Tidal Effects Change ‘Habitable Zone’ Concept
The existence of planets outside our solar system has been known since a long time. Scientists while searching life on these planets focused more on those which were in the habitable zone i.e. at a particular distance from their star, like sun in our solar system. Thus trying to ensure that water was present in liquid state in these planets, one of the main criteria for life’s existence. Two factors were said to be important for determining temperature in a planet; the distance from the energy source, the central star and the atmosphere on the planet. But Heller and his colleagues have researched that even tides can affect such planets and determine the habitability of them.
Heller’s research has been concluded from three facts. Firstly, tides change the axis of a planet’s rotation to become perpendicular to its orbit in a period of a few million years. Earth’s own axis of rotation is inclined at an angle of 23.5 degrees which in turn causes our seasonal changes. Earlier the planets which were categorized as habitable earlier now become unsuitable considering these effects. They would not be having any seasonal variations i.e. the poles will be extremely cold and the equators hot enough to evaporate any atmosphere leading to violent storms and winds.
The second effect would be to heat the planet, similar to the moon of Jupiter which constantly encounters volcanism.
Finally, tides synchronize earth’s rotation with the earth’s revolution thus synchronizing a day to fit into an year. This set-up is identical to the Earth and Moon. The moon only shows one of its face to Earth, the other face called as the “dark side of the moon”. As a result, one face of the Moon is hot with extreme radiation and the other face is freezing in eternal darkness. Heller’s research has raised doubts about the habitability of Earth like extra-solar planets which should be re-examined for tidal effects. They have applied their theory to one such planet; Gl581 g which was recently declared habitable. Heller’s studies says that since Gl581 g has no seasonal variations, probably there isn’t any water present on this planet, concluding with the statement that considering tidal effects, the chances of finding a habitable planet is weak and for finding a second Earth, a second sun should be sought.