|There is more information available on this subject at 51 Pegasi system on the English Wikipedia.|
The 51 Pegasi system is approximately 50.1 lightyears away from Earth, in the constellation Pegasus. The stars planetary system was controlled by the Covenant during 2545, and was home to 51 Pegasi B and Pegasi Delta, used by the Covenant in mining Deuterium and Tritium from the moon's rich oceans.
51 Pegasi was the very first main sequence (sun-like) star discovered to have a planet in orbit around it.
Pegasi Delta was also the home of an attack by the UNSC in 2545, in which 300 Spartan-III's from Beta Company were deployed from the UNSC All Under Heaven to destroy a Covenant refinery. The mission was a succes but only Tom-B292 and Lucy-B091 survived.