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Sensing techniques in planetary science • Camera/photography: takes images in visible, infrared and/or ultraviolet light. REMOTE • Radar: maps objects and their surface features (mountains/canyons, asteroids) by sending radio signals that bounce off the surface and timing their return. Some waves can penetrate surface subsurface imaging. REMOTE • Spectroscopy/Spectrometry: see below. REMOTE and DIRECT • Mass spectrometry: see below. DIRECT • Microscopy: visualizes super-small objects/features. Light microscopes have limited resolution; electron microscopes and scanning probe microscopes overcome that. DIRECT • Magnetometry: measure the strength and the direction of a magnetic field at a point in space. Think metal detector. DIRECT (Q: Can a magnetic field be detected remotely? ___________________ • Gravimetry: measurement of the strength and the direction of a gravitational field. DIRECT Spectroscopy • …study of interaction between matter and radiative energy • Radiative energy can be, for example: • Electromagnetic radiation (from microwave and up) • Particles, e.g. electrons or neutrons • Interaction can be, for example: • • • • Emission Absorption Scattering Reflection • Atomic or molecular composition of the sample is deduced from the spectrum • Challenge: separating spectra of different components • Physical presence of the sample is NOT needed but can be used: both REMOTE and DIRECT sensing. Mass Spectrometry • …identification of chemicals in a sample by measuring the mass-tocharge ratio and abundance of gas-phase ions. • Break molecules into charged fragments (=ionization) • Flying these fragments at high speed through a magnetic or electric field bends their trajectories: higher mass less bend; higher charge more bend • Detect particles separated by mass-to-charge ratio • Challenge: separating spectra of different components. Gas chromatography can be used pre-MS to separate mixtures and simplify MS analysis. • Physical presence of the sample is needed: DIRECT sensing Camera examples Instrument Spacecraft Properties MArs Hand Lens Imager (MAHLI) MSL Curiosity • 1600×1200 px true-color images • resolution of 14.5 µm/px • white and ultraviolet LED illumination • mechanical focusing from infinite to 1mm. High Resolution Mars • Imaging Science Reconnaissance Experiment Orbiter (HiRISE) (MRO) • 0.5 m reflecting telescope (largest ever on a deep space mission) resolution of 1 μrad (= 0.3 m from H=300 km) • three color bands: B-G, R, and NIR • makes stereo pairs Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) Rosetta • narrow-angle lens 700 mm • wide-angle lens 140 mm, • 2048×2048 px CCD chip Radar examples Instrument Spacecraft Properties Shallow Mars • Subsurface Radar Reconnaissance (SHARAD) Orbiter (MRO) detects finely spaced (~7m) interfaces at depths < 1km (e.g. for internal polar cap structure) • HF radio waves between 15 and 25 MHz • horizontal resolution of 0.3 to 3 km Comet Nucleus Sounding Experiment by Radiowave Transmission (CONSERT) Rosetta • will measure propagation of 90 MHz EM wave between the Philae lander and the Rosetta orbiter through the comet nucleus (to study the comet's internal structure) Spectrometer examples Instrument Spacecraft Properties Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) MRO • visible and NIR (370-3920 nm) • 544 channels (each 6.55 nm wide) • resolution 18 m at H=300 km • studies surface mineralogy of Mars – iron, oxides, phyllosilicates, and carbonates have characteristic NIR spectra Mars Climate Sounder (MCS) MRO • 1 visible/NIR channel (3003000 nm) • 8 far IR (12 to 50 μm) channels • measures T, P, H2O vapor and dust levels in the atmosphere of Mars (watch the horizon!) • makes daily global weather maps Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) Rosetta • will image comet nucleus in the IR • will search for IR spectra of molecules in the coma More spectrometer examples Instrument Spacecraft Properties Cassini's Composite Infrared Spectrometer (CIRS) Cassini • identifies gases glowing in the lower layers of the atmosphere from their IR spectra Dynamic Albedo MSL • pulsed sealed-tube neutron of Neutrons Curiosity source and detector (DAN) • measures hydrogen (= ice and water) at or near the Martian surface • provided by the Russian Federal Space Agency Chemistry and MSL • high energy IR (1067 nm) laser Camera Complex Curiosity pulse vaporizes small amount (ChemCam) of rock at a distance ≤ 7 m = Laser-Induced • the spectrum of emitted light Breakdown is recorded Spectroscopy • provides elemental (LIBS) + Remote compositions of rock and soil Micro Imager • coupled to a high-res camera (RMI) Mass spectrometer examples Instrument Spacecraft Properties The Ion and Neutral Mass Spectrometer (INMS) Cassini • studies ions and neutral particles in the upper atmospheres of Saturn and moons • analyzed Enceladus plumes by flying directly through them COmetary Secondary Ion Mass Analyzer (COSIMA) Rosetta • analyses the composition of dust particles by secondary ion mass spectrometry, after the surface is cleaned by indium ions Bonus: MRO HiRISE portrait of Curiosity Chemicals in the Solar System Note Log scale on the y-axis Chemicals in the Solar System • Hydrogen (H) • Exists as H2 gas at STP • Elemental H constitutes ~74% of mass of the Universe • Metallic H is a phase where it loses it electron and behaves as an electrical conductor, @~500 Gpa; can be liquid or solid • Helium (He) ~24% of mass of the Universe • Oxygen • O2 gas at STP • Elemental oxygen is a part of many rock-forming compounds • It is also a part of water (H2O) • Carbon • • • • Pure forms such as graphite and diamond Polymerizes! Basis for life as we know it. Carbon dioxide (CO2) gas (at STP) Hydrocarbons: methane CH3 abundant, ethane C2H5 OK, ethylene C2H4, propane C3H8, propylene C3H8 … higher complexity lower abundance • Nitrogen • N2 is a gas at STP • A part of ammonia (NH3/NH4+), hydrogen cyanide (HCN), cyanoacetylene (C3HN) etc. • Fe and Mg (planetary cores); metal oxides and silicates, sulfur (mantles and crusts). Life as we know it • Made of H, C, O, N, P, S • Building blocks of DNA: nucleotides • Building blocks of proteins: amino acids • Plants convert CO2 and H2O into glucose in the presence of light… etc. • Complexity! Although simplest organic molecules can form spontaneously from simpler inorganic constituents in right conditions… www.compoundchem.com/2014/07/25/planetatmospheres/ www.compoundchem.com/2014/07/25/planetatmospheres/ Interiors • Terrestrial planets and satellites: Core, Mantle, Crust • Giants: Core, “Mantle”, Gas layer • Here “mantle” is an intermediate density, liquid- like transition layer between the core and the surface. • Interior not observable… • Observable qualities: mass, radius, gravity field, magnetic field, energy output, seismic activity • Density = mass/volume • <1 g/cm3 object is rich in ices, or is relatively porous, or has a gaseous composition • ~ 3 g/cm3 object is rocky • > 3 g/cm3 object has some metal content (iron, nickel, etc) • Shape depends on density, material strength, and plasticity Density of planets and selected moons Mean density (g/cm3) Sun 1.409 Mercury 5.430 Venus 5.240 Earth 5.515 Moon 3.346 Mars 3.940 Ceres 2.080 Jupiter 1.330 Io 3.528 Europa 3.010 Ganymede 1.936 Callisto 1.830 Saturn 0.700 Mimas 1.150 Enceladus 1.610 Tethys 0.984 Dione 1.480 Rhea 1.230 Titan 1.880 Iapetus 1.080 