Stardate: Mysteries of Venus celebrates the arrival of the first European Space Agency (ESA) probe in orbit about Venus. We'll introduce the planet Venus and the Venus Express mission and discuss why scientists are so interested in finding out more about Venus, and show you what Venus's surface is like. Pausing to consider how Venus appears in our own sky, we'll then look at the hot, dense atmosphere of Venus that has turned what would otherwise be an Earth-like planet into a gruesomely hostile place. However, as we learn, some scientists think it is possible that microscopic life could exist within Venus's clouds.
Venus and Venus Express
Venus ought to be Earth's twin. Its size, mass and density are all very similar to Earth's. However, the evolution of its surface and atmosphere have progressed in very different ways to Earth's. The fundamental reason for this difference may simply be that the distance between Venus and the Sun is a little less than three-quarters of the Earth-Sun distance. Its relative closeness to the Sun means that nearly twice as much solar energy hit Venus than hits the Earth. If Venus ever did have oceans these completely evaporated billions of years ago, yielding a permanent cloud layer that shrouds the surface from direct observation.
Venus's permanently cloudy atmosphere seen by Pioneer Venus orbiter in 1979 [Image: NASA]
The extra water vapour that this evaporation added to the atmosphere trapped the solar heat, and made Venus even warmer. Carbon dioxide in the atmosphere added to Venus's 'greenhouse effect' (leading to today's mean surface temperature of about 470oC), whereas on the Earth most of the atmospheric carbon dioxide has been extracted into limestone, a kind of rock that can form only under water. Discover what we already know about Venus's atmosphere.
The loss of Venus's water means that the whole rocky shell of the planet behaves differently to the Earth's. There is no 'plate tectonics', planet-wide volcanism appears to be concentrated into brief, catastrophic outbursts every half billion years or so, and there is no flowing water to erode the surface. Spend some time with us getting to know Venus terrain.
The terrain on Venus has been mapped from orbit using radar techniques, notably by the NASA Magellan mission (1990-1994). There were also a number of Soviet landers that survived on the hostile surface long enough to transmit some pictures and chemical analyses.
The surface of Venus as seen by the Venera 13 lander in 1982. Part of the lander can be seen at the bottom, and beyond that a landscape of slab-like rocks, with the characteristics of basalt lava flows.
Apart from its atmosphere and surface, other peculiarities that help to make Venus different from the Earth are its slow rotation and (possibly related) lack of a strong magnetic field. Venus rotates much more slowly than the Earth; in fact it takes longer to spin on its axis (243 Earth-days) than it does to go round the Sun (225 Earth-days). This means that from the surface of Venus, if you could ever see the Sun through the cloud, it would rise in the west and set in the east, taking 58 Earth-days between sunrise and sunset.
An ESA mission, Venus Express, will arrive in orbit around Venus in April 2006, designed especially to study the atmosphere. The name Venus Express comes from the short time taken to prepare and launch the mission, less than three years between approval and launch. To achieve this, the ESA re-used the design of the Mars Express mission and the same industrial teams that worked on that mission.
Venus Express launched on a Soyuz Fregat rocket from the Baikonur Cosmodrome, Kazakhstan, on 9 November 2005 [Image: ESA / STARSEM-S. CORVAJA]
Artist's impression of Venus Express in orbit about Venus [Image: ESA]
For the latest on the mission, and all the background details, visit the ESA Venus Express site;
You can find out more about the planet on NASA's guide to Venus;
and gain access to many more spacecraft views of the planet with the Venus Planetary Photojournal.
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About our expert
Dave Rothery is a volcanologist and planetary scientist at the Open University. His current research includes studying volcanic eruptions on the Earth and the characterising planetary surfaces. He chairs the OU's planetary science courses and the geology residential school course.