Melpomenia
The nineteenth Spacer World settled, mentioned in Foundation and Earth. It contained a large monument called the 'Hall of the Worlds', which contained a large room with the fifty Spacer Worlds listed with co-ordinates on a wall inscribed with a table containing seven rows and seven columns (with the last world, Solaria, appended to the bottom of the final column); Melpomenia was the origin point. Using data from these columns, translated by Janov Pelorat, Golan Trevize was able to construct a sphere, the centre of which would be roughly close to Earth. The planet itself, however, was rendered virtually uninhabitable by a radical climate change; the only life form able to survive it was a carbon-dioxide feeding 'moss'. Golan Trevize had to use his blaster to melt away the alien substance on his ship, and the face plates on his and Pelorat's space suits. Only after bathing the rest of the ship in the UV rays of the sun did he leave the forsaken planet. It is presumably named for Melpomene, the Muse of Tragedy.
Read more about this topic: List Of Foundation Universe Planets