Tarella

From Memory Alpha, the free Star Trek reference

Tarella was an M-class planet and the homeworld of the Tarellians. It was very similar to Earth.

A civil war between the planet's two main continents led to the destruction of the Tarellian civilization after biological weapons were deployed. A few Tarellians managed to escape the planet in ships. (TNG: "Haven")

According to the script of the episode, Tarella was the second of six planets in its star system.