text: One should not assume that a carbonate-silicate cycle would appear on all terrestrial planets. To begin, the carbonate-silicate cycle requires the presence of a water cycle. It therefore breaks down at the inner edge of the Solar System's habitable zone. Even if a planet starts out with liquid water on the surface, if it becomes too warm, it will undergo a runaway greenhouse, losing surface water. Without the requisite rainwater, no weathering will occur to produce carbonic acid from gaseous CO. Furthermore, at the outer edge, CO may condense, consequently reducing the greenhouse effect and reducing the surface temperature. As a result, the atmosphere would collapse into polar caps.
  Mars is such a planet. Located at the edge of the solar systems habitable zone, its surface is too cold for liquid water to form without a greenhouse effect. With its thin atmosphere, Mars mean surface temperature is . In attempting to explain topographical features resembling fluvial channels, despite seemingly insufficient incoming solar radiation, some have suggested that a cycle similar to Earth's carbonate-silicate cycle could have existed – similar to a retreat from Snowball Earth periods. It has been shown using modeling studies that gaseous CO and HO acting as greenhouse gases could not have kept Mars warm during its early history when the Sun was fainter because CO would condense out into clouds. Even though CO clouds do not reflect in the same way that water clouds do on Earth, it could not have had much of a carbonate-silicate cycle in the past.
  By contrast, Venus is located at the inner edge of the habitable zone and has a mean surface temperature of . After losing its water by photodissociation and hydrogen escape, Venus stopped removing carbon dioxide from its atmosphere, and began instead to build it up, and experience a runaway greenhouse effect.
  On tidally locked exoplanets, the location of the substellar point will dictate the release of carbon dioxide from the lithosphere.