Mercury

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					Mercury and Venus
Mercury

                 Planet Profile:
Mass (kg)                                       3.3 x 1023
Diameter (km)                                   4879
Mean density (kg/m3)                            5420
Escape velocity (m/s)                           4300
Average distance from Sun                       0.387 au
Rotation period (length of day in Earth days)   58.65
Revolution period (year in Earth days)          87.97
Obliquity (tilt of axis degrees)                0
Orbit inclination (degrees)                     7
Orbit eccentricity (deviation from circular)    0.206
Mean surface temperature (K)                    452
Maximum surface temperature (K)                 700
Minimum surface temperature (K)                 100
Mercury



   Surface
       basalt and anorthosite
   Atmosphere
       Trace H and He
   Core?
       Global Magnetic field
       Dynamo?
  Visited by Mariner 10
This photomosaic of the planet Mercury was               QuickTime™ and a
assembled from individual high-resolution      TIFF (Un compressed) decompressor
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images taken by Mariner 10 shortly before
closest approach in 1974. The sun is shining
from the right, and the terminator is at
about 100 degrees west longitude. Crater
Kuiper, named after astronomer Gerard P.
Kuiper, can be seen just below the center of
the planet's illuminated side. The landscape
is dominated by large craters and basins
with extensive plains between craters.
    Caloris basin, 1350 km
                                                             QuickTime™ and a
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Seen here is part of the enormous Caloris             are neede d to se e this picture.
Basin, which is thought to be similar to the
large circular basins found on the moon.
Probably formed by a giant impact early in
Mercury's history, this basin was subsequently
filled by lava flows. The nature of the wrinkle
ridges on its floor is arguable: some scientists
claim tectonics while others suggest they are
due to volcanic flows escaping from fractures.
    Southwest Mercury
The southwest quadrant of Mercury is
seen in this image taken March 29,
1974, by the Mariner 10 spacecraft.                  QuickTime™ and a
The picture was taken four hours           TIFF (Un compressed) decompressor
before the time of closest approach           are neede d to se e this picture.
when Mariner was 198,000 km
(122,760 mi) from the planet. The
largest craters seen in this picture are
about 100 km (62 mi) in diameter.
      Hills of Mercury
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Weird terrain best describes this hilly,         are neede d to se e this picture.
lineated region of Mercury. Scientists note
that this area is at the antipodal point to
the large Caloris basin. The shock wave
produced by the Caloris impact may have
been reflected and focused to the
antipodal point, thus jumbling the crust
and breaking it into a series of complex
blocks. The area covered is about 800 km
(497 mi) on a side.
              QuickTime™ and a


          Messenger
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
             Why is Mercury so dense?                                             QuickTime™ and a
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                  • Uncompressed 5.3 g/cc
                  • Highest in solar system
                  • Twice Earth
             Geologic History
                  • Nebula accretion of lots of Fe (crust same comp)
                  • Boiled off (crust Ca, Al rich)
                  • Impacted off (crust depleted in Si, Al)

Launched Aug 2004, Swingby Earth & Venus to lose speed; Mercury orbit Mar 2011
Venus                                                                            QuickTime™ and a
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 Mass (kg)                                       4.87 x 1024

 Diameter (km)                                   12104
 Mean density (kg/m3)                            5250
 Escape velocity (m/s)                           10400
 Average distance from Sun                       0.723 au
 Rotation period (length of day in Earth days)   243.02 (retrograde)
 Revolution period (year in Earth days)          224.7
 Obliquity (tilt of axis degrees)                178
 Orbit inclination (degrees)                     3.39
 Orbit eccentricity (deviation from circular)    0.007
 Mean surface temperature (K)                    726
Venus
   Atmosphere
       96% CO2, 3 % N2, 0.1 % H2O
   Highest point
       17 km above planet radius
   Surface
       Basalt and altered materials
        Visitation                                                                         QuickTime™ an d a
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   Mariner 10 (1974)
       on way to Mercury (optical)
   Venera
       10 landings during 70s
                                                  Q uic kT ime ™ a n d a




    Magellan (1989)
                                      T IFF (U n co mp r e ss ed ) de c om p re s so r



