of the Commoners depends from person to person, some treat them as scum, some treat them as equals, but as a general the lower nobility treats the Commoners as a commodity not "real" people. They are wage slaves scraping up the drippings left behind by the indulgence of the nobility.