Is there life on Mars?

AROUND 3.5BN years ago conditions on Earth and Mars were similar. Both had thick atmospheres and liquid water on their surfaces. Both, in other words, had the conditions required to sustain life. And on one of those planets life was, indeed, sustained. Precisely when biology began on Earth remains obscure. But by 3.5bn years ago, a billion years after the solar system formed, it was well established there and has since evolved into the lush abundance of complex forms seen today. Mars, meanwhile, became a freezing desert.The question nevertheless remains: given that the conditions needed for life to emerge on Earth also seem to have pertained for a time on Mars, might life have evolved there, too? And, if it did, might it still survive in some form, even if only in vanishingly rare amounts?