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Physics LibreTexts

7: The Rocky Planets

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“How inappropriate to call this planet Earth when clearly it is Ocean…” - Arthur C. Clark, 1917-2008

Learning Objectives

Upon completion of this module, the student will be able to:Upon completion of this module, the student will be able to:

  • Identify the characteristics of Rocky Planets
  • Define craters and cratering
  • Identify the primary characteristics of each rocky planet
  • Identify the similar characteristics of each rocky planet
  • Describe a circumstellar habitable zone
  • Discuss the characteristics of the Moon, Deimos, and Phobos

  • 7.1: What do you think?
    This page discusses the rocky planets of the Solar System—Mercury, Venus, Earth, and Mars—highlighting their shared visual traits like solid surfaces and terrain features. While initially appearing barren, these planets each have distinct colors and atmospheric conditions: Mercury is grayish, Venus has a thick yellowish atmosphere, Earth is vibrant with blues and greens, and Mars is red from iron oxide.
  • 7.2: Comparing Planets
    This page presents an overview of Comparative Planetology, contrasting Rocky planets (Mercury, Venus, Earth, Mars) with Gas Giants (Jupiter, Saturn, Uranus, Neptune). It highlights key differences: Rocky planets are smaller, solid, cratered, and closer to the Sun, while Gas Giants are larger, gaseous, with rings and moons, and located farther away with longer revolution periods and atmospheric water.
  • 7.3: Rocky Planets
    This page discusses rocky planets, or terrestrial planets, which are smaller than gas giants and many exoplanets. They feature solid surfaces with craters, few or no moons, and no rings. Additionally, these planets may exhibit signs of past or present tectonic and volcanic activity.
  • 7.4: Craters
    This page discusses craters, which are bowl-shaped depressions created mainly by impacts from space debris like asteroids and comets, though volcanic activity can also contribute. Crater sizes vary widely, and some impacts produce ray features that appear like splashes around the site.
  • 7.5: Planet Mercury
    This page provides an overview of Mercury, highlighting it as the smallest and closest planet to the Sun, with no significant atmosphere, extreme temperature fluctuations, and a cratered surface similar to the Moon's. It mentions Mercury's inactive geological features, presence of water and ice in polar regions, and absence of erosion, dunes, polar caps, and natural satellites, while the potential for life is still uncertain.
  • 7.6: Planet Venus
    This page describes Venus as Earth's twin, highlighting its similar size and atmosphere. It is the closest planet to Earth and the second brightest in the night sky, known as the Morning and Evening Star. Key features include numerous craters, over 1,600 volcanoes, a dense carbon dioxide atmosphere, high pressure, lack of water and polar caps, erosion, dunes, and no known life or satellites.
  • 7.7: Planet Earth
    This page discusses Earth as the largest rocky planet in the Solar System, unique for its liquid water covering 75% of its surface. Key influences on Earth include the Moon and Sun's gravitational pull on tides, while geological processes like erosion and volcanism shape its landscape.
  • 7.8: Earth’s Moon
    This page discusses the Earth-Moon system as a double planet, highlighting the Moon's significant size relative to Earth. It notes the Moon's extreme temperature variations and explains the Giant Impact Theory, which proposes the Moon's formation from a collision with a Mars-sized body. Furthermore, it mentions the discovery of water ice in the Moon's polar craters, estimating that the upper lunar layer holds about 32 ounces of water per ton.
  • 7.9: Planet Mars
    This page discusses Mars, highlighting its status as the fourth planet from the Sun, its polar caps, and water in solid form. It notes Mars' history of volcanic activity and extensive exploration by spacecraft. The North Polar Cap is primarily water ice and varies with seasons, while the South Polar Cap is made of carbon dioxide ice, remaining constant and smaller. These contrasting characteristics are attributed to differing polar climates, similar to those on Earth.
  • 7.10: Snow on Mars
    This page discusses the Phoenix Mars Lander's 2009 observation of snow on Mars, which vaporized before reaching the ground. It highlights the discovery of water and ice beneath the surface, as well as prominent Mars features such as impact craters, inactive volcanoes, and a carbon dioxide-rich atmosphere. Mars also has liquid and ice water, erosion, dunes, and two moons, Deimos and Phobos. The search for extraterrestrial life on Mars continues.
  • 7.11: A Martian Controversy
    In the late 1800s, astronomer Percival Lowell founded an observatory in Flagstaff, Arizona, where he advocated the existence of Martian canals, claiming they indicated intelligent life. His ideas, influenced by earlier observations and popularized by H.G. Wells, stirred public fascination and debate. However, subsequent spacecraft missions like Mariner 4 disproved the existence of these canals, indicating Lowell's observations were based on optical illusions.
  • 7.12: Martian Moons
    This page discusses Mars' two small moons, Deimos and Phobos, named after the Greek words for Dread and Fear. Discovered in 1877, Phobos is larger, measuring over 16 miles wide and has a rapid orbit of 11 hours and 6 minutes around Mars. Both moons are irregularly shaped, thought to be captured asteroids or remnants from a collision with Mars, and are characterized by craters and lack of atmosphere.
  • 7.13: Characteristics of the Solar System’s Rocky Planets
    This page compares the rocky planets of our solar system: Mercury has impact craters and lacks atmosphere; Venus has extreme volcanic activity and a dense CO2 atmosphere; Earth is noted for its water and life; Mars features large craters and potential subsurface water. Deimos and Phobos, the moons of Mars, are small, cratered, and without atmosphere. Additionally, there is a mnemonic included for remembering the planets.


This page titled 7: The Rocky Planets is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by Lumen Learning via source content that was edited to the style and standards of the LibreTexts platform.

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