Feature
17 Sep 2009

New ‘Drake equation’ for alien habitats

An equation that counts habitats suitable for alien life could complement the Drake equation, which estimates the probability of finding intelligent beings elsewhere in the galaxy. Heather Catchpole reports.

Credit: Getty Images

SYDNEY: A mathematical equation that counts habitats suitable for alien life could complement the Drake equation, which estimates the probability of finding intelligent alien beings elsewhere in the galaxy.

That equation, developed in 1960 by U.S. astronomer Frank Drake, estimates the probability of intelligent life existing elsewhere in our galaxy by considering the number of stars with planets that could support life (see “Are we alone?“).

The new equation, under development by planetary scientists at the Open University in Milton Keynes, England, aims to develop a single index for habitability based on the presence of energy, solvents such as water, raw materials like carbon and whether or not there are benign environmental conditions.

 

Input of energy

The draft equation will be presented today at the European Planetary Science Congress in Potsdam, Germany, to garner feedback.

“At present, there is no easy way of directly comparing the suitability of different environments as a habitat for life,” said planetary scientist Alex Hagermann, who led the research.

Currently, the experts are focussing on energy, which, in the form of visible and infrared light is important for photosynthesis, but can also come in forms that can harm life, such as UV light and X-rays.

“If you can imagine a planet with a thin atmosphere that lets through some of this harmful radiation, there must be a certain depth in the soil where the ‘bad’ radiation has been absorbed but the ‘good’ radiation can penetrate,” said Hagermann.

 

Icy planetesimals

“We are looking to be able to define this optimal habitable region in a way that we can say that it is ‘as habitable’ or ‘less habitable’ than a desert in Morocco, for example,” he said.

So far there has been some criticism of the approach. Astrobiologist and physicist Paul Davies, of the University of Arizona in Tuscon, said it was a “pointless exercise” as the equation refers only to life as we know it.

“The main thing omitted from the conventional Drake equation is the possibility of life inside icy planetesimals, most of which are rogue objects, untethered to stars. Such life is, however, most unlikely to be intelligent,” he said.

Australian astrobiologist Malcolm Walter, with the University of New South Wales in Sydney, said in his opinion it was more important to focus on searching for Earth-like planets in other solar systems.

“The Drake equation is interesting in that it was Drake’s view of how to get started in thinking about the possibility of industrialised civilisations in the rest of the universe,” said Walter. “Going beyond that isn’t particularly useful because there are so many uncertainties in the basic Drake equation itself.”

Hagermann argued that it was important to approach the search for alien life from a theoretical as well as an experimental viewpoint, and that despite uncertainties about what sort of environment aliens might require, there were some things such as energy that are crucial to life.

“In one way or another, this is what our thinking with regard to habitability is like: constrained by our limited experience of “life as we know it”. In our framework we would like to be able to question those assumptions,” he said.