Onward to Europa
The oceans of Jupiter's ice worlds might be swimming with life — so why do we keep sending robots to Mars?
Europa, one of Jupiter's moons.
The robots come to Mars out of a sky tinged peach from whirlwind-lofted dust. They cut through the thin, cold air in supersonic aeroshells and parachutes, making planetfall in bouncing airbag cocoons and bursts of braking retrorockets, bristling with cameras and spectrometers, antennas and manipulator arms. Some stay where they land; others rove for years on end. Sniffing the air, sifting through soil, wheeling across a cratered landscape, the robots doggedly seek any wisp of Martian moisture, like lost desert travellers dying of thirst. They are looking for life, following a strategy that NASA officials describe as ‘following the water’.
This strategy pays heed to water’s eerie harmony with life: wherever one is found on Earth, the other isn’t far behind. There are good reasons to believe that water is the ideal cornerstone of biology, not only on Earth, but elsewhere in the Universe. All you need to make it is hydrogen and oxygen, respectively the first and third most abundant elements in the cosmos.
In liquid form, water is unparalleled in its attunement to life’s needs. It facilitates the transmission of biochemical energy, nutrients, and waste. It shapes the structures and interactions of proteins and other macromolecules. It shields against hostile cosmic radiation, and it has a remarkably robust capacity for retaining warmth. Most strangely, unlike almost every other substance in the Universe, when water freezes, it expands instead of contracting, forming a protective, insulating shell of ice at its surface. This helps oceans, lakes, and other liquid reservoirs avoid freezing solid when exposed to prolonged cold.
For the rest of the story: http://aeon.co/magazine/nature-and-cosmos/its-time-to-look-for-life-in-europas-ocean/