Science from the Extended Mission of the Phoenix Mars Lander

NASA's Phoenix Lander landed on 25-May-2008 in the polar environment of Mars at 68 degrees north, and has taken a close-up look at Mars' surface. The nominal mission was set to last about 3 months, but the mission is still going and has been extended. It will probably keep going until Martian winter closes in, in early 2009. Our work will capitalize on the results to date and support the extended mission operations. Phoenix has a robotic arm, which digs into the ground, and has found ice lying just 5-10 cm below the surface. It has also scooped up samples for analysis and measured the local climate with weather sensors. The overall purpose is to look for clues about where the ice came from, what the soil is made of, and whether microbes might have lived in Mars' early history. Our contribution to the mission will help understand Mars in three ways. Firstly, we will analyze microscopic pictures of the soil particles and use this knowledge to suggest where the lander should scoop up further samples in its extended mission so that we can learn more. We will examine these pictures to determine whether the soil was once deposited from sediments in a lake or sea, carried there by the wind, thrown up by asteroid impact, or came from the erosion and break down of volcanic rocks. Secondly, Phoenix has an experiment where soil scooped up by the robotic arm is mixed with water. Salts in the soil dissolve and probes measure the type of salts, for example whether sodium chloride is present, the salt people use on food. So far, the experiment has discovered that the soil is slightly alkaline, very like that of seawater, and contains components such as magnesium, potassium, and sodium. By analyzing the data further and considering it in detail, we hope to determine whether the salts on Mars were left behind when water dried up or whether the salts came from more recent chemical reactions in the atmosphere and soil. Thirdly, when the Phoenix spacecraft fell to the surface of Mars from space it was slowed down by friction with the air. The rate that the lander decelerated depended on the air density and temperature. We have used the deceleration measurements for a preliminary calculation of how the air density and temperature changed with height. We found that the atmosphere below about 60 km height is unusually warm compared to predictions from the sort of computer models that are similar to those that predict weather on the Earth. We will do more detailed analysis to understand this discrepancy and learn information about the climate, for example, whether there were clouds present during landing or whether the air held lots of dust. We also hope to learn if the unusual atmosphere explains why Phoenix overshot its intended landing site. The microscopy station on Phoenix, that forms a large chunk of our research, consists of an optical microscope that takes colour and ultraviolet pictures and a very-high-resolution microscope called an atomic-force microscope, or AFM. The AFM can image the surfaces of particles smaller than the width of a human hair. These surfaces give us clues about how particles break down and some suggest the decay of volcanic minerals into clays. We plan to do some lab experiments to see if we can replicate on Earth some features seen on Mars. Our research is a great opportunity for a UK contribution to a high profile international Mars mission at modest cost. This research will therefore help to build up the UK's experience of landing on Mars and continue to bring Mars exploration to the UK public.