Mercury Images

Steven Dutch, Professor Emeritus, Natural and Applied Sciences, University of Wisconsin - Green Bay

General Views

	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 processed mosaic.

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.

Chaotic Terrain>

	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 terrain.
	Detail of chaotic terrain.

Scarps

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

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Intercrater Plains

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

	Radar images of Mercury reveal a bright reflection at the poles, matching the radar signature of ice. The sun's powerful tidal effects keep Mercury's equator locked on the sun and ensure that the poles never receive more than grazing illumination. Deep craters never get sunlight at all.
	Left: both poles show reflections. Bottom: detailed maps show the reflections match craters exactly once a slight correction to Mercury's poles is applied (red asterisk shows the revised pole locations). Some researchers suggest that sulfur compounds rather than ice could produce the echoes.

We're Ba-a-a-ack

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 11 January 2020