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Mercury

Mercury. God of commerce, travel and thievery. General Information. Named after Roman fleet-footed messenger god Appeared to move quickly across the sky Closest planet to Sun Difficult to observe from Earth Never gets more than 28 degrees from Sun

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Mercury

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  1. Mercury God of commerce, travel and thievery

  2. General Information • Named after Roman fleet-footed messenger god • Appeared to move quickly across the sky • Closest planet to Sun • Difficult to observe from Earth • Never gets more than 28 degrees from Sun • Can only be viewed during day or just prior to sunrise or just after sunset • Low in sky means 10 X more atmosphere to penetrate than if Sun were directly overhead • Second smallest planet (after Pluto) • Smaller than Titan and Ganymede • Sun would appear 2 ½ X bigger in sky from the surface

  3. Planetary Statistics • Mean distance from Sun 57,910,000km • 0.38 A.U. • Highly eccentric (28.6 -43.5 million mi) • Orbital Period = 87.96 days • Rotational Period = 58.6 days • Spin-orbit coupling • 2 years to exactly 3 days • Axis Tilt = 0.01 degrees (23.5) • Diameter = 4880km (12,756km) • Mass = 3.303 x 1023 (5.97 x 1024) • (.05527 of Earth) • Density = 5.42gm/cm3 (5.515gm/cm3)

  4. Planetary Statistics • Equatorial surface gravity = 2.78m/sec2 (9.78m/sec2) • Visual albedo = 0.10 (.37) • Moons = none • Surface = heavily cratered • Atmosphere = atoms blasted off surface by fierce solar wind • Very, very thin • Composition • Helium 42% • Sodium 42% • Oxygen 15% • Mean surface temperature = 170C (330F) • Max temp = 427C (870F) • Min temp = -173C (-360F) • Most extreme in our SS

  5. Mercury – Surficial Features • Heavily cratered surface • Represents geological record of SS impact rates • Infers no erosional or depositional geologic processes throughout planets history • Infers extremely thin atmosphere • No liquid water • Fault scarps • Demonstrate vertical and some horizontal tectonic movement • Can be 100’s of kms in length and > 2mi high • Probably due to planets cooling history • Heating/expansion = normal faulting (tensional stress) • Cooling/contraction = reverse (compress. stress) • Some may be result of larger impact events • Focus of seismic waves antipodal to impact point

  6. Early Investigations • Giovanni Schiaparelli • 1880’s sketched faint features from telescopic observations • Suggested Mercury tidally locked to Sun • Much like the Moon is to Earth • Pettengill and Dyce • 1965 determined Mercury’s rotational period proving it is not tidally locked • Speculation rotation was perhaps as quick as 8 hrs • Slowly despun over 109 yrs • Raised interior temp by 100K • Einstein’s Theory of Relativity • Newtonian mechanics didn’t fit orbital characteristics • Once thought another planet (Vulcan) was reason for orbital perturbations • Correctly predicted the precession (very slowly moves backward) of the perihelion of Mercury

  7. Early Satellite Exploration • Mariner 10 was the 7th successful launch in the Mariner spacecraft series, and the first to use the gravitational pull of one planet (Venus) to reach another (Mercury) • Instruments on board the spacecraft were designed to measure the atmospheric, surface, and physical characteristics of Mercury and Venus • Experiments included: • Television photography • Magnetic field • Plasma • Infrared radiometry • Ultraviolet spectroscopy • Radio science detectors • An experimental X-band, high-frequency transmitter was flown for the first time on the spacecraft

  8. Mariner 10 (cont’d) • Mariner 10 reached Mercury on March 29, 1974, passing over the planet at 705 kms (438 mi) above the surface • Made a total of three passes during 1974-75 • Photographs revealed an intensely cratered, Moon-like surface, a faint atmosphere • Engineering tests were continued until March 24, 1975, when the supply of attitude-control gas was depleted and the mission was terminated

  9. Mercury – Internal structure • About 1/3 the size of Earth • Density is comparable to that of Earth • Indicates that Mercury has a large core roughly the size of Earth's Moon or about 75% of the planet's radius • The core is likely composed of 60 to 70% iron • Mariner 10's measurements reveal a dipolar magnetic field • Possibly produced by a partially molten core • Solid rocky mantle surrounds the core • Thin silicate crust of about 100 kms

