Mars. All are rocky bodies covered by a thin layer of atmosphere. Even the EarthΓÇÖs relatively thick atmosphere is only a narrow outer ΓÇ£peelΓÇ¥ about 150 to 200 kilometers deep atop a rocky core nearly 12,800 kilometers in diameter. The planetΓÇÖs atmosphere differs from the other rocky planets in the abundance of water, nitrogen, and oxygen, which has shaped its surface in unique ways. Wind and rain have sculpted the EarthΓÇÖs exterior over billions of years, relentlessly wearing down mountain ranges, filling depres- sions, and carving even the hardest rocks to create a rich and intricate panoply of formations. Impact craters, the evidence of planetary birth so evident on nearly atmosphereless Mercury,
