Archive Astronomy Questions of the Week - International Year of Astronomy 2009
In which parts of the universe can life develop?
The habitable zone for stars of different sizes
Living organisms as we know them need water to survive. In order for there to be liquid water on the surface of a planet, it should not be too far from its central star, that is to say its "sun". Otherwise, the water will freeze. However, the planet should also not get too close to its source of light and heat - if it does, the precious liquid will evaporate.
A planet must lie within a certain distance range from the central star in order for water to exist in liquid form on its surface over a long period of time. This range is called the habitable zone or life zone. The precise boundaries of this life zone in a particular planetary system depend first and foremost on the size of its star. The figure shows where the habitable zone lies for stars of different sizes.
Galaxies have life zones
Habitable zones can also be indentified for galaxies, large conglomerations of stars and planetary systems. On the one hand, a planetary system cannot be too far from the centre of its galaxy. This is because the centre contains sufficient quantities of the chemical elements that are essential for the development of life forms. On the other hand, however, the habitable planetary system should lie at a certain minimum distance from the centre of the galaxy as well. Impacting asteroids and strong radiation would otherwise make it impossible for life to develop.
|Dr. Manfred Gaida
German Aerospace Center
Space Administration, Space Science
Tel.: +49 228 447-417
Fax: +49 228 447-745