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Caloris Planitia
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<p>Caloris Planitia /kəˈlɔːrɪs pləˈnɪʃ(i)ə/ is a <a href="/facts/Planitia/yM1ghtmc">plain</a> within a large <a href="/facts/Impact_basin/nWntooh4">impact basin</a> on <a href="/facts/Mercury_(planet)/lVa1GIyX">Mercury</a>, informally named Caloris, about 1,550 km (960 mi) in <a href="/facts/Diameter/6uNn4VmU">diameter</a>. It is one of the <a href="/facts/List_of_largest_craters_in_the_Solar_System/sUBmmIrv">largest impact basins in the Solar System</a>. "Calor" is <a href="/facts/Latin/pM3Kge85">Latin</a> for "<a href="/facts/Heat/FjDGssCs">heat</a>" and the basin is so-named because the <a href="/facts/Sun/CadPCVHh">Sun</a> is almost directly overhead every second time Mercury passes <a href="/facts/Perihelion/VaL6ow9w">perihelion</a>. The crater, discovered in 1974, is surrounded by the <a href="/facts/Caloris_Montes/PSswh0cP">Caloris Montes</a>, a ring of <a href="/facts/Mountain/wboT5GJc">mountains</a> approximately 2 km (1.2 mi) tall. </p>