Understanding Earth's fiery twin

It has long been recognised that Earth and Venus share certain characteristics but results from the European Space Agency's (ESA) Venus Express spacecraft, published in Nature (29th November 2007), reveal more detail about the processes at work that have made Venus evolve so differently to Earth.

Venus Express, which was launched in November 2005, has been providing data on Earth's fiery cousin since arriving in Venus's orbit in April 2006. The latest findings appear in a special section of the 29th November issue of Nature containing nine individual papers devoted to Venus Express science activities - providing the most detailed picture of the planet to date.
Ian Pearson, Minister for Science and Innovation, said: "These latest results from Venus Express are providing a real insight into the extreme climatic processes at work on a planet that is very similar to our own. Understanding the influencing factors of global warming on Venus could help us in mitigating the threat here on Earth. British scientists and engineers are also playing a leading role in this very important European mission, thereby further demonstrating both the contribution, and the continuing strength, of the UK space industry."

Speaking at an ESA Press Conference in Paris today Professor Fred Taylor from the University of Oxford, interdisciplinary scientist on the mission and co-investigator on the VIRTIS instrument, said, "It is now becoming clearer why the climate on Venus is so very different from that on Earth, despite the planets themselves being very similar in many ways. There are many common processes at work, such as a carbon dioxide driven greenhouse effect, volcanic activity, and atmospheric erosion by solar particles and radiation. On Venus, these have worked to virtually eliminate water from the planet while maintaining high levels of carbon dioxide, while Earth has retained much of its water and lost most of its atmospheric carbon dioxide."

Professor Taylor continues, "In the light of the new data it is possible to construct a scenario in which the climates on Venus and Earth were very similar when they started out, and then evolved to the state we see now, like twins separated at birth. Billions of years ago there is even the possibility that Venus would have been habitable."

Professor Andrew Coates of UCL's Mullard Space Science Laboratory, lead co-investigator of the electron spectrometer (part of ASPERA-4) said: "One of the evolutionary differences that has made Venus the Earth's 'evil twin' is that present-day Venus lacks a magnetic shield. This means that its atmosphere feels the onslaught of the solar wind and cosmic radiation, and has done for billions of years. We already know that Venus is a dry planet as the surface is so hot, but what we've found now is that Venus is still getting dryer. It loses hydrogen, helium and oxygen through its wake at a rate faster than similar escape from Mars."

Professor Coates adds, "These are all lost forever in the flowing solar wind. The ratio of hydrogen to oxygen being lost here is close to double, as we'd expect for water. The boundaries of the wake, where the bulk of this loss occurs, are found using data from our electron spectrometer."