Flamsteed Astronomy Society

Habitable Zones beyond the Solar System

by Dr Martin Heath, April 2, 2007

Dr Martin Heath of Greenwich Community College talked about ‘Habitable Zones beyond the Solar System — recent discoveries of other planetary systems’.  Martin has published on the habitable zones of Red Dwarf stars.  He began by exploring the circumstances and development of life on Earth.  He focused on the development of the Earth’s ecosystem with particular emphasis on the role of forests in the evolution of complex life forms on Earth including the uses of wood by Man.   He then turned back to look at the ‘bigger scale’ — the factors that contributed to producing a ‘Habitable Zone’ containing Earth’s orbit in the solar system.  Martin contrasted Earth circumstances with the Moon, Mars and Venus:  so near to habitability, and yet so far.

Many factors in the formation of the solar system have influenced Earth’s habitability and the suitability (or lack of) in Earth’s near neighbours.   Distance from the Sun, size, composition, orbital parameters, are all key.  The influence of the Moon, relatively an extraordinarily large satellite which stabilises the Earth’s spin has been crucial.  The way the giant planets formed, moved orbits, and ‘cleaned up’ the solar system has also been critical.  Martin looked at how such factors might be repeated or vary in extrasolar systems elsewhere in the Universe.   He explored how different types of star might be more or less favourable for habitable zones.

Dr Martin Heath (pic: Mike Dryland)

To close, Martin returned to the interrelationship of the parts of Earth’s ecosystem.  The development of complex life on Earth has not just required the solar system dynamics that created a habitable planet, but has also depended on the way life itself evolved and shaped the ecosphere.  Man is now the primary influence in that development.  Over the last few decades human activities have created changes at rates far beyond those measured in the planet’s history up to now.  The paramount example is the presence of greenhouse gases in the atmosphere and their controversial effect on climate change.  It may be that the conditions for the creation and development of life are very common in the Universe.  The miracle on Earth is that life has evaded extinction for so long.   But for how much longer?



Martin looked at stellar evolution and how a star may support a habitable zone at a certain point in its life cycle.  Many kinds of star may provide habitable zones.  Red dwarves should do so and this kind of star is very common.  Planets have even been detected in binary star systems and might be habitable.  There may indeed exist a ‘Tatooine’ with double suns.  Around 218 extrasolar planets have now been detected (Apr 2007).

A range of theoretical habitable zones with stars of different mass (our solar system at centre).  Wikipedia

pic: Mike Dryland

pic: Mike Dryland