Studies of the surface and atmosphere of Mars from NASA's Phoenix Lander

这项工作将是美国国家航空航天局凤凰号着陆器任务的一部分，该任务将于2008年5月发射一艘航天器登陆火星，并近距离观察火星北极地区。那里有大量的冰，就在那里的表面之下。一只机械臂将挖掘地面，寻找冰从哪里来的线索，以及火星早期历史上是否存在微生物。我们对这项任务的贡献将从三个方面帮助理解火星。首先，我们将确保用显微镜尽可能好地拍摄火星北极的土壤和冰的照片。我们将检查这些图片，以确定土壤是否曾经是从湖泊或海洋的沉积物中沉积出来的，或者是被风吹到那里的，或者直接来自火山熔岩的侵蚀和分解。其次，当凤凰号航天器从太空坠落到火星表面时，它会因与空气的摩擦而减速。着陆器减速的大小取决于气压和温度。我们将使用凤凰号着陆器测得的减速来计算气压和温度如何随高度变化。这可以告诉我们有关气候的信息，例如，着陆过程中是否存在云层，或者空气是否干燥并带有大量灰尘。第三，凤凰号着陆器进行了一项实验，通过机械臂将土壤铲起，并与水混合。土壤中的盐会溶解在水中，溶液中的探测器将测量盐的类型，例如是否存在氯化钠，即人们用于食物的盐。我们希望找出火星上的盐分是在一大片海洋干涸时留下的，还是来自火山气体与土壤的化学反应。凤凰城上的显微镜站构成了我们研究的一大部分，由一台传统的光学显微镜和一台名为原子力显微镜或AFM的超高分辨率显微镜组成。这个显微镜站最初是由汤姆·派克博士在加州NASA喷气推进实验室工作时建造的。尽管显微镜站已经建成，但原计划在2001年将显微镜站送到火星赤道的着陆器被取消了。然而，它现在将于2007年飞往火星北极。火星北极的不同条件意味着显微镜站将不得不以不同的方式运行，而不是最初的设计。这项工作将把显微镜站的副本放入模拟室。各种冰和土壤样本将从机器人手臂铲子的副本中投入空间站，并用光学显微镜和原子力显微镜拍摄显微镜图像。起初需要一些人工干预以确保拍摄到良好的图像，但随着空间站经验的积累，越来越多的操作将通过计算机控制自动执行。最终，显微镜站将能够自己拍摄良好的图像，就像它将在火星上所做的那样。这些自动操作的方法或算法将被内置到凤凰号任务中用于控制显微镜站的计算机代码中。样品将被带到专门挑选的支架上的显微镜下。使用与制造硅片类似的技术，将有可能切割一些硅，以便最好地制造用于显微镜成像的小冰和土壤颗粒的支架。我们的研究是一个独特的机会，让英国以适度的成本为一个重要的国际火星探索计划做出贡献。因此，这项研究将有助于建立英国有限的登陆火星的经验，并将火星探索的兴奋带给英国公众。

This work will be part of NASA's Phoenix Lander Mission, which will send a spacecraft to lands Mars in May 2008 and take a close-up look of the Martian northern polar region. Large amounts ice lie just below the surface there. A robotic arm will dig into the ground, looking for clues about where the ice came from 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 ensure that microscopes take the best possible pictures of the soil and ice in the Martian arctic. We will examine those pictures to determine whether the soil was once deposited from sediments in a lake or sea, or carried there by the wind, or came directly from the erosion and break down of volcanic lava. Secondly, when the Phoenix spacecraft falls to the surface of Mars from space it gets slowed down by friction with the air and decelerates. The amount that the lander decelerates depends on the air pressure and temperature. We will use the measured deceleration of the Phoenix lander to calculate how the air pressure and temperature changes with height. This can tell us information about the climate, for example, whether there were clouds present during landing or whether the air was dry with a lot of dust. Thirdly, the Phoenix lander has an experiment where soil is scooped up by the robotic arm and mixed with water. Salts in the soil will dissolve in the water and probes in the solution will measure the type of salts, for example whether sodium chloride is present, the salt people use for food. We hope to find out whether the salts on Mars were left behind when a big sea dried up or whether they come from the chemical reaction of volcanic gases with the soil. The microscopy station on Phoenix, that forms a large chunk of our research, consists of a conventional optical microscope and a very-high-resolution microscope called an atomic-force microscope, or AFM. This microscopy station was originally built by Dr Tom Pike while working at NASA's Jet Propulsion Laboratory in California. Although the microscopy station was completed, the lander that would have carried the microscopy station to the equator of Mars in 2001 was cancelled. However, it will now fly to the Martian arctic in 2007. The different conditions of the Martian artic mean the microscopy station will have to be operated in different ways to its original design. This work will put a copy of the microscopy station into a simulation chamber. Various ice and soil samples will be dropped from a copy of the robot-arm scoop into the station, and microscope images taken with the optical microscope and AFM. At first there will need to be some human intervention to ensure that good images are taken, but as experience with the station is built up more and more of the operations will be performed automatically through computer control. Eventually the microscopy station will be able to take good images by itself, as it will have to on Mars. These methods for automatic operation, or algorithms, will be built into the computer code used on the Phoenix mission to control the microscopy station. The samples will be carried to the microscopes on specially selected holders. Using techniques similar to those used to make silicon chips, it will be possible to cut some silicon so as to best make holders for the small ice and soil particles for microscope imaging. Our research is a unique opportunity for a UK contribution to an important international Mars exploration programme at a modest cost. This research will therefore help build up the UK's limited experience of landing on Mars and bring the excitement of Mars exploration to the British public.