 EFFECTS OF MARTIAN SURFACE MATERIALS ON THE THERMAL DECOMPOSITION OF HYDROGEN PEROXIDE.  R. H. Dame1,  P. D. Archer Jr.2 and J. V. Hogancamp3,1Department of Physics and Astronomy, Brigham Young University, Provo, UT 84602, 2Jacobs, NASA Johnson Space Center, Houston, TX 77058. 3Geocontrols Systems Inc., NASA Johnson Space Center, Houston, TX 77058. Introduction:   While hydrogen peroxide (H2O2) has been detected in the martian atmosphere, it has not yet  been detected in surface materials  [1].  Hydrogen peroxide is a powerful oxidant and is destructive to organic  molecules;  thus,  knowledge  of  its  presence would be very useful for future missions with respect to understanding the potential  for the survival  of organic molecules and for potential life on Mars. Since the Viking lander mission, we have sent instruments to Mars with the capability to detect H2O2.  The Sample Analysis at Mars (SAM) instrument on board the Curiosity rover and  Thermal and Evolved Gas Analyzer (TEGA)  instrument  on  the  Phoenix  lander  both  detected water and oxygen releases from analyzed sediments. Whether or not peroxide could be the source of these gases has not been investigated through laboratory experiments. In this study, Mars-relevant minerals were mixed with hydrogen peroxide and studied using a SAM/TEGA analog laboratory instrument in order to determine the potential for H2O2 in martian surface materials. In  studies  of  perchlorates  on  Mars,  it  was  found that  perchlorates  alone  have  higher  oxygen  release temperatures  than  the  SAM-analyzed  samples  from Gale Crater. Therefore, the O2 releases could not have been due to perchlorates alone. It has also been determined  that  when  mixing  Mars  analogue  iron-phase minerals with perchlorates, the oxygen release temperatures were lowered into the gas release temperature range similar to the gas release temperature of the Gale crater samples[2,3]. Hydrogen peroxide alone decomposes to H2O and O2, with the peak of the decomposition around 100 °C (Fig. 1).  This is lower than the O2 releases  detected  with  SAM  or  TEGA,  but,  as  described with perchlorates, the presence of other minerals can affect decomposition temperatures.  Therefore, we hypothesized that other minerals could alter peroxide decomposition behavior and we could compare lab data to results from Mars to determine whether or not hydrogen peroxide could have been present in the samples analyzed on Mars. Materials  and Methods:   ~20 mg of  hematite, siderite,  San  Carlos  forsterite,  pyrrhotite,  magnetite and nontronite (representing a broad range of minerals relevant to Mars) were mixed with 5µl 50% H2O2, and were either run immediately or placed in a sealed tube for 2, 4, or 9 days to look for changes over time. Eight samples of each mineral were made so that there would be two reps for each exposure time. The mineral and hydrogen peroxide were mixed using a dental tool to insure even distribution of the H2O2,  after which the samples were then stored in sealed tubes and left  in room temperature for their assigned exposure time. The samples  were analyzed in  a  Setaram Sensys Evo  differential  scanning  calorimeter  (DSC)  instrument connected to a mass spectrometer to detect the gases  released  from  the  sample.  The  furnace  was purged with a helium carrier gas at a pressure of ~30 mbar, and helium gas flow rate of 3 ml/min. Each sample was heated from -60 °C to 500 °C at a rate of 20 °C/min.  As a control, ~5 µl of 50% H2O2 was also run following the same procedure.  Each  mineral  was  analyzed  with  a  Panalytical X'pert pro X-ray diffractometer with a Co Kα X-ray source  to  look  for  changes  in  mineralogy.  A 50  mg sample of each analog mineral was mixed with 12.5 µl Figure 1. The gas release temperature of (a) water and (b) oxygen for a sample of 5µl 50% H2O2 . 2θ step with 1 min per step [4]. 50% H2O2  and left in a sealed tube for 10+ days. Samples were analyzed at 45 kV and 40 mA with a 0.02° Results  and  Discussion:   The  results  and  data from both evolved gas and XRD are as follows: EGA:  Hydrogen peroxide  alone  has  oxygen and water release temperatures that peak around the 100 °C (Fig. 1).   The nontronite and hematite  EGA samples data shows that as the exposure time of the samples increased,  the  oxygen  and  water  gas  releases  did  not change.  For  the  magnetite  samples,  the  oxygen  and water release temperatures slowly decreased as exposure time increased (Fig 2). The magnitude of the gas releases also decreases as the exposure time increases. The San Carlos forsterite samples also have a decrease in oxygen gas releases as time exposure increases and only a slight shift to lower temperature (not shown); its water gas release temperature shifts slightly to lower temperature  but  maintains  roughly  the  same  magnitude. When mixing the siderite sample and H2O2  the mixture visible reacted. The siderite EGA sample data shows that the mixing decreased the gas release temperature but all the exposure time samples had similar release temperatures.   Figure 2. The gas release temperature of (a) water and (b) oxygen for the mineral magnetite with varying time exposure. The results from the EGA data show that  mixing these  minerals  and  hydrogen  peroxide  can  cause  a lower gas release temperature over time, a decrease in the gas release magnitude over time or no change. XRD:  Samples  of  unaltered minerals were compared with the samples with 10-12 days of exposure to 12.5 µl 50% H2O2. Hematite, magnetite, nontronite and siderite samples did not display changes in mineralogy which was particularly surprising for the siderite which visibly  reacted  with  the  peroxide  when  mixed.  The XRD analysis showed that the mineralogy of pyrrhotite and San  Carlos  forsterite  changed when mixed  with hydrogen peroxide. The change of the pyrrhotite was most  dramatic.  The  results  showed  that  the  sample went from being pure pyrrhotite to being about 56% pyrrhotite and 44% iron sulfate hydrate (Fig. 4). Conclusions:   Preliminary results show three potential outcomes of the peroxide/mineral mixtures: 1) no  noticeable  effect  on  the  peroxide  or  the  sample (e.g., hematite, nontronite), 2) the mineral is unaffected but  catalyzes  peroxide  decomposition  (magnetite, siderite), or 3) peroxide alters the mineral (pyrrhotite, San Carlos forsterite).  In all of these cases, if peroxide decomposition  changed,  the  O2/H2O  releases  were shifted to slightly lower, not higher temperature, making it less likely that peroxides have been present in martian samples. References:  [1]  Clancy et al. (2004) Icarus, 168, 116-121.  [2] Sutter  et  al.  (2015)  LPSC XLVI,  Abst. #2137.  [3] Sutter  et  al.  (2013)  LPSC  XLIV,  Abst. #2046.  [4] Peretyazhko et  al.  (2016)  Geochemica  er Cosmochimica Acta, 188, 284-496. 
