Venus is alive – geologically speaking
ESA’s Venus Express has returned the clearest indication yet that Venus is still geologically active. Relatively young lava flows have been identified by the way they emit infrared radiation. The finding suggests the planet remains capable of volcanic eruptions.
It has long been recognised that there are simply not enough craters on Venus. Something is wiping the planet’s surface clean. That something is thought to be volcanic activity but the question is whether it happens quickly or slowly? Is there some sort of cataclysmic volcanic activity that resurfaces the entire planet with lava, or a gradual sequence of smaller volcanic eruptions? New results suggest the latter. “Now we have strong evidence right at the surface for recent eruptions,” says Sue Smrekar, a scientist at NASA's Jet Propulsion Laboratory in California.
The volcanic peak Idunn Mons That strong evidence comes in the form of compositional differences compared to the surrounding landscape in three volcanic regions. The data were collected by the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on ESA’s Venus Express spacecraft, which has been orbiting the planet since April 2006. VIRTIS records the brightness of surface rocks, providing an estimate of ‘emissivity’. In 2008, Jörn Helbert and Nils Müller, Institute of Planetary Research, German Aerospace Center, Berlin and co-authors on this new work, published a map of the variation of infrared emissivity across the southern hemisphere of Venus. Dr Smrekar and her colleagues targeted three regions that geologically resemble Hawaii, well known for its active volcanism. They show that the regions on Venus have higher emissivities than their surroundings, indicating different compositions. On Earth, lava flows react rapidly with oxygen and other elements in the atmosphere, changing their composition. On Venus, the process should be similar, though more intense because of the hotter, denser atmosphere, chiefly of carbon dioxide.
Artist's impression of Venus Express spacecraft The researchers interpret the fact that the lava flows appear to have different compositions from their surroundings as being evidence of a lack of surface weathering, indicating that the flows erupted relatively recently. They estimate that the flows are possibly as geologically recent as 2 500 000 years – and likely much less, possibly even currently active. “This is a significant result,” says Håkan Svedhem, ESA Venus Express Project Scientist. Whilst the gradual resurfacing scenario might not be the most spectacular, it does make Venus look a little more Earth-like. “There are some intriguing models of how Venus could have completely covered itself in kilometres of volcanic lava in a short time, but they require that the interior of Venus behaves very differently from Earth. If volcanism is more gradual, this implies that the interior may behave more like Earth, though without plate tectonics,” says Dr Smrekar.
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''Venus Express'' en orbite autour de Vénus

La sonde Venus Express, de l'Agence spatiale européenne (ESA), a découvert récemment des éléments prouvant que la planète Vénus, considérée comme géologiquement morte, serait peut-être encore active. En effet, des émissions infrarouges de coulées de lave à la surface ont été étudiées par la sonde. Ces coulées dateraient de 2,5 millions d'années — elles sont donc géologiquement récentes sachant que la majorité d'entre elles ont  ans. , a déclaré Håkan Svedhem, de l'équipe scientifique de Venus Express.

Venus Express est la première mission d'exploration de l'ESA en direction de Vénus et la première à la visiter depuis le programme Magellan de la NASA en 1994. D'un poids de  kg, elle a été lancée en novembre 2005 et est totalement opérationnelle depuis mai 2006. Les opérations sont conduites depuis le Centre européen d'opérations spatiales (ESOC), situé à Darmstadt, en Allemagne. La fin de la mission est prévue pour fin décembre 2012.