The Phoenix has landed

Mankind once again makes its mark on the red planet, this time with the arrival of NASA's Phoenix lander. It successfully touched down yesterday in Mars's northern polar region and is reportedly in good health. The scientific mission will soon begin analysing the geology and climate of Mars, with particular emphasis on learning more about the history of water on the planet. One of its science packages is the meteorological station provided by the Canadian Space Agency (CSA), which includes a laser measurement device known as LIDAR that will be used to study atmospheric processes for the first time on another planet.

LIDAR is the acronym for Light Detection and Ranging, a technique similar to the better known RADAR commonly used for navigation in aviation and at sea. By using light instead of radio waves, however, LIDAR is capable of making far more discrete measurements due to the shorter wavelength of light.

The diode pumped Nd:YAG (neodymium-doped yttrium aluminium garnet) laser will emit a beam of pulses vertically into the atmosphere, at its fundamental wavelength of 1064nm (near infra-red) and at the frequency-doubled wavelength of 532 nm (green). Any light that is backscattered from particles in the atmosphere will be detected by a photodiode, using a telescope to maximise light capture.

Measurements of the time of arrival and the intensity of the backscattered light will provide information on the altitude and size of particles in the atmosphere. The measurement range extends up to a height of around 20km and it should be possible to measure the height of clouds to within a 10m accuracy, while the dual wavelength technique allows the system to distinguish between dust and ice particles.

It is always a feat of engineering to produce scientific payloads for use in space and on extra-terrestrial bodies, and the entire LIDAR package fits into a size no larger than a shoebox. It weighs in it at a mere 5kg and its peak power consumption is only 40W, comparable with that of a standard desktop lamp.

The LIDAR system will operate at frequent intervals throughout the Martian day for up to three months, shedding light on both the diurnal and seasonal variations in the atmosphere. Temperature and atmospheric pressure measurements made by the weather station will also contribute to a more comprehensive understanding of Martian weather patterns and the regular cycle between ice and water vapour.