Steven Dutch, Natural and Applied Sciences,
University of Wisconsin - Green Bay
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|Because of its rotational resonance, Mercury has two "hot poles" where the sun shines straight down when Mercury is closest to the Sun. This radio map shows them clearly.|
|A Mariner 10 mosaic of Mercury|
The Caloris Basin
The Caloris Basin was on the terminator as seen by Mariner 10. Only about
a third of it is visible. If the above two images look like photos cut out
and stitched together, that's because in 1974 "cut and paste" literally
referred to scissors and Elmer's Glue. At left is a more modern computer
The Caloris Basin is a huge multiple ring impact basin. The name, from
the Latin for "heat" is due to the basin peing at one of the three hot poles
of Mercury. This is one of the places the sun can be overhead when Mercury
is at perihelion.
||Directly opposite the Caloris basin is the chaotic
terrain, a jumble of hills and valleys. Many planetary geologists
suspect the shock from the Caloris impact was focused by Mercury's large
core and fractured the crust on the other side of the planet. Note the
smooth floor of one crater from lava that clearly post-dates the chaotic
||Detail of chaotic terrain.
||The numerous scarps on Mercury seem to be thrust faults and
suggest the radius of the planet has decreased by a few kilometers,
possibly from cooling and shrinkage of its core
Most of Mercury has fairly wide plains between craters. These intercrater plains indicate that Mercury was resurfaced after most of its early impact bombardment, probably by volcanism.
The Snowball in Hell
One of the longest standing items on the planetary exploration to-do list was
accomplished in January, 2008 when the MESSENGER mission arrived at Mercury
after a 34 year absence. The
mission plans to use multiple gravity assists before settling into orbit around
Mercury and mapping the entire planet in 2011.
||In this false-color image, different surface materials show up in
blue or orange. The Caloris Basin is the huge orange oval. The bright
orange patches around the edge are thought to be volcanic vents.
||Intercrater planes and flat-bottomed craters.
||Highly detailed look at a crater rim. This area is at the lower
right corner of the view below.
||Intercrater plains, a scarp, and a nearly flooded peak ring crater.
||This crater surrounded by radiating cracks has been dubbed "the
spider." Could it be the result of fracturing the solid surface of a
still hot impact melt or thick lava flow?
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Created 6 April 1999, Last Update
14 December 2009
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