[1] The optical microscope onboard the Phoenix spacecraft has returned color images (4 mm pixel −1 ) of soils that were delivered to and held on various substrates. A preliminary taxonomy of Phoenix soil particles, based on color, size, and shape, identifies the following particle types [generic names in brackets]: (1) reddish fines, mostly unresolved, that are spectrally similar to (though slightly darker than) global airborne dust [red fines], (2) silt-to sand-sized brownish grains [brown sand], (3) silt-to sand-sized black grains [black sand], and (4) small amounts of whitish fines, possibly salts [white fines]. Most particles have a saturation magnetization in the range 0.5-2 Am 2 kg −1 as inferred from their interaction with magnetic substrates. The particle size distribution has two distinct peaks below 10 mm (fines) and in the range 20-100 mm (grains), respectively, and is different from that of ripple soils in Gusev crater. In particular medium to large sand grains appear to be absent in Phoenix soils. Most sand grains have subrounded shape with variable texture. A fractured grain (observed on sol 112) reveals evidence of micrometer-sized crystal facets. The brown sand category displays a large diversity in color including shiny, almost colorless particles. Potential source regions for these grains may be the Tharsis volcanoes or Heimdal crater (20 km east of the landing site). The black grains are suggested to belong to a more widespread population of particles with mafic mineralogy. The absence of black/brown composite grains is consistent with different formation pathways and source regions for each grain type. Citation: Goetz, W., et al. (2010), Microscopy analysis of soils at the Phoenix landing site, Mars: Classification of soil particles and description of their optical and magnetic properties,

The first NASA scout mission to Mars, Phoenix, launched 4 August will land in the northern part of Mars in the locality of 68°N and 233°E on 25 May 2008. Part of the science payload is the Magnetic Properties Experiments (MPE) that consists of two main experiments: the Improved Sweep Magnet Experiment (ISWEEP) and 10 sets of two Microscopy, Electrochemistry, and Conductivity Analyzer (MECA) magnet substrates with embedded permanent magnets of different strength. The ISWEEP experiment is, as the name indicates, an improved version of the Sweep Magnet Experiments flown onboard the two Mars Exploration Rovers (MERs) Spirit and Opportunity. The sweep magnet is ring shaped and is designed to allow only nonmagnetic particles to enter a small circular area at the center of the surface of this structure. Results from this experiment have shown that on the MERs hardly any particles can be detected in the central area of this ring‐shaped magnet. From this we have concluded that essentially all particles in the Martian atmosphere are magnetic in the sense that they are attracted to permanent magnets. In order to improve the sensitivity of the Sweep Magnet Experiment for detection of nonmagnetic or very weakly magnetic particles, the ISWEEP holds six ring‐shaped magnets, somewhat larger than the sweep magnet of the MERs, and with six different background colors in the central area. The six different colors provide new possibilities for improved contrast between these background colors, i.e., any putative nonmagnetic particles should render these more easily detectable. The Surface Stereo Imager will also take advantage of the small clean areas in the ISWEEPs and use the presumably constant colors for radiometric calibration of images. The MECA magnets work as substrates in the MECA microscopy experiments; they are built to attract and hold magnetic particles from dust samples. The collected dust will then be examined by the optical microscope and the atomic force microscope in the MECA package.

[1] The Phoenix Robotic Arm Camera (RAC) is a variable-focus color camera mounted to the Robotic Arm (RA) of the Phoenix Mars Lander. It is designed to acquire both close-up images of the Martian surface and microscopic images (down to a scale of 23 mm/pixel) of material collected in the RA scoop. The mounting position at the end of the Robotic Arm allows the RAC to be actively positioned for imaging of targets not easily seen by the Stereo Surface Imager (SSI), such as excavated trench walls and targets under the Lander structure. Color information is acquired by illuminating the target with red, green, and blue light-emitting diodes. Digital terrain models (DTM) can be generated from RAC images acquired from different view points. This can provide high-resolution stereo information about fine details of the trench walls. The large stereo baseline possible with the arm can also provide a far-field DTM. The primary science objectives of the RAC are the search for subsurface soil/ice layering at the landing site and the characterization of scoop samples prior to delivery to other instruments on board Phoenix. The RAC shall also provide low-resolution panoramas in support of SSI activities and acquire images of the Lander deck for instrument and Lander check out. The camera design was inherited from the unsuccessful Mars Polar Lander mission (1999) and further developed for the (canceled) Mars Surveyor 2001 Lander (MSL01). Extensive testing and partial recalibration qualified the MSL01 RAC flight model for integration into the Phoenix science payload.

The Organic Free Blank (OFB) for the Mars 2007 Phoenix Scout mission provides an organic carbon null sample to compare against possible Martian organic signatures obtained by the Thermal and Evolved Gas Analyzer (TEGA). Major OFB requirements are an organic carbon content of ≤10 ng C g−1 of sample, a nonporous structure, and strength and integrity that permits machining by the Robotic Arm (RA) Icy Soil Acquisition Device (ISAD). A specially fabricated form of commercial Macor™ (a machinable glass ceramic), made with nitrate salts replacing carbonate salts, was selected as the OFB material. The OFB has a total inorganic carbon content of approximately 1.6 μg C g−1 after fabrication, cleaning, and heat treatment in oxygen gas at 550°C. The detection limit for organic carbon is ∼100 ng C g−1 of sample, or about a factor of 10 higher than the design goal. One scenario for OFB use on Mars is subsequent to the first TEGA detection of organic carbon. The OFB sample, acquired by the RA ISAD and delivered to TEGA, would come in contact with all surfaces in the sample transfer chain, collecting residual terrestrial contamination that accompanied the spacecraft to Mars. A second sample of the putative Martian organic‐bearing material would then be obtained and analyzed by TEGA. Different organic contents and/or different mass spectrometer fragmentation patterns between the OFB material and the two Martian samples would indicate that the detected organic carbon is indigenous to Mars.

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