section_path: Planetary geology
section_name: Planetary geology
paragraph_text: Planetary geology
  
  With the advent of space exploration in the twentieth century, geologists have begun to look at other planetary bodies in the same ways that have been developed to study the Earth. This new field of study is called planetary geology (sometimes known as astrogeology) and relies on known geological principles to study other bodies of the solar system. This is a major aspect of planetary science, and largely focuses on the terrestrial planets, icy moons, asteroids, comets, and meteorites. However, some planetary geophysicists study the giant planets and exoplanets.
  
  Although the Greek-language-origin prefix geo refers to Earth, "geology" is often used in conjunction with the names of other planetary bodies when describing their composition and internal processes: examples are "the geology of Mars " and " Lunar geology ". Specialized terms such as selenology (studies of the Moon), areology (of Mars), etc., are also in use.
  
  Although planetary geologists are interested in studying all aspects of other planets, a significant focus is to search for evidence of past or present life on other worlds. This has led to many missions whose primary or ancillary purpose is to examine planetary bodies for evidence of life. One of these is the Phoenix lander, which analyzed Martian polar soil for water, chemical, and mineralogical constituents related to biological processes.