According to Guinness World Records,The McMurdo Dry Valleys are the coldest dessert.

Located in Antarctica, with an area of 4,800 square kilometers the McMurdo Dry Valleys have average annual temperature of -20ºC (i.e. -4ºF). The reason it is called dry valleys is because of its extremely low humidity. The harsh environment of Dry Valleys is considered to be very similar to the Mars by the scientists. Since life (e.g. bacteria) is found in Dry Valleys despite its inhospitable conditions, there might be life on the Mars as well.