Is the Earth habitable?

Long been considered: our planet is so close to the sun, even to a 10% greater — and the end of life. A new estimate makes the prospect of even more joyful: the earthly life of sunsets over the horizon in the next few hundred million years.

Researchers from the University of Pennsylvania (USA) expressed the need for revision of the habitable zone as a concept and offered his own version, based on more precise, in their opinion, taking into account the influence of greenhouse gases on the planetary temperature.

Scientists have relied on models and Evan James Casting Pu. But the results were the original, the: habitable zone is actually farther from the star than previously thought, and her heavenly body closest to the border, therefore, also be removed. The calculations for the solar system, for example, just brought surprising results: it turns out, the earth barely fit for habitation, and habitable planets may extend to the orbit of Mars.

According to the new model (and contrary to the previous one), Kepler-22b and-667Ss Gliese lie outside the zone of habitability (highlighted in green). And Earth critically close to the same. (Here and below illustrate Chester Herman.)

How so? Lead author of Kopparapu Ravi Kumar (Ravi Kumar Kopparapu) reports that his team used the last time the database on the absorption of solar radiation by greenhouse gases (HITRAN and HITEMP). They are the parameters for water and carbon dioxide and exceed specified values previously available. Using the same model of the casting, which is the basis of modern mainstream assessments, the researchers would inevitably have a different meaning for the habitable zone exoplanets. Which is what happened.

The result is obvious: many considered habitable planets in practice far from places where there may be life.

We can already anticipate the puzzled questions astronomical community. First, in the early calculations, without the high absorbance values for water and carbon dioxide, the Earth was at the edge of the habitable zone, with its inner side. Even then, these estimates caused some distrust: So, whether our planet is only in 0.9 as well. AU from the Sun, its habitability would be disappointingly low, more precisely — there would be no. Under the new model is, the gap is even smaller. Consider, for example, the calculator habitable zone, lined by the authors online. Thus, the disadvantages of a percent of the distance to the sun — and the Earth would be dead?

Second (and this is even more important reason for the criticism), the amount of carbon dioxide in the world only three or four hundred million years ago, it was several times higher than the current one. Yes, the luminosity of the Sun was smaller — but just on the interest that can be counted on the fingers of one hand. Finally, 40 million years ago, ice sheets in Antarctica (located approximately at the same place and still is) not at all. However, only 30 million years ago, ice covered the continent, and brought it into a modern look — and all because of the fall in carbon dioxide in the atmosphere. It turns out that before the glaciation of Antarctica (and earlier, in the Carboniferous period), according to new calculations, the planet has been at least partially located outside the zone of habitability?

Note that the calculator on the atmospheric pressure on the planet's surface (affecting the greenhouse effect), as well as its size, and the resulting geothermal heat (very high at the "super-Earths"), does not affect the habitability, which is not very clear. Again, even when the solar luminosity in 1.015 from the present (such it will be in 200 million years) calculator finds the loss of land water shell. Is our life so vulnerable?

Furthermore, the model does not account for the influence of clouds, scattering into space solar radiation increases the albedo of the Earth. If at this point we do not know in detail the feedback mechanisms between the growth temperature and the formation of clouds, how can we talk about understanding the inner edge of the zone of habitability? If we believe a number of recent studies, it appears that the waste products of many plants and microbes can play in the formation of clouds, the same role as all other factors combined. If so, how do can determine the exact boundaries of the zone of habitability without complete information about microbes and plants for many light years away from us?

Study report is accepted for publication in the Astrophysical Journal, and with his preprint is available here.

Prepared according to the University of Pennsylvania.

Category: Science

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