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Caloris Basin

2007 Schools Wikipedia Selection. Related subjects: Space (Astronomy)

   The Caloris Basin: The above is a mosaic of half of the spectacular
   Caloris Basin on Mercury, photographed by NASA's Mariner 10 spacecraft
   in 1974-75. The other half has never been photographed.
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   The Caloris Basin: The above is a mosaic of half of the spectacular
   Caloris Basin on Mercury, photographed by NASA's Mariner 10 spacecraft
   in 1974-75. The other half has never been photographed.

   The Caloris Basin, also called Caloris Planitia, is an impact crater on
   Mercury about 1350km in diameter, one of the largest impact basins in
   the solar system. Caloris is Latin for heat and the basin is so-named
   because the Sun is almost directly overhead every second time Mercury
   passes perihelion. The crater is surrounded by a ring of mountains
   about two kilometers tall.

Appearance

   The Caloris Basin was discovered on images taken by the Mariner 10
   probe in 1974. It was situated on the terminator - the line dividing
   the daytime and nighttime hemispheres - at the time the probe passed
   by, and so half the crater has never been imaged.

   The crater is about 1300km (810 miles) in diameter, and is ringed by
   mountains up to 2km high. Inside the crater walls, the floor of the
   crater is filled by lava plains, similar to the maria of the Moon.
   Outside the walls, material ejected in the impact which created the
   basin extends for 1000 km, and concentric rings surround the crater.

Formation

   Bodies in the inner solar system experienced a heavy bombardment of
   large rocky bodies in the first billion years or so of the solar
   system. The impact which created the Caloris basin must have occurred
   after most of the heavy bombardment had finished, because fewer impact
   craters are seen on its floor than exist on comparably-sized regions
   outside the crater. Similar impact basins on the Moon such as the Mare
   Imbrium and Mare Orientale are believed to have formed at about the
   same time, possibly indicating that there was a 'spike' of large
   impacts towards the end of the heavy bombardment phase of the early
   solar system

Global effects

   The giant impact believed to have formed Caloris may have had
   consequences for the whole planet. At the exact antipode of the basin
   is a large area of hilly, grooved terrain, known as the 'Weird
   Terrain', which is thought by some to have been created as seismic
   waves from the impact converged on the opposite side of the planet .
   This hypothetical impact is also believed to have triggered volcanic
   activity on Mercury, resulting in the formation of smooth plains .

Emissions of gas

   Mercury has a very tenuous and transient atmosphere, containing small
   amounts of hydrogen and helium captured from the solar wind, as well as
   heavier elements such as sodium and potassium. These are thought to
   originate within the planet, being 'out-gassed' from beneath its crust.
   The Caloris Basin has been found to be a significant source of sodium
   and potassium, indicating that the fractures created by the impact
   facilitate the release of gases from within the planet. The Weird
   Terrain is also a source of these gases. .
   Retrieved from " http://en.wikipedia.org/wiki/Caloris_Basin"
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