Metaphasic radiation, concentrated in the rings of the Ba'ku homeworld, continually regenerates living cells and grants those who live there a greatly extended life.
The Ba'ku settled their planet centuries before the 2370s and found that radiation from its rings kept them healthy and youthful. Because the particles are constantly renewed in the rings, residents age extraordinarily slowly, and visitors who stay soon feel their own bodies revitalized.
The Son'a, estranged descendants of the Ba'ku, wanted to collect the radiation using a process that would leave the planet uninhabitable. In 2375 a Starfleet admiral cooperated with them in a plan to relocate the Ba'ku in secret, but Picard and the Enterprise-E crew refused to take part and exposed the scheme.