Keetol was the site of a major battle in the Last Great Time War. The Daleks wanted to mine the planet for its weapons-grade rocks. The Master helped the Time Lords achieve a victory, one of their first in the War.
After the Master changed history using the Heavenly Paradigm, the Daleks won the battle. The rings around the planet were formed by destroyed Time Lord vessels. As a result of the TARDIS engine debris, passing through Keetol's rings caused localised temporal shift. (AUDIO: The Heavenly Paradigm)