Habitable Zone - Criticism

Criticism

  • The concept of a habitable zone is criticized by Ian Stewart and Jack Cohen in their book Evolving the Alien, for two reasons: the first is that the hypothesis assumes alien life has the same requirements as terrestrial life; the second is that, even assuming this, other circumstances may result in suitable planets outside the "habitable zone". For instance, Jupiter's moon Europa is thought to have a subsurface ocean with an environment similar to the deep oceans of Earth. The existence of extremophiles (such as the tardigrades) on Earth makes life on Europa seem more plausible, despite the fact that Europa is not in the presumed CHZ. Astronomer Carl Sagan believed that life was also possible on the gas giants, such as Jupiter itself. A discovery of any form of life in such an environment would expose these hypothetical restrictions as too conservative. Life can evolve to tolerate extreme conditions when the relevant selection pressures dictate, and thus it is not necessary for them to be "just right".
  • Differing levels of volcanic activity, lunar effects, planetary mass, and even radioactive decay may affect the radiation and heat levels acting on a planet to modify conditions supporting life. And while it is likely that Earth life could adapt to an environment like Europa's, it is far less likely for life to develop there in the first place, or to move there and adapt without advanced technology. Therefore, a planet that has moved away from a habitable zone is more likely to have life than one that has moved into it.
  • Just as different levels of atmospheric pressure can affect water remaining in liquid state, the presence of dissolved compounds, such as salts or ammonia (a powerful antifreeze) can lower the freezing point of water. Earth's oceans are saline, which helps prevent them freezing. Greenhouse effects, solvents in water or a combination of these factors could potentially enable planets with certain conditions to sustain surface water. For example, briny water is proposed as an explanation for Seasonal flows on warm Martian slopes.

Read more about this topic:  Habitable Zone

Famous quotes containing the word criticism:

    A bad short story or novel or poem leaves one comparatively calm because it does not exist, unless it gets a fake prestige through being mistaken for good work. It is essentially negative, it is something that has not come through. But over bad criticism one has a sense of real calamity.
    Rebecca West (1892–1983)

    Good criticism is very rare and always precious.
    Ralph Waldo Emerson (1803–1882)

    I am opposed to writing about the private lives of living authors and psychoanalyzing them while they are alive. Criticism is getting all mixed up with a combination of the Junior F.B.I.- men, discards from Freud and Jung and a sort of Columnist peep- hole and missing laundry list school.... Every young English professor sees gold in them dirty sheets now. Imagine what they can do with the soiled sheets of four legal beds by the same writer and you can see why their tongues are slavering.
    Ernest Hemingway (1899–1961)