NEEP602 Course Notes (Fall 1996)
Resources from Space
OBSERVABLES FOR PLANETS IN THE SOLAR SYSTEM
A. Having to do with size, shape, elevation.
1. Size and shape expressed using simple geometric parameters (e.g., polar and equatorial diameters, biaxial and triaxial figures).
2. Statistical topography % of surface at a particular elevation vs. Elevation, (e. g. see p. 49, Cattermole for comparisons of Earth , Venus and Mars).
3. Detailed topography; craters, mountains, depressions, faults, etc.
4. Geographical distribution of other physical parameters, e.g., maps of the height of a planet's equipotential surface (e.g., sea level on Earth).
B. Having to do with physical fields mapped at the surface, at depth, with height.
1. Temperature (average and seasonal) (Wein displacement law, which relates wave length of EM radiation maximum to temperature).
2. Heat flux out of the planet or into the planet from external sources (calories/cm2/sec); internal heat sources are gravitational collapse and radioactive decay , (depends on T4, Boltzman constant).
3. Gravitational field strength patterns i.e. anomalies.
Anomalies are the difference between the observed value and the expected value at a position based on latitude, elevation, and mass in milli-gals (mgls), a gal = 1 cm/sec2 or by mass concentrations or interms of local deviations of gravity based on the shape of an equipotential surface as sensed by the motions of orbiting space craft (Masscons).
4. Magnetic field strength (gammas = 10-5 gauss = 1 nano-tesla). On Earth 98% dipolar field originates in electric currents flowing in the molten conductive core.
5. Conductivity, resistivity of rocks.
6. Elastic (seismic) waves which can be related to rock type and rheology, e. g. nonexistence of shear waves in the liquid core, Vs = 0.
C. Having to do with age.
1. Absolute, which for rocks usually means time since radioactive motherand daughter products last separated.
2. Relative age, which speaks about the secession of events, e.g., for undisturbed layers of sediment on the sea floor where the youngest is on top, or for overlapping craters where the youngest is the one that is undisturbed.
D. Having to do with rocks.
1. Rock types, origin, history (extrusive or intrusive, skippers or nonskippers, Sial and Sima, etc., etc.)
2. Strength of rocks (depends on rock type, time, temperature, pressure, and presence of water). Lithosphere (a region capable of maintaining its shape under long term stress and sustaining abrupt rupture i.e. quakes) ; asthenosphere (a region which flows under long term stress). Note: crust and upper mantle are usually found to be lithospheric while lower parts of the mantle are generally asthenospheric.
E. Having to do with planetary motion.
1. Rotation refers to angle of rotation axis to a plane; (usually the plane of the Earth Moon system about the sun, the plane of the ecliptic) .
2. Revolution refers motion about the sun.
3. (Smoothness of motion as a determinant to unseen orbital partners).
F. Having to do with existence and condition of an atmosphere.
1. Gases present, speciation with height, temperature, pressure and motion. (See Cattermole for comparison of Venus and Earth, p 41.)
2. Control exerted by these on atmospheric transparency to UV and IR (greenhouse). (See Kastings etal., 1988 and Lovelock, 1990).
Most indirect measurements depend on spectra (intensity vs wave length) of electo-magnetic waves (light, heat, uv).
1. Identification of rocks and minerals on planetary surfaces.
2. Identification of gases in planetary atmospheres.
3. Estimates of temperature (See Cattermole, p 41.), and other physical properties including motion.
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