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Venus is Earth’s closest relative, but the atmospheres of both planets are radically different. EU-funded project EUROVENUS explored Venus – the closest object to Earth other than the moon – in a bid to advance knowledge on why the two planets are poles apart.
The brightest ‘star’ in the sky was formed at a similar place in the solar system as Earth, it is comparable in size, is made of the same materials, is approximately the same age, and is at a similar distance from the sun. But that is where the similarities end. Venus rotates in the other direction – so the sun rises in the West and sets in the East – and one Venus day lasts longer than one Venus year because the planet spins so slowly.
“Venus is a mythical object, part of humankind’s cultural heritage, but we know so little about it. We don’t know if it has active volcanoes, or if there was an ocean in the past with forms of life. It is really inspiring to know that very close to us there is still a full world to map and discover,” says Thomas Widemann from the Observatoire de Paris, Université Versailles St-Quentin and EUROVENUS project coordinator.
Intense greenhouse effect
Our closest planetary neighbour is covered with a thick layer of sulphuric acid clouds. While the clouds reflect sunlight and the sun’s warmth away, the greenhouse effect they cause is so intense that the atmospheric temperature reaches 450 °C. The planet also experiences much stronger, spiralling winds.
Venus could therefore indicate what happens when climate change goes out of control, perhaps giving clues to the Earth’s future. Currently, climate change on Earth is still limited to a rise of 2 or 3 °C, but it is happening very fast.
During the project, EUROVENUS scientists explored the middle and lower atmosphere of Venus. They used data collected by the Venus Express spacecraft launched by the European Space Agency in 2005, which orbited Venus from April 2006 to December 2014, and very powerful Earth-based telescopes located in Hawaii.
The project built a climatology of Venus’ very dense atmosphere where the atmospheric pressure is 100 times greater than that of the Earth. It also explored the composition of the atmosphere, its wind systems, atmospheric electricity and lightning, its temperature and energy balance, and the planet’s exchanges with space.
“EUROVENUS has considerably increased our knowledge of the structure of Venus’ atmosphere. The European research teams it sponsored over three years achieved several major scientific findings,” says Widemann.
Looking far and beyond
The team used the Earth-based telescopes to gauge the speed of cloud particles by measuring the sunlight they reflect. Alongside data collected by Venus Express, EUROVENUS showed that the velocities of individual cloud particles are the same as those calculated from previously collected cloud imagery. “This confirmed that decades of cloud-tracking observations dating back to the 70s were representative of true atmospheric circulation on Venus,” explains Widemann.
The project also confirmed that the atmosphere on Venus at cloud-top level spins some 60 times faster than the planet itself. The explanation of this super-rotation effect remains a long-standing question in solar-system atmospheric studies. The project also gathered new data on sulphur dioxide in the atmosphere which may indicate the presence of active volcanoes on the planet.
EUROVENUS has helped Europe stay at the cutting-edge of Venus exploration and in the emerging field of comparative planetology. Although the project has ended, several space agencies are discussing a future mission to planet Venus. The European proposal for a new mission – EnVision – has been put forward by two EUROVENUS partners.