Conference publications


XIV conference

Life in Extrasolar Planetary Systems: the Search for a Second Earth

Franck A.S., Bounama C., von Bloh W.

A. S. Franck, Potsdam Institut for Climate Impact Research, P.O. Box 601203, 14412 Potsdam, Germany

1 pp.

Is there life beyond planet Earth? This is one of the grand enigmas

which humankind tries to solve through scientific research. Recent

progress in astronomical measurement techniques has confirmed the

existence of a multitude of extra-solar planets. On the other hand,

enormous efforts are being made to assess the possibility of life on

Mars. All these activities have stimulated several investigations about

the habitability of cosmic bodies. The habitable zone (HZ) around a

given central star is defined as the region within which an Earth-like

planet might enjoy the moderate surface temperatures required for

advanced life forms. At present, there are several models determining

the HZ. One class of models utilises climate constraints for the

existence of liquid water on a planetary surface. Another approach is

based on an integrated Earth system analysis that relates the boundaries

of the HZ to the limits of photosynthetic processes. Within the latter

approach, the evolution of the HZ for our solar system over geological

time scales is calculated straightforwardly, and a convenient filter can

be constructed that picks the candidates for photosynthesis-based life

from all the extra-solar planets discovered by novel observational

methods. These results can then be used to determine the average number

of planets per planetary system that are within the HZ. With the help of

a segment of the Drake equation, the number of "Gaias" (i.e. extra-solar

terrestrial planets with a globally acting biosphere) is estimated. This

leads to the thoroughly educated guess that there should exist half a

million Gaias in the Milky Way.

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