Editing Caloris Planitia (section)

==Appearance==
[[File:MESSENGER first photo of unseen side of mercury cropped to Caloris.jpg|thumb|left|200px|''[[MESSENGER]]''{{'}}s first image of the unseen side of Mercury from a distance of about {{convert|27000|km|mi|-3}} cropped to highlight Caloris. The rim is hard to discern as the Sun is directly overhead, preventing shadows.]]

Caloris was discovered on images taken by the ''[[Mariner 10]]'' probe in 1974. Its name was suggested by [[Brian O'Leary]], astronaut and member of the ''Mariner 10'' imagery team.<ref name=Morrison_1976/> It was situated on the [[Terminator (solar)|terminator]]—the line dividing the daytime and nighttime hemispheres—at the time the probe passed by, and so half of the crater could not be imaged. Later, on January 15, 2008, one of the first photos of the planet taken by the ''[[MESSENGER]]'' probe revealed the crater in its entirety.

The basin was initially estimated to be about {{convert|810|mi|km|abbr=on}} in diameter, though this was increased to {{convert|960|mi|km|abbr=on}} based on subsequent images taken by ''MESSENGER''.<ref name="newscientist30012008"/> It is ringed by mountains up to {{convert|2|km|mi|abbr=on}} high.  Inside the crater walls, the floor of the crater is filled by lava plains,<ref name="becca">{{cite journal|last1=Thomas|first1=Rebecca J.|last2=Rothery|first2=David A.|last3=Conway|first3=Susan J.|last4=Anand|first4=Mahesh|title=Long-lived explosive volcanism on Mercury|journal=Geophysical Research Letters|date=16 September 2014|volume=41|issue=17|pages=6084–6092|doi=10.1002/2014GL061224|bibcode = 2014GeoRL..41.6084T |doi-access=free|url=https://hal-insu.archives-ouvertes.fr/insu-02276045/file/HAL_Thomas_et_al-2014-Geophysical_Research_Letters.pdf}}</ref> similar to the [[lunar mare|maria]] of the [[Moon]]. These plains are superposed by explosive vents associated with pyroclastic material.<ref name="becca"/> Outside the walls, material ejected in the impact which created the basin extends for {{convert|1,000|km|mi|abbr=on}}, and concentric rings surround the crater.

In the center of the basin is a region containing numerous radial troughs that appear to be [[extensional fault]]s, with an unrelated {{convert|40|km|mi|abbr=on}} crater, [[Apollodorus (crater)|Apollodorus]], located near the center of the pattern. The exact cause of this pattern of troughs is not currently known.<ref name="newscientist30012008"/> The feature is named [[Pantheon Fossae]].<ref>[http://messenger.jhuapl.edu/gallery/sciencePhotos/image.php?gallery_id=2&image_id=182 Mercury's First Fossae] {{webarchive|url=https://web.archive.org/web/20140714162830/http://messenger.jhuapl.edu/gallery/sciencePhotos/image.php?gallery_id=2&image_id=182 |date=2014-07-14 }}. ''[[MESSENGER]]''. May 5, 2008. Accessed on July 13, 2009.</ref>