Phoenix mission

On May 25, 2008, the mission landed and began to investigate samples. The mass spectrometer obtained spectra of atmospheric constituents, and measured the evolved gas from multiple samples collected directly in front of the lander [82,83]. It was critical in the potential discovery of calcium carbonate in surface material when it was used in peak mode to identify when CO2 was evolved. A significant increase in the concentration of CO2 was detected from a sample named Wicked Witch when the oven temperature approached 1200°C [82]. In the discovery of perchlorate in the Martian regolith, TEGA identified the evolved mass from O2 in a sample named Baby Bear. The onset of evolved O2 at 325°C and a peak at 465°C, which is consistent with the thermal decomposition of perchlorate [84]. These two discoveries, along with the measurement of the Ph and identification of precipitation from water ice clouds were highlights of the Phoenix mission [85]. 

The NASA supported development of the in situ Chemical Analysis Laboratory and Sensor Array (CHEMSENS) is based on the Phoenix WCL and will provide for real-time investigation of the soil on Mars and similar planetary settings. Though the Phoenix mission is viewed as highly successful and is stiU providing results years after the end of the mission, it was clear that improvements could be made for future missions. These included (1) the number of individual WCL units, (2) an increased number of sensors in the array, and (3) sensor redundancy. Incorporating these improvements resulted in a scalable payload of mini-WCL units with a movable gantry for sample delivery and various actuator assemblies. This will allow for a payload of a few or a hundred WCL units to be incorporated into a lander or rover. 

Fig. 6.9 A comparison of the sensor housing used in WCL and developed for CHEMSENS. The sensor housing on the left is similar to that used during the Phoenix mission housed in the WCL beakers. The middle housing was an initial prototype, and the housing on the right is the current housing used for the ISEs for the CHEMSENS project. Courtesy of McElhoney ITufts...

The NERNST concept applies several lessons learned from the Phoenix mission in order to provide a more robust, sensitive, and accurate measurement of the martian regolith. With NERNST, a sample of martian soil is first mixed with water off-chip in a sample extraction hub, and then the sample leachate (the water separated from the soil-water mix) is pumped on-chip for analysis. The sample can then be manipulated (with acid/base, BaCl2, etc.) and measured multiple times with multiple electrodes in order to provide a deeper understanding of the soluble chemistry of the soil sample. 

Figure 10.11 The ATM scanner from Nanosurf will be part of the miniaturised suite of microscopic instrumentation on the Phoenix space mission to Mars (Reproduced by permission of Nanosurf).

Hoffman, J.H., Chaney, R.C.,Hammack,H. (2008) Phoenix mars mission—the Thermal Evolved Gas Analyzer. Journal of the American Society for Mass Spectrometry, 79(10), 1377-1383. 

Later successful U.S. landers included the Mars Pathfinder lander/rover mission (which utilized air bags rather than retro-rockets during the last phase of its landing) and the Phoenix, which studied the geologic history of water on Mars, its involvement in Martian climate change, and the planet s past or future habitability. 

Spirit rovers) included mainly X-ray spectrometers and imagers. It was not until 2007 with the launch of the Phoenix Mars lander mission that the first electroan-alytical measurement system was delivered to the martian surface. Here we present the historical context of the first electroanalyses on Mars, an overall description of the electrochemically based sensors that were part of the Phoenix Wet Chemistry Laboratory (WCL), the results of the martian soil analyses and their implications, the most recent Earth-based experiments, and a preview of the next-generation electroanalytical instruments currently in development for upcoming missions to Mars and beyond. 

Another goal of the Phoenix WCL was to determine the presence and levels of soluble sulfate that had been suggested by previous Mars missions. Because no suitable ISE was available for the direct determination of S04 , the detection of S04 was accomplished by using a Ba " ISE to monitor the concentration of Ba (added as BaCl2) used to precipitate the S04 in the soil/solution mixture. In the presence of sulfate, the soluble Ba " immediately precipitates due to the highly selective and rapid formation of BaS04. As the precipitation occurs there is a decrease in the measured amount of Ba " and increase in the amount of Cl . 

Kounaves SP, HechtMH, Kapit J etal(2010) Wet Chemistry experiments on the 2007 Phoenix Mars Scout Lander mission Data analysis and results. J Geophys Res 115 EOOE10. doi 10. 1029/2009JE003424... 

---