Cassius (named after a conspirator in the play Julius Caesar written by William Shakespeare) is a greenish-blue planet orbiting the star Proxima Centauri, about 4.2 light-years from earth. It is a terrestrial (not gaseous) planet with an atmosphere comprised mostly of carbon dioxide and Nitrogen. Cassius has several rings around it made up of rocks and ice.
Cassius' moon Brutus is one fourth the size of the planet. Its reddish color is due to the high iron content in its rocks and soil. Brutus has no atmosphere.
Cassius Prime, the first colony on Cassius was established in 2149 by mining entrepreneur Aric Schröder when he set up Cassius Mining Company, headquartered on Brutus.