If you say water
then we say volcanism,
else Mars is too cold.
Recent observations of Mars have suggested the presence of liquid water beneath the ice at the South Pole, prompting researchers to ask how water could exist in liquid state under Mars’ environmental conditions.
Research by Soria and Bramson (2019) suggests that the most likely theory to explain the presence of water would be an underground source of heat such as the formation of a magma chamber in the area within the past few hundred thousand years. The researchers also suggest the reverse is true – if there isn’t such a heat source then it’s unlikely that the earlier suggestions of liquid water are correct.
Original reseach: http://dx.doi.org/10.1029/2018GL080985