and that white glistening stuff there, that is icelandic cave bacteria. it doesn't need any light to live. it can survive in near—freezing temperature. it just feeds off the iron and the sulphur in the rocks down here, away from everything else. so what we think is that if there are lava tubes on mars, there could be life in there, too. next, daniel is keen to show me another terrestrial analogue a couple of hours' drive from the lava tube, and this one is even more extreme. we're going under the ice to an environment of very different challenges. we think about the lava tube that we visited earlier — that's a ready—made structure perfect for potential habitat. whereas the analogue we're