UNSC Tharsis (Reach)

The UNSC Tharsis was a UNSC vessel of the destroyer class. In August 2552, the Tharsis was stationed near Reach. When 314 Covenant vessels attacked the system, the Tharsis was involved in the ensuing battle, where it was heavily damaged.

Three weeks later, the Covenant had towed the Tharsis to a "graveyard" over the northern pole of Reach, with the rest of the hulks of ruined starships from the battle. The Tharsis was damaged but not destroyed, and it still had an intact fusion reactor. When Cortana and the Master Chief returned to Reach aboard the Ascendant Justice, Cortana looked in the graveyard for a ship to fuse the Ascendant Justice with, as its own reactor was damaged. She narrowed the search down to the Tharsis and the UNSC Gettysburg, but selected the Gettysburg over the Tharsis because the former ship had less damage and an intact MAC gun.

Historical Reference
The Tharsis region on Mars is an enormous volcanic upland located on Mars' equator, at the western end of Valles Marineris. Its name comes from the bible, where it was the name for the land at western extremity of the known world