Earth
From Halopedia, the Halo wiki
Summary
Earth is the homeworld of the human race. It is the UNSC's last bastion of power, since Reach fell, and is heavily protected with Super MAC orbital platforms, over a hundred heavy cruisers, and many other experimental defense systems. The UNSC have taken no chances with keeping the secret of Earth safe, though it was only a matter of time before the Covenant discovered Earth's location.
The Attack
In 2552, Earth came under attack by the Prophet of Regret's fleet. It is likely that Regret came in search of a Forerunner installation (probably The Ark), possibly from directions from the Forerunner installation on Coral. Regret had never intended to face such a strong human force, and went after the installation himself while his fleet engaged the humans in orbit.