  10. Surface Features and Processes • Craters • Range from 100m– to 1,300km in diameter • Caloris Basin • Largest multi-ring basin on Mercury • 100km diameter asteroid • Concentric mountain rings 3km high • Ejecta blanket covers 600-800km • Lava flows • Post-accretion phase volcanic activity • After crustal cooling 3rd phase of flows producing smooth plains • Scarps • 2nd phase tectonics • Thrust faulting • Contraction and shrinking of silicate crust • Water? • 1991 radio waves from Caltech scientists yield bright returns at north pole • Axial tilt low = no sun on crater interiors = temp <161C • Possibility of ice at or very near surface

  11. Tectonics – Santa Maria Rupes • Sinuous dark feature running through the crater at the center of this image • Interpreted to be enormous thrust faults • Indicate that the radius of Mercury decreased by 1-2 kms after the solidification and bombardment of the surface • Volume change probably was due to the cooling of the planet, following the formation of a metallic core three-fourths the size of the planet

  12. Caloris Basin • Mariner 10 mosaic • Terminator enhances relief • Note at least 3 concentric rings • Many ring mountain blocks are over 3 kms high • Secondary mountain rings likely created by impact shock waves • Radiating outward are systems of valleys, hills, and other craters • Secondary craters surround the Basin • Some are in excess of 20 kms diameter • The Caloris Basin interior is filled with mostly smooth plains most probably volcanic in nature

  13. Tectonics – “Weird Terrain” • Hilly, lineated region of Mercury at the antipodal point from the Caloris Basin • The shock wave from the Caloris impact was reflected and focused to this antipodal point • Result was jumbled crust broken into a series of complex blocks • Note orthogonal fracture systems • The area covered is about 100 kms (62 mi) on a side

  14. Planetary Geologic Evolution • Size • Mass • Radius • Chemical Composition • Three general phases • Highly active • Crustal formation and mobility • Volcanic • Accompanys thickening sub-crustal lithosphere • Terminal quiescent • Lithosphere too thick to allow volcanism or lateral movement

  15. Mercury’s Evolutionary Factors • Important reference point • Planet closest to the Sun • Solar wind does not allow substantial atmosphere to form • End-member of chemical composition • High temperature • Refractory elements • Few volatiles • Larger than Moon evolving at slightly different tempo • Mercury • ~Same mass and surface gravity as Mars • ~Same bulk density of Earth

  16. Messenger’s Mission Timeline • KEY EVENTS:August 3, 2004 -- MESSENGER Launch August 2005 -- Earth flybyOctober 2006 -- Venus flybyJune 2007 -- Venus flybyJanuary 2008 -- Mercury flybyOctober 2008 -- Mercury flybySeptember 2009 -- Mercury flybyMarch 2011 -- Yearlong science orbit of Mercury begins

  17. Messenger (New Images) • Like the previously mapped portion of Mercury, this hemisphere appears heavily cratered • Upper right, Caloris basin, including its western portions never before seen by spacecraft • Caloris is one of the largest, and perhaps one of the youngest, basins in the Solar System • New image shows the complete basin interior and reveals that it is brighter than the surrounding regions and may therefore have a different composition • Darker smooth plains surround Caloris, and many unusual dark-rimmed craters are observed inside the basin • Several other multi-ringed basins are seen in this image for the first time • Prominent fault scarps (large ridges) lace the newly viewed region

  18. Messenger (New Images) • One of the highest and longest scarps (cliffs) yet seen on Mercury • (The Sun is shining low from the right, so the scarp casts a wide shadow) • Compressional tectonic forces in Mercury’s crust have thrust the terrain occupying the right two-thirds of the picture up and over the terrain to the left This image was taken from a distance of only 5,800 kilometers (3,600 miles) from surface of the planet and shows a region about 200 kilometers (about 125 miles) across

  19. MDIS – highest res color image even acquired • Closest approach, just 200 kms above the surface • (500 meters/pixel • 120-km diameter Rudaki Crater • Younger smooth surface on left • Older rougher, bluish terrain on right • Orange crater rim • Blue-floored crater • Dark blue material was ejected from the 105-km diameter crater on the right side • A relatively young, small crater then excavated through this blue material to reveal the smooth plains beneath

  20. Time lapse photo of Mercury over Leeds, England

  21. Mercury’s Geological History (cont’d) • This scene is near Mercury's terminator where shadows are long and accentuating height differences • Note: • Concentric rings • Smooth basin floor • Large, chaotic ejecta blanket • Large number of secondary linear crater chains • The large crater is Sullivan crater, a structure about 135 kilometers (84 miles) in diameter also seen during the Mariner 10 mission Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

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