From Halopedia, the Halo wiki
During the Fall of Reach in 2552, Tantalus hosted a small number of warships in orbit. These vessels were called upon by Admiral Roland Freemont to aid in the defense of Reach. Like all other human colonies in the Epsilon Eridani system, Tantalus was attacked during the Covenant's invasion of the system.
Government and society
In the 2001 version of Halo: The Fall of Reach, Admiral Roland Freemont requests all UNSC ships from the Epsilon Eridani, Tantalus, and Jericho systems to aid in the defense of Reach. However, the 2011 Definitive Edition removes the latter references, likely because the so-called "Jericho system" had been compromised in 2535, while the Halo Encyclopedia: The Definitive Guide to the Halo Universe had previously established Tantalus to be a planet in the same system as Reach.
The planet was named for a figure from Greek mythology.
List of appearances