The evolution of Venus: first too fast, then too slow

Scientists analysing the data from the European Venus Express spacecraft now orbiting Earth's prodigal twin planet have been piecing together an understanding of why the climate on both worlds is so different. Professor Fred Taylor of Oxford University will present the scenario in a talk at the RAS National Astronomy Meeting in Belfast on Wednesday 2nd April.

In the early stages of the Solar System, Venus seems to have evolved very rapidly compared to the Earth. Data from Venus Express supports the theory that the Earth's twin once had significant volume of water covering the surface but it appears that these oceans were lost in a very short geological timescale. As a result of the loss of water, the geological evolution of the surface of Venus slowed right down because it was unable to develop plate tectonics like the Earth. Biological evolution was prevented altogether. Thus, in terms of Venus being another Earth in climate and habitability terms, it evolved too quickly at first, then too slowly.

'They may have started out looking very much the same,' said Professor Taylor, 'but increasingly we have evidence that Venus lost most of its water and Earth lost most of its atmospheric carbon dioxide.'

Here, the CO2 is locked up in minerals in the crust, in the oceans, and in plant life. The release of some of this back into the atmosphere is the source of current concern about global warming and climate change. On Venus, most of the CO2 is still in the atmosphere and the surface temperature is a scorching 450 degrees Celsius, slowing or stopping geological as well as biological evolution. It is much too hot for life as we know it, for instance.

'The interesting thing is that the physics is the same in both cases' said Prof. Taylor. 'The great achievement of Venus Express is that it is putting the climatic behaviour of both planets into a common framework of understanding.'

The job is not finished yet - Venus Express is currently due to operate until May 2009, and the scientists involved are busy applying for an extension until 2011.

'We have plans for joint operations with the Japanese spacecraft called Venus Climate Orbiter that will arrive in December 2010,' said Taylor. 'Together, we can do things neither could do alone to crack some of the remaining puzzles about Venus.'