As our own planet gets ever more crowded and its natural resources used up, it would be nice to know there was a “back-up” Earth not too far away: a place with pristine forests and deserts, tropical temperatures and vast, unpolluted oceans. Until quite recently it seemed that there was, for this was our vision of Venus — our nearest neighbouring planet and Earth’s near equal in size and mass. Astronomers have studied this brilliant object in the night sky for centuries and speculated about what lies beneath the layers of bright, featureless cloud that can be seen with even a small telescope.
Given that Venus is only two-thirds as far from the Sun as the Earth is, and therefore receives roughly twice as much sunlight, it might seem strange that astronomers should have thought that Venus was a tropical paradise. But all that cloud more than compensates by increasing the planet’s reflectivity and reflecting much of the solar energy. Also, since the Earth and Venus probably formed together in the same region of the primordial cloud of dust and gas that orbited the Sun about 4.5 billion years ago, it is reasonable to expect that the two planets have similar compositions. For instance, there should be enough water on Venus to modify the surface and atmosphere, perhaps even enough to form a deep ocean.
By the 1960s we even had the rocket technology to take us to this fantastic new world. But it was not long before our new space-faring capability shattered our romantic picture of Venus. Indeed, by the time that the first successful interplanetary space mission — NASA's Mariner 2 — arrived at Venus in December 1962, results from ground-based telescopes had already hinted that Venus might not be what it seemed. Now, almost half a century later, we have the clearest view yet of our planetary neighbour.
In the March issue of Physics World, Fred Taylor discusses how the first results from the European Space Agency’s Venus Express mission, launched in November 2005, have reshaped our understanding of the other blue planet.
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