Polar Volatiles Nov 7 2006 Adrienne Dove Brian Morsony Jessica Jones What s this all about The bottom line Does water ice exist at the lunar poles Historical context Observational evidence Theoretical considerations Looking towards the future A Smidgen of History First proposed by Watson Murray Brown 1961 Entirely theoretical Probability of permanently shadowed craters Demonstrated possible existence of ice in such craters Theoretical debates ensue for 30 years First observational evidence 1994 Clementine Arecibo and Clementine Coherent Backscatter Opposition Effect Key Characteristics Occurs with repeated scattering Light is reflected back towards the source Circular Polarization Ratio CPR 1 Mirror like CPR 0 Most geologic surfaces CPR 1 Important Examples Frozen volatiles Rough surfaces Greenland ice sheet Planetary regolith Icy moons Mercury Difficult to measure Receiver blocks the source Narrow backscattering cone Sensitive only to nearly pure water ice Arecibo and Clementine cont Arecibo 1992 125m resolution High CPR in Shackleton Crater Tentative but consistent with ice Clementine 1994 Not intended to look for water Measured CPR 25 increase over SP Nothing over NP Clementine Moon Deep Space Network antenna Lunar Prospector Neutron Spectrometer Fast Hot Medium Slow Cool Neutrons Sensitive to hydrogen in any form any purity H H2O Initial conclusion 10 to 300 million metric tons of water ice Later revised to 3 billion metric tons at each pole Medium energy 3 at SP 4 6 at NP Fast neutrons SP 5 000 20 000 km2 NP 10 000 50 000 km2 Outline How do you get water on the Moon How do you get it to stay there It s really not water How do you get water on the Moon Any primordial water would be gone Moon s gravity not high enough to retain water Comet impact creates temporary atmosphere Water will freeze in cold areas and fall to surface Becomes collected in cold traps Cold traps Water freezes out in cold areas Cold traps Subsequent small impacts mix ice into regolith How do you keep water on the Moon In the Sun the Moon is hot 395K Any ice sublimates away quickly At poles some craters are permanently shadowed Here temperature stays low 100K so ice is stable for long periods 2 billion years Permanent Shadows Why it s not water Lunar Prospector crashed into moon at end of mission Looking for water vapor and photodissociated hydroxyl OH Results absolutely NOTHING Possible explanations No water present just hydrogen Spacecraft completely missed the target site Spacecraft hit a dry spot within the crater Water exists in the form of hydrated minerals rather than free ice crystals energy of crash not enough to liberate Study of the aftermath was insufficient Theoretical models of the plume were inappropriate Telescopes pointed at the wrong location Plume didn t make it above the crater rim or went in an unobservable direction Why it s not water Radar data is ambiguous Other cases of CPR 1 Asteroids Maxwell Montes Venus SP lava flow Flagstaff AZ Polarization properties near poles could be due to water or surface characteristics New high resolution 20m radar images from Arecibo confirmed CPR 1 But show similar features in shadowed and nonshadowed craters Why it s not water Comparison of Shackelton crater top at 83 5 and Schomberger G crater at 70 Polarization associated with interior crater walls and ejecta not illumination conditions Polarization not due to water but there s hydrogen everywhere Where did it come from Why is it at the poles Solar wind Solar wind protons embed themselves in the lunar regolith Can bond to lunar material forming a hydroxyl OH group Probability of this happening depends on temperature of the material Material at poles is colder more of the time so tend to absorb the most hydrogen Summary No clear evidence for water ice on the moon If there is water it is likely a small part of the regolith 1 near the poles Current Future Missions Need to gain more understanding Does water ice exist If so where and how much Future missions need to Map location distribution and purity Robotic orbital missions can accomplish this to a point Will then need in situ measurements and experiments to verify SMART 1 ESA Small Missions for Advanced Research and Technology Polar elliptical orbit pericenter at SP region SIR SMART 1 infrared spectrometer Five topics Surface regolith processes lunar volcanism lunar crust structure ice spectral signatures at lunar poles ground geometric effects Map in NIR 0 9 2 4 microns using reflectance multiply scattered light Global coverage Passband includes some ice signature in 0 9 3 0 micron range Could detect H2O CO2 and CO ice frost CHANDRAYAAN 1 India India s first mission to the Moon Lunar polar orbiter Expected to launch in 2007 2008 will have a nominal 2yr mission Science includes High res mineralogical and chemical imaging of permanently shadowed north and south polar regions Search for surface or sub surface water ice on Moon esp at poles Instruments TMC HySI LLRI LEX HEX SXM MIP SARA M3 SIR 2 miniSAR radiation dose monitor Mini SAR Miniature Synthetic Aperture Radar John s Hopkins APL to detect water in permanently shadowed regions PSR s will transmit Right Circular Polarization RCP to surface Two modes scatterometer map scattering properties of lunar poles using backscattering receives RCP and Left Circular Polarization SAR mode measures RCP and LCP by delay Doppler methods Concentrated ice has Coherent Backscatter Opposition Effect CBOE increases reflectivity CPR in backscatter direction can detect 1 10m scale ice deposits under up to 40cm of dry regolith Will produce maps of lunar surface scattering properties help determine ice composition Combined with the laser altimeter will give better maps of the polar regions and PSR s Neutron flux map arrows indicate targets selected for SAR observations red high flux blue low flux LRO NASA Lunar Reconnaissance Orbiter Scheduled to launch Oct 2008 Overall objective is to obtain data that will be useful for future manned exploration of the Moon Will be in a circular polar orbit Instruments CRaTER DIVINER LAMP LEND LOLA and LROC Key related exploration points H mapping in certain polar regions mapping of all permanently shadowed regions LOLA One main objective to characterize the polar illumination environment image permanently shadowed polar regions This would aid in further exploration of shadowed regions to search for surface ice LEND Russian instrument Map neutron flux from lunar surface gives high