Defintivno smo sami...
http://intelligentreasoning.bl...2006/05/privileged-planet.html
Stars:
Total number estimated in the Milky Way- 100 billion
Over 80% are low-mass red dwarfs (most likely lack a habitable zone)
1-2% are massive short-lived blue giants
Only about 4% of the stars are early G-type, main-sequence stars like our Sun
50% of those are in binary systems
Then we have to consider what % of those are in the Galactic Habitable Zone
Earth-like planets:
We now know that our solar system is not typical
We do know other planets exist
At least 4% of Sun-like stars have giant planets at least as massive as Jupiter.
Then we have the factors required for a planet to host complex life-
Summary:
Within the Galactic Habitable Zone
Within the Circumstellar Habitable Zone
Liquid water
Orbit a Spectral type G2 dwarf main sequence star
Protected by gas giants
Nearly circular orbit-
Oxygen rich
Correct mass
Large moon to stabilize the angle of rotation
Moderate rate of rotation
Terrestrial planet
Ratio of water to continents
Plate tectonic re-cycling
Magnetic field
Both plate tectonics and the magnetic field require the core have enough heat to keep it liquid. The convection currents mix the minerals before recycling and also produce the required magnetic field as it flows around the iron inner core.
The Earth’s orbit is slightly elliptical. When the Earth is closest to the Sun (perigee) the southern hemisphere is enjoying summer, i.e. the Earth’s axis of rotation has the southern hemisphere at a better angle (than the northern hemisphere) towards the Sun for absorbing its vital rays. The Earth has the bulk of its continents in the northern hemisphere. Water stores the heat and then transfers it around the globe.