What Can You See in the Night Sky This Week? Venus!

6 February 2012 by Anonymous (not verified)

Venus – Earth's sister planet – is the hottest planet in our solar system. It has a sizzling surface temperature of 460 C (860 F). To put that into perspective, the highest recorded temperature on Earth was 57.8 C in Libya on the 13th September, 1922 – around 10% of Venus's average surface temperature. Venus is the second rock from the Sun and is the brightest object in the night sky after the moon, writes Jas Virdee.

Venus is named after the Roman Goddess of love and beauty and can be seen from as early as 17:30 in the West. It falls below the horizon only two hours later but it's impossible to miss because of its brightness. So why is Venus so hot and bright? After all, it's not the closest planet to the sun (Mercury) nor the closest planet to Earth (Mars). The answer to both questions lies in Venus's atmosphere which is 96.5% carbon dioxide – a powerful greenhouse gas which traps the sun's heat. Venus is nearly 40% closer to the Sun than we are and its atmosphere is almost 100 times more massive then ours, increasing its ability to trap heat. Thus, an extreme form of the greenhouse effect is occurring on Venus making it far too hot for humans. Venus's thick clouds account for its brightness, reflecting over 65% of the sun's light. However, this means we can't see the surface using visible light. On October 22nd 1975, the Russian spacecraft Venera 9 landed a detachable probe on the surface of Venus and became the first spacecraft to transmit a picture from the surface of another planet.

Images of Venus's Surface from Venera 9 (top) and Venera 10 (bottom)

Venus is almost the same size as the Earth and early conditions are thought to have been similar. Venus is thought to have harboured vast water oceans and possibly primitive forms of life. But if Venus was like the early Earth – why did runaway global warming occur? Three billion years ago, the Sun was 30% less luminous than it is now resulting in cooler atmospheric temperatures. In addition, Venus lacks a magnetic field which deflects the solar wind away from the planet's atmosphere; the result was the loss of many of the lighter molecules in the atmosphere like hydrogen and water vapour – leaving behind heavier greenhouse gases like carbon dioxide. The net effect was a slow but steady increase in the temperature which boiled the water away into outer space. Here is an animation of the Sun stripping Venus's atmosphere

How do we know all of this? Since the beginning of the space race between the Soviet Union and the USA there have been over 40 space missions which have flown to or past Venus. About half of them failed – most of them in the early days of space exploration. The latest mission to Venus is the ESA (European Space Agency) sponsored Venus Express which has been in orbit for over nearly 6 years. This mission is focused on unlocking the secrets of Venus's atmosphere – doing so holds valuable lessons for our understanding of Earth's atmosphere and our influence on it.

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