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Earth's evil twin. Appearances can be deceiving. This thick, cloud-rich atmosphere rains sulphuric acid and below lie not oceans but a baked and barren lava-strewn surface. Welcome to Venus. The second planet from the Sun is often coined Earth's ?evil twin' on account of it being almost the same size but instead plagued with a poisonous atmosphere of carbon dioxide and a sweltering 470zC surface. Its high pressure and temperature is hot enough to melt lead and destroy the spacecraft that dare to land on it. Thanks to its dense atmosphere, it is even hotter than planet Mercury, which orbits closer to the Sun. ESA's Venus Express studied the planet from orbit between 2006 and 2014, providing the most in-depth studies of its atmospheric circulation to date. This false-colour image was taken in ultraviolet light with the Venus Monitoring Camera on 23 July 2007. It shows a view of the southern hemisphere from equator (right) to the pole (left) from a distance of 35 000 km from the surface of the planet. Scientists think that Venus once looked a lot like Earth, but underwent an irreversible climate change that is often used as an extreme example of what happens in a runaway greenhouse effect. The main source of heat in the Solar System is the Sun's energy, which warms a planet's surface up, and then the planet radiates energy back into space. An atmosphere traps some of the outgoing energy, retaining heat ? the so-called greenhouse effect. It is a natural phenomenon that helps regulate a planet's temperature. If it weren't for greenhouse gases like water vapour, carbon dioxide, methane and ozone, Earth's surface temperature would be about 30 degrees cooler than its present +15zC average. Over the past centuries, humans have altered this natural balance on Earth, strengthening the greenhouse effect since the dawn of industrial activity by contributing additional carbon dioxide