The lifeless sister planet to Thessia lacks water or oxygen. It is covered instead with deserts, the "air" a mix of carbon dioxide and ethane. The manageable temperatures and gravity on Piares led to heavy exploitation for mineral wealth in the beginning of the asari space age. Today, Piares is largely mined out.
Piares is named for an ancient asari goddess of death, who was not seen as a malefic figure, but as one who guided asari spirits on their final journey. From her home in the stars, she could grant an asari who had lost a lover the ability to restore them to life in another body. This legend, heavily modified, formed the basis for a recent, highly profitable human simstim called "Nekyia Corridor."
The Reapers targeted Piares from orbit, its population too small to bother harvesting. Wreckage of the old domed cities and spaceports dot the landscape.