Feminine of hesperian ("relating to citrus fruits or geographical regions known as Hesperia").
It means Hesperia. Relative to Hesperia (Hesperos, meaning western land). Belonging to or relating to the Iberian or Italic peninsulas. As for the Geology of Mars it is the name of the second geological era, between the Noachian and the Amazonian.
2 . In the study of the geology of Mars, it is the second era, between the Noachian and the Amazonian. It is estimated to have lasted between 3.5 and 1.8 billion years. The main feature is the formation of extensive lava plains.