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       Radar imagery of surface
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       Impact Craters
   Three large impact craters with
    diameters ranging from 37 km (23 mi)
    to 65 km (40 mi) are visible in the
    fractured plains. Features typical of
    meteorite impact craters are also
    visible. Rough radar-bright ejecta
    surrounds the perimeter of the craters;
    terraced inner walls and large central
    peaks can be seen. Crater floors appear
    dark because they are smooth and have
    been flooded by lava. Domes of
    probable volcanic origin can be seen in             QuickTime™ and a
    the southeastern corner. The domes        TIFF (Un compressed) decompressor
    range in diameter from 1-12 km (0.6-7        are neede d to se e this picture.
    mi); some have central pits typical of
    volcanic shields or cones.
    Bright Plains
   Located along the left central edge of
    the image is a cluster of volcanic
    domes that ranges from 1.5 km (1
    mi) to 7.5 km in diameter (5 mi).
    The domes and their deposits are
    located at the convergence of radar-
    bright lineaments that are
    interpreted to be faults and troughs.
    In some places the domes overlie the
    faults. The faults and troughs extend
    into the lower parts of the image
    where they terminate against dark                  QuickTime™ and a
    plains deposits and are crosscut at      TIFF (Un compressed) decompressor
    right angles by additional faults. The      are neede d to se e this picture.
    relationship between these features
    indicates that multiple episodes of
    faulting and volcanism have
    occurred.
     Ovda Regio
   The tectonic fabric of this region of
    Ovda Regio trends predominantly east-
    west. The large radar-dark areas are
    probably tectonically formed basins that
    have been filled in by fluid lava flows,
    thus presenting a smooth surface to the
    Magellan radar system.




                                                         QuickTime™ and a
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       Ridges and Troughs
   On this bright, lineated terrain Alpha
    Regio is a series of troughs, ridges,
    and faults running in every direction.
    The lengths of these features range
    from 10 km (6.3 mi) to 60 km (37
    mi). The elevation of Alpha Regio
    varies over a range of 4 km (2.5 mi).
    Low-lying areas appear dark in the
    radar images and may be filled with
    lava. Volcanoes appear as bright
    spots on the smooth plains. Notice
    the large volcano in the upper right.              QuickTime™ and a
    At the center of this 35 km (22 mi)      TIFF (Un compressed) decompressor
    volcano is a caldera; its western           are neede d to se e this picture.
    edge appears to be either a debris
    flow or a lava flow.
           Highlands
   Several tectonic events formed this complex
    terrain, which is part of the interior of Ovda
    Regio. An underlying fabric of ridges and
    valleys lies NE-SW. These ridges are spaced
    10-20 km (6-12 mi) apart and may have
    been caused by compression of the crust at
    right angles to the ridge. The ridges are cut
    by bright features extending NW-SE. The
    largest valleys, particularly the 20 km (12
    mi) wide valley extending across the image,
    were filled with dark material, probably
    lava. The complexity of Ovda Regio attests                 QuickTime™ and a
    to a long history of tectonic deformation.       TIFF (Un compressed) decompressor
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     Eastern Lakshmi
   Lava flows blanket the flat
    plains region of eastern
    Lakshmi. The dark flows most
    likely represent smooth flows
    similar to pahoehoe flows on
    Earth, while the brighter areas
    are rougher flows resembling
    Earth's aa flows. Three dark
    splotches mark the tops of
    these lava flows. Because of
    the thick atmosphere
    surrounding Venus, small                     QuickTime™ and a
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    impactors break up before they        are neede d to se e this picture.
    hit the surface. The fragments
    are deposited over the surface
    and produce the dark splotches
    seen here. Notice the splotch
    on the far right has a crater at
    its center, indicating that the
    impactor was not completely
    destroyed.
       Lava flows
   This mosaic highlights a system
    of east-trending, radar-bright
    and dark lava flows that collide
    with and breach a north-trending
    ridge belt (left of center). Upon
    breaching the ridge belt, the lava
    pooled, forming a radar-bright
    deposit approximately 100,000
    square km (right side of image).
    The source of the lava is the
    Corona Derceto, which lies about
    300 km (186 mi) west of the                    QuickTime™ and a
    scene.                               TIFF (Un compressed) decompressor
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      Coronas in Fortuna
   Two large oval features can be seen
    in this image of Fortuna. On the left
    is Ba'het Patera, 230 km (138 mi)
    long and 150 km (90 mi) across. A
    portion of Onatah Corona, over 350
    km (210 mi) in diameter, is visible on
    the right. Both features are
    surrounded by a ring of ridges and
    troughs. The central areas of the
    coronae contain radial fractures as
    well as volcanic domes and flows.
    Coronae may form due to the
    upwelling of hot material from deep                QuickTime™ and a
                                             TIFF (Un compressed) decompressor
    in the interior of Venus. These two         are neede d to se e this picture.
    coronae may have formed at the
    same time over a single upwelling.
          Arachnoids
   Named by the Soviets for their spider
    and cobweb-like appearance,
    arachnoids are one of the more
    remarkable features found on Venus.
    They are 50 to 230 km (30 to 138 mi)
    diameter circular structures, with a
    central volcanic feature surrounded by
    a complex network of fractures.
    Arachnoids are similar in form but
    generally smaller than coronae. The
    radar- bright lines extending for many
    kilometers beyond the arachnoids may               QuickTime™ and a
    have been caused by an upwelling of      TIFF (Un compressed) decompressor
                                                are neede d to se e this picture.
    magma from the interior of Venus,
    which pushed up the surface to form
    cracks.

				
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