What got you interested in studying Venus?
I have always been fascinated with the far off and the unknown. Like many boys I was obsessed with dinosaurs, but on my sixth birthday I watched Viking land on Mars, and I got hooked on planets. Venus is the most mysterious of all planets, shrouded in clouds and a surface so extreme the first Russian landers were crushed and melted. What made a planet so like Earth so different from it and so hostile to life? I studied geology at university and then a PhD just as NASA’s Magellan mission obtained the first global images of the surface using radar. To me, as a geologist, Venus is a beautiful planet. There’s nothing quite like the excitement of discovering a whole new world and starting to understand its differences.
What’s the weather like?
At the surface the temperature is 460˚C, hot enough to melt lead, tin, zinc and some aluminium alloys, but the pressure is also very high, at 90 atmospheres it is the same as 1000 m under the sea. The lower atmosphere is therefore more like the sea than an atmosphere, with slow moving currents and a near constant temperature from pole to pole. 50 km up in the clouds, where the pressure is the same as at sea level on Earth, the temperature is still hot but a rather more palatable 70˚C. However, Venus Express has shown an incredible active atmosphere at this layer, with wind speeds as fast as a TGV, and the clouds themselves are not made of water but of corrosive sulphuric acid.
Why are you sending a mission there?
For the first time Magellan mapped the whole surface of Venus and revealed a wide range of geological features - volcanoes, mountains, rifts, continent-like highlands - coexist with nearly a thousand impact craters distributed at random across the surface. The paradox is that the former signifies an active, geologically Earth-like planet, but the latter implies a uniform surface age. The proposed solution - a past global resurfacing event - suggests that all the apparent geological activity happened long ago. ESA’s Venus Express mission was sent to learn more about its atmosphere but in doing so it has uncovered evidence for recent geological activity that tells us our ideas were wrong. At the same time, we have started to discover Earth-sized planets around other stars but we don’t know if they are more like Earth or more like Venus. We need to go back to Venus to find out what makes Earth able to support life and Venus not.
How long will it take to get there?
Being the next planet in towards the Sun, Venus gets closer to Earth than any other planet, even than Mars. The journey to Venus is therefore fast by interplanetary standards, just 7 months. However, to achieve the mission goals, EnVision must spend several more months aerobraking - a technique first developed at Venus in which the spacecraft dips in and out of the upper atmosphere, using the atmospheric drag to slow down the spacecraft and so make its orbit lower and more circular without using any fuel. Venus Express has just completed an aerobraking phase, the insights from which have helped in planning the circularisation of EnVision’s orbit.
Is there water there?
There is water on Venus but a tiny amount in comparison with Earth and other planets. Most of it is locked up in the sulphuric acid droplets of the clouds. One of the aims of the mission is to find out whether Venus once had oceans that boiled away in a super-greenhouse, or whether it never had much water in the first place. Whichever was the case will help us to understand the very different evolutionary path that Venus took.
What are you hoping to learn?
Our main goal is to find out how active Venus is and in what ways. EnVision will have infrared mappers to detect the heat of volcanic eruptions and an imaging radar able to detect ground movements of just 1 cm and so find areas of active mountain building, rifting, and seismic activity. These will be supplemented by spectrometers to measure volcanic gases and a ground penetrating radar to provide our first look inside the planet. These experiments will help us to unravel the paradox between what the craters and the geology and so help us understand how Venus and Earth became so different.
If there is life on Venus what form would it be most likely to take?
People have speculated that there might be bacterial life in the clouds of Venus but the truth is that the conditions on the surface and in the atmosphere appear to be just a little too extreme in each respect – rather too hot, a bit too acidic, not enough water – for life as we know it. That said, scientists look at atmospheric anomalies, such as the coexistence of methane and oxygen, as an indicator of biological activity, and Venus has many such anomalies. Its sulphuric acid clouds would disappear relatively quickly without a source of sulphur dioxide and water. Such anomalies could imply life but most scientists believe that these types of anomaly are much more likely the result of geological activity – of just the type that EnVision is designed to detect.
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