Uranus 1.300 Neptune 1.760 Proteus 1.300 Triton 2.061 Pluto 2.000 SS Body Magnetic fields • Origins of magnetic field: • Liquid metal in the core: differences in T & P cause convection (cool, dense matter sinks whilst warm, less dense matter rises) electric currents • Planet spin: the Coriolis force causes swirling whirlpools • Electric current + rotation = magnetism; typically aligned with the spin axis. • Magnetic moments and equatorial strengths of magnetic field (a strong refrigerator magnet is ~ 0.01 T): • Mercury: 2-6 × 1012 Tm3, Eq. strength = 300 nT (1.1% strength of Earth) • Earth: 7.91 × 1015 Tm3, Strength of 25-65 uT • Jupiter: 1.56 × 1020 Tm3, 428 uT (10x stronger than Earth; magnetic moment 18000x larger) • Ganymede: 1.3 × 1013 T·m3 , Eq. strength = 790 nT • Saturn: 4.6 × 1018 Tm3, 21 uT • Uranus: 10-110 uT. Misaligned w.r.t. spin axis (59) • Neptune: 2.2 × 1017 Tm3, 14 uT. Misaligned w.r.t. spin axis (47) • Why is magnetic field important? ________________________ ___________________________________________________ Planet interiors: terrestrial • Earth: iron-nickel core, solid + liquid, fast spin (24h) magnetic field; rocky mantle and crust • Moon: rocky mantle and crust, but possibly no iron core or strictly solid iron core ( no magnetic field) • Mercury: ~ Earth without most of the mantle. Slow spin (58d) magnetic field weak but detectable • Venus: similar to Earth, but a slow spinner (-243d, retrograde orbit) no magnetic field. • Mars: lower density more volatiles. Iron present on the surface and in the mantle, but magnetic field very weak and scattered. Planet interiors: giants • Jupiter: rocky/metal core, liquid metallic H, liquid molecular H, outer atmosphere (75%H2 / 24%He, traces of methane, water vapor, ammonia). • Ultra strong magnetic field! (liquid metallic hydrogen layer + very rapid spin rate = 9 hours, 50 minutes). • Internal heat: Jupiter releases more energy than it gets from the Sun (likely from its continuing “formation”, it has not yet cooled down). • Saturn: ~ Jupiter but less • Uranus/Neptune: not well understood. Possibly rocky core, icy mantle, gas outer atmosphere with significant fraction of methane ( blue/cyan). • Maybe a layer of conductive liquid ammonia/methane/water at a shallow depth ( magnetic field that is misaligned w.r.t. the spin axis). Interiors: selected dwarfs and moons • Jupiter’s “Galilean” Moons: • • • • Io Europa Ganymede Callisto • Saturn’s moons: • Enceladus • Titan • Ceres (asteroid belt dwarf) • Pluto (Kuiper belt dwarf) Events this week and on • Sun, Oct 19 – C/2013 A1 Siding Spring closest approach of Mars • http://mars.jpl.nasa.gov/comets/sidingspring/ http://www.nasa.gov/press/2014/october/nasa-prepares-its-science-fleet-foroct-19-mars-comet-encounter/ • Nights of Oct 20-21 and Oct 21-22 - Orionids (as Earth passes the orbit of 1P/Halley comet). Expect 20-25 shooting stars/hour. • http://www.timeanddate.com/astronomy/meteor-shower/orionid.html • https://solarsystem.nasa.gov/planets/orionids.cfm • Oct 23 – a partial solar eclipse with a maximum visible in SD at 3.33pm: • http://www.timeanddate.com/eclipse/in/usa/san-diego?iso=20141023 • http://eclipse.gsfc.nasa.gov/OH/OH2014.html#SE2014Oct23P • Nov 12 – Philae landing • Dec 13-14, 2014 – Geminids Meteor Shower Peak • Dec 31, 2014 – ESA Mars Express mission ends • Late March/early April 2015 – Dawn to arrive to Ceres • July 2015 – closest approach of Pluto by New Horizons References • Siobahn M. Morgan, Univ. of Iowa, course on Planetary Science: • http://www.uni.edu/morgans/planets/ • Cut-away models and other images by Calvin J. Hamilton: • http://www.solarviews.com/cap/index/index.html • http://www.solarviews.com/cap/index/cutawaymodels1 .html