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The search for water on Mars
The search for water on Mars

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4.8 Phoenix Lander – a better look at the polar region

You will recall that the poles were one of the first places suggested to have evidence of water, and several orbiter missions have confirmed this. Yet, until the Phoenix mission landed in the martian north polar region in 2008, these areas had not been investigated by ground-based spacecraft.

Phoenix was specifically designed to look for water and determine whether habitable areas might exist. When its robotic arm dug a trench into the soil, it found dice-sized clumps of bright material that vaporised over four days (Figure 44). Using its on-board instruments, this was confirmed as being water ice. Phoenix also observed water frost early on a morning, which disappeared as the Sun rose.

Phoenix also made two particularly important discoveries. Firstly, it confirmed the presence of perchlorate (ClO4−), which can act as an antifreeze (i.e., it can lower the freezing point of water), potentially allowing liquid water to exist. Secondly, it observed snow falling – the first time this was seen on Mars.

This figure consists of two photographs of the martian surface taken by the Phoenix lander, side by side. The left hand image is labelled Sol 20 and the right hand image is labelled Sol 24. Both images show a rectangular-shaped trench in the brown-coloured martian soil. The trench in the left hand image has small, dice-sized cubes towards one corner. These are absent in the right hand image. An inlay magnifying this area of the trench is shown.
Figure 44 Colour images taken by the Phoenix lander on the 21st and 25th days of the mission. A group of dice-sized pieces is visible in the lower left corner of the trench (left image), which disappeared after 4 days (right image). Image credit: NASA/JPL