Venus is the third brightest object in the sky, after the sun and the moon. It is surrounded by very thick clouds of cardon dioxide and nitrogen that trap the incoming light into the surface. The high density of the atmosphere allows the pressure at the air surface to reach 90 times that of the earth.
The surface temperature of Venus never reaches below 400 degrees Celsius. Rather, it is around 450 degrees at the lowland areas at the equator. This makes Venus the hottest planet in the solar system, despite the fact that Mercury is almost twice as close to the sun.
Its orbit takes it 108 million kilometres from the sun, on average, and is always closer to the sun than the Earth. Like Mercury, Venus is always observed close to the sun. Stargazers in the past called Venus the Evening star or the Morning star.
Because it is closer to the sun than the Earth, it is possible to see phases of Venus (and Mercury), like we see phases of the moon.
Strangely, Venus spins retrogradely (very slowly: -243 Earth days), which means that it rotates from east to west, instead of west to east. This suggests a collision in the past: the axis which Venus spins around tilts 177 degrees - about the same as Uranus! While one day at Venus is 243 Earth days, the time it takes to complete an orbit is 225 Earth days (a venusian year), which makes a day longer than a year!
Venus's atmosphere (P)
Venus surface (P)
As mentioned above, Venus's atmosphere consists mainly of carbon dioxide and some nitrogen, but there is also sulphuric acid present. There is a shortage of water vapour. The atmosphere allows incoming light, but it does not allow it to escape. In turn, this leads to a strong greenhouse effect.
Though most of the incoming light is reflected into space again: Venus albedo is about 0.60 (the amount reflected light in %), hence most of the light will never reach the surface.
The temperature, which lies around 450 °C does not lower itself significantly during the night due to the fact that the strong winds spread the heat rapidly around the planet, some clouds circle the planet in 4 days.
The clouds consist mainly of sulphur dioxide and sulphuric acid, which has lead to the corrosion of spacecraft attempting to land on Venus. The temperature at the clouds reaches -45 °C.
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Since the thick atmosphere blocks the view of the surface completely, spacecraft have to use other measures to study the planet, like using radar.
Impact craters are rare on Venus, compared to for instance Mercury, because the dense and thick atmosphere heats the meteors so they burn up at the entry. It is to be noted that no craters have been found that are smaller than 1.5-2 km across.
Though there is no waterflow, other processes contribute to errosion on the surface, like the slow, but hot winds at the surface. It is possible that the atmosphere chemically erodes/alters the rocks.
During the history of the terrestrial planets two periods are distinct. The first is the very early period of bombardment starting when the planets started to cool down and got solid crusts. At this period of time there was very much debris, rocks and asteroids in the solar system that hit the surfaces of planets.
These impacting objects probably existed earlier too, but since the planets didnt have solid crusts, the impacts craters didnt last. The second period is also of bombardment of comets and asteroids, but it occurred more recently. Venus shows no signs from that period, which suggests that Venus was completely resurfaced 300 to 500 million years ago.
There are large highland areas that stretch across the vast mountainous plains of the Venus. In the north is the area called Ishtar Terra, which has the highest mountains of Venus, called Maxwell Montes. Ishtar Terra is approximately the size of Australia and is a lava-filled basin. In the south is the area called Aphrodite terra, and area that is larger than half the size of Africa and extends for almost 10 000 km. All surface features, except Maxwell Montes are named after females.
It is believed that Venus does not have the same kind of plate-techtonics like earth, and the slow retrograde rotation is not fast enough to sustain a powerful magnetic field, which Venus lacks.
Because the surface is so hot, some metals evaporate, in particular the metal lead. At the surface it would exist as mist. When the evaporated lead would rise higher into the atmosphere, where it is colder, it would condense to become solid/liquid again. This would explain why the highlands of Venus are so bright.
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Exploration of Venus
A number of spacecraft has been sent to Venus, the first successful being the american Mariner 2 (though a russian attempt was made in 1961 with Venera 1). On March 1, in 1966 Venera 3 became the first probe to crash-land on Venus. Venera 2 had failed to land due to overheating. The russians have sent atleast 16 Venera probes to study Venus, several of them have landed on the surface and sent back pictures showing a warm, but dead world.
The sky looks like on Earth on an overcast sky, though the sky is more yellow/orange.
Between 26 October - 25 November 2005, the European Space Agency, ESA is planning on sending a spacecraft, Venus Express to Venus. It will study the Venusian atmosphere and clouds in detail and make global maps of the surface temperatures.
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Average distance from sun:
108 208 930 km.
Equatorial Radius: 6 051.8 km.
Mass: 4.8685 x 10^24 kg.
Density: 5.24 g/cm^3.
Escape Velocity: 10.36 km/s.
Length of day: -243 Earth days (retrograde).
Length of year: 224.7 Earth days.
Mean Orbit Velocity: 35.021.4 km/s.
Equatorial Inclination to Orbit: 177.3 degrees.
Min./Max. Surface Temperature: 462 °C.
Atmosphere: Carbon dioxide 97%, Nitrogen 3%+.
Above: Venus, our twin planet. From space it reveals nothing to the human eye. A thick layer of clouds that traps the heat from the sun has enshrouded the surface. At a height of 90 km, the cloud layer becomes impenetrable in visible light.
Venus is known to have volcanic activity, and lightning storms have been detected on the 500 K warm planet. Astronomers have observed very few craters on the surface, which leads them to believe that the entire surface of Venus was reshaped in a cataclysmic event 300 - 1 000 million years ago.
This illustration is available upon request, as a Print (6000x4500 pixels, 300 dpi).
Above: Venus's surface is practically windless, but the temperature reaches infernal levels (500 C/900 F). Scientists have discovered volcanoes on the surface, and they have also detected lightning. Here you see lightning in an ash cloud.
This illustration is available upon request, as a Print (6000x3750 pixels, 300 dpi).
Space Art 1: Venus surface is veiled by a thick layer of clouds, which both reflect the light and trap what light reached the surface from leaving it.
Illustration 1: Illustration: Venus radar image, without its clouds