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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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God of commerce, travel and thievery

general information
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
planetary statistics
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)
planetary statistics1
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
mercury surficial features
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
early investigations
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
early satellite exploration
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
mariner 10 cont d
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
mercury internal structure
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
surface features and processes
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
tectonics santa maria rupes
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
caloris basin
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
tectonics weird terrain
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
planetary geologic evolution
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
mercury s evolutionary factors
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
messenger s mission timeline
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
messenger new images
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
messenger new images1
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
mdis highest res color image even acquired
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
mercury s geological history cont d
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