Venus is our inner neighbour in the Solar System. The second planet from the Sun, it is another rocky world, similar in size to the Earth. But it could hardly be more different or less hospitable.
Venus is a beautiful and brilliant sight in our skies, becoming the brightest object after the Sun and Moon. It is named after the Roman goddess of love, but in reality it is a hateful place that conjures up a vision of hell.
Space probes have shown that our fiery cousin, devoid of water and permanently shrouded in cloud, is a nightmare world with a climate that has gone out of control. Its clouds mean it gets less sunlight than we do, despite being closer to the sun.
A runaway greenhouse effect has made it the hottest planet in the Solar System with a temperature on the ground that is twice that inside a domestic oven – 465C.
Air pressure at the surface is 100 times greater than on Earth. Its atmosphere is almost entirely poisonous carbon dioxide. There is no water but toxic clouds of sulphuric acid belched by volcanoes.
It is only comparatively recently that, thanks to space probes, we have learned this because Venus is enveloped by a dense cover of clouds. These clouds hide the surface of the planet from us completely and astronomers could only speculate as to what lay at the surface.
Some imagined vast oceans as the source of the clouds. Others suggested the surface was covered by Saharan-type deserts. The clouds must reflect around 60 per cent of the sun’s light and heat. So its fiery conditions are thought due to a runaway greenhouse effect.
Early clues that all was not well on Venus came when the former Soviet Union sent a sequence of probes named Venera to the planet.
It was not long before they sent back the first data revealing Venus’ searing temperatures, extreme atmospheric pressure at the surface, 90 times greater than on Earth, plus raging thunderstorms. Four probes – Venera 9, 10, 13 and 14 – even transmitted images of the planet’s rocky terrain in the minutes before they were crushed to destruction.
Later probes manged to lift the veil from Venus even more. Two American Mariner missions learned more about the make-up of the atmosphere – mainly carbon dioxide with some nitrogen – and pictured the patterns in the cloud tops. But the greatest flood of information came when the US spacecraft Magellan sailed into orbit around Venus in 1990 and began to chart its surface in detail with cloud-penetrating radar.
Magellan was a stunning success, allowing planetary scientists to draw up high-resolution maps of Venus before the probe was deliberately plunged into the atmosphere in 1994. These maps showed that the totally dry surface was mainly made up of smooth plains with two continent-sized highland areas, one in the northern hemisphere, now named Ishtar Terra, and one in the southern, called Aphrodite Terra.
Most of the mountains and other surface features were named after historical and mythological women in keeping with the planet’s own female persona. Features detected include 167 giant volcanoes and nearly 1,000 impact craters.
In 2006 a European space probe, Venus Express, went into orbit around the planet dubbed Earth’s evil twin and began returning fascinating new data including close-up images of a swirling double vortex over the south pole. In an eight-year mission, its swooping orbit brought it low over the cloud tops and revealed big variations in the sulphur dioxide content, suggesting that the volcanoes were still active. Its fuel exhausted, Venus Express plunged to destruction in the planet’s atmosphere in early 2015.
A Japanese space probe called Akatsuki, launched towards Venus in 2010, looked lost after a fault caused it to fly past the planet. But five years later, mission controllers managed to rescue it and put it into a new, more elongated orbit where it began to survey the atmosphere.
Two NASA missions to the outer planets also gathered data on Venus as they flew past to get a gravitational boost on their long journeys. Galileo shot past on its way to Jupiter, in February 1990, taking pictures, measuring dust, charged particles and magnetism, and making infrared studies of the lower atmosphere. Saturn probe Cassini-Huygens made two flybys, in April 1998 and April 1999, when it looked for, but failed to spot, lightning in the clouds.
Related: Here’s how to observe Venus.