Venus as a more Earth-like planet

Still delivering ESA's Venus Express probe has been in orbit since April 2006. Eight research papers in this issue present new results from the mission, covering the atmosphere, polar features, interactions with the solar wind and the controversial matter of venusian lightning. Håkan Svedham et al . open the section with a review of the similarities and (mostly) differences between Venus and its 'twin', the Earth. Andrew Ingersoll considers the latest results, and also how the project teams plan to make the most of the probe's remaining six years of life. Venus is Earth's near twin in mass and radius, yet its atmosphere, mostly composed of carbon dioxide, has a surface temperature and pressure far higher than those of the Earth. This paper discusses the first year of observations by Venus Express, which bring into focus the evolutionary paths by which the climates of two similar planets diverged from common beginnings to such extremes. Venus is Earth’s near twin in mass and radius, and our nearest planetary neighbour, yet conditions there are very different in many respects. Its atmosphere, mostly composed of carbon dioxide, has a surface temperature and pressure far higher than those of Earth. Only traces of water are found, although it is likely that there was much more present in the past, possibly forming Earth-like oceans. Here we discuss how the first year of observations by Venus Express brings into focus the evolutionary paths by which the climates of two similar planets diverged from common beginnings to such extremes. These include a CO 2 -driven greenhouse effect, erosion of the atmosphere by solar particles and radiation, surface–atmosphere interactions, and atmospheric circulation regimes defined by differing planetary rotation rates.