Ashtallah

Ashtallah was a planet that was the home of the Ashtallan race.

Profile
Ashtallah had "rolling green hills, blue sky" like Earth but was much smaller than the human homeworld, despite having some similarities in its atmosphere and appearance. A large mountain range existed on the planet, bordering the valley of the Ashtallans. According to the First Doctor, it was on the other side of the galaxy from Earth. (AUDIO: The Invention of Death)

History
After the First Doctor, Susan, Barbara and Ian had left the Great White Hurricane in 1888, the Doctor attempted to use a temporal slingshot to return to 1963 London only for seventeen separate system failures to instead throw his TARDIS off-course and onto Ashtallah.

After the four had met the Ashtallans and discovered their immortality, the Ashtallans began dying off. It was soon discovered that Sharlan was the cause, using a sample of Barbara's blood, taken after she'd been injured, to kill her people in the hopes that a shorter lifespan might increase innovation. After Sharlan fell to her own plague and a vaccine had been developed for the rest of the Ashtallans, the TARDIS crew left the planet, pondering the impact that they'd had on Ashtallah. (AUDIO: The Invention of Death)