The Caloris impact
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Transcript of The Caloris impact
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The Caloris impactBy Antonio SolazziBased on the article:
Stratigraphy of the Caloris Basin, Mercury by McCauley et al
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General Information
• The Caloris basin is approximately 1500m in diameter.
• It consists of 3-6 rings of mountains, a large impact basin and associated terrain features.
• Also of note are secondary impact craters caused by debris from the main impact.
• Until recently, only part of the impact basin had been imaged by Mariner 10.
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New information
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Features of the Basin
• The Caloris impact and associated effects generated many different types of terrain features on Mercury which can be divided into four groups:
• Caloris Montes Formations• Nervo Formations• Odin Formations• Van Eyck Formations
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Caloris Montes Formations
• This type of terrain is most commonly found on the outer edges of the Caloris basin.
• The outer rim of the basin is made up almost entirely of this type of terrain.
• This terrain consists of “a jumbled array of smooth-surfaced but highly segmented rectilinear mountain massifs that rise several kilometers above the surrounding terrain.”
• Individual section are usually 30 to 50 km long.
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An example of Caloris Montes formations
•The large arrow highlights the Montes formation.
•The Montes formation makes a visible outer edge to the basin.
•Thought to be made up of ejecta from Caloris combined with uplifted and fractured pre-basin bedrock.
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Nervo Formations
• Nervo formations consist of “rolling to locally hummocky plains that lie in inter-massif depressions.”
• This type of terrain is generally found inside the Caloris basin.
• It is sometimes referred to as inter-montane plains.
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An example of Nervo formations
•These formations are thought to be caused by fallback ejecta.
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Odin Formations
• These formations are closely spaced, smooth hills that are about 1km across.
• They generally occur within 600m to 800m of the Caloris basin.
• They are though to be made up of blocky, high angle, late-arriving eject from the Caloris impact that has been partially covered.
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An example of an Odin formation
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Van Eyck Formations
• This terrain is made up of radial ridges and grooves along with locally swirly terrain and is extensively embayed by smooth plains.
• This terrain is made up of “ballistically emplaced ejecta mixed with prebasin bedrock.”
• It also includes several areas of craters that are interpreted as being Caloris secondaries formed by far-flung ejecta.
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An example of Van Eyck Formations
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Relative dating of craters using Caloris
• In order to relatively date the Caloris impact a crater record must be established.
• One way of doing this is using a 5 point scale where C1 are the oldest craters and C5 the newest.
• Using this system the Caloris impact is relatively dated to the period to the late C3 time period.
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C1 and C2 craters
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C3 and C4 craters
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C5 Crater
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Hilly and lineated terrain
• On the other side of Mercury from the Caloris basin terrain exists that is very different from other terrain on Mercury.
• This terrain consists of hills 5km to 10km wide and 2km deep along with valleys up to 15km wide and 120km long.
• This terrain is thought to have been caused by the shock wave from the Caloris impact propagating through the core of Mercury.
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Hilly and lineated terrain
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The spider
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Conclusions
• The Caloris impact was a major event that left marks over a large section of Mercury’s surface.
• Some of the features of the Caloris impact can be used to relatively date different craters and features on the planet.