The second planet out from the Sun is Venus. And Venus is bright, very bright. In the night sky it is second only to the Moon. And because it is closer to the Sun than the Earth, it always appears in the same region of space as the Sun. In practice, this means it is most visible to us just before sunrise or just after sunset. It is usually seen low against the horizon.
At first it was thought that this bright object was two distinct stars. As a result the morning star was given the name of Phosphorous and its evening sister was called Hesperus. However by the 5th Century BCE, its true nature has become understood. Venus has over the centuries led many to believe that if life were present anywhere else in the solar system, it would be found here. For those believers, there was a certain amount of circumstantial evidence to back their theory.
The planet is similar in size to the Earth. At 7,521 miles, it is only about 400 miles shorter in diameter. It is closer to the Sun at an average distance of 67 million miles compared with the Earth’s at 93 million miles. So it was agreed that it would be warmer there. Perhaps it would be too hot?
However the factor that seemed to oppose this reasoning was that Venus was covered in dense clouds. And it was these clouds that reflected the sunlight which made Venus appear to be so bright. But to those believers it also indicated that the surface would be protected against the additional heat from the Sun. When they tried to find an analogy on the Earth, they surmised that it could be similar to a tropical rain forest. This meant that they might be able to expect a warm, moist atmosphere leading to dense vegetation, water and life.
Unfortunately they were wrong. In fact they probably couldn’t have got it more wrong. The clouds that reflect the sunlight back into space do not consist of water vapour but of sulphuric acid. Not very inviting I’m sure you’ll agree. However, the main constituent of Venus’ atmosphere is carbon dioxide. It’s so thick that the atmospheric pressure on the surface is 90 times that of the Earth.
It is a case of the greenhouse effect gone mad in the extreme. These clouds are responsible for two effects on the surface of the planet. They black out most of the sunlight so that everything appears dull. But it has another far more damaging effect. Pretty much everyone has heard of global warming these days and how the build-up of carbon dioxide in the atmosphere can lead to a rise in temperature. Well, on Venus, the temperature has risen – to a scorching level of 600º Celsius. This is hotter than the surface of Mercury which is much closer to the Sun. Perhaps there is a lesson for us all here? With such temperatures, there is no chance of life – well, not as we know it, of course.
So, do we know what the surface of Venus looks like? The answer is “yes” because it is possible to view the surface through the clouds by using wavelengths other than the visible spectrum. The space probe Magellan was sent to Venus in the 1990s and it used radar to penetrate the cloud cover and photograph the surface. Many other probes have been sent there and at present, the number is over 40. They have either flown by, orbited or have actually landed on the surface.
We know that Venus is a rocky planet which consists of a nickel-iron core surrounded by a molten layer of the same material. Then there is a rocky mantle and finally, a silicate crust. The surface appears volcanic with vast fields of solid lava. There are also some highland regions. It is possible that some of the volcanos may still be active. But this all leads us to the conclusion that Venus is definitely not a planet which will be suitable for us to visit in person.
Like Mercury, Venus does not have any moons in orbit around it. However, whilst we’re on the subject of orbits, Venus does have a couple of interesting aspects to its orbital characteristics. Unlike most other planets in the solar system including the Earth, Venus rotates in the opposite direction. Therefore, to an observer on the surface, the Sun would rise in the west and set in the east.
The other really interesting aspect of Venus concerns its period of rotation. The day on Venus lasts longer than its year. Whereas our day is slightly less than 24 hours, Venus’ day is 243 Earth days long. And whilst our orbital period is just over 365 days, Venus’ year is 224 Earth days long. Pretty strange I’m sure you’ll agree.
So because Venus is inhospitable to life, it has shown us a possible future picture of doom and what the Earth could become if we let global warming run completely out of control.
John Pullen 