The copybook landing of Phoenix, Nasa’s robotic geologist, on Mars breaks a jinx with Mars-bound spacecraft, considering the Red Planet’s reputation of being a graveyard for exploratory spacecraft. Since 1960, of the 38 probes launched from Earth towards that planet, only nine completed their mission. The others were outright failures, thanks to reasons ranging from the unexpected (as when a Martian storm destroyed Nasa’s Polar Lander during touchdown in 1999), to the bizarre (when careless mission controllers mixed up metric and imperial data and smashed the Mars Climate Orbiter against the planet’s atmosphere).
Since many of the probes were lost while trying to ‘bounce’ down on the planet, Nasa played it safe this time round, relying on retrorockets to make a soft touchdown. Equipped with several cameras and sophisticated instruments, Phoenix will seek out indications of water – past or present — on Mars. Billions of years ago, Mars and Earth were quite alike, with warm oceans, rain, and similar atmospheric systems. It’s a big puzzle that despite all this, life started on one planet while the other became dry and cold. Mars’ oceans presumably disappeared when the planet went through a hydrological cycle and became cold enough for water to freeze. These cycles of millions of years are caused by the wobble of the Martian axis. As on Earth, the water could have escaped into the atmosphere, or frozen out near the poles and emerged onto the surface in warmer times to cut the sharp channels we see in the images sent back by spacecraft. So it is likely that there are enormous quantities of ice beneath the surface in Mars’ polar regions — enough to deluge the planet if melted.
This entombed frozen water must have accumulated in winter and sublimed, or evaporated, in summer in each hemisphere. For ice doesn’t melt into liquid water on Mars. It sublimes — changing directly from solid to gaseous state — like ‘dry ice’ does on Earth. Much now depends on Phoenix’s robot arm digging through layers of soil to find this ice — and make what will be the most important announcement in space exploration since Galileo peered through a telescope.