VENUS
NASA/JPL-Caltech
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Formation Like the other planets, Venus is thought to have been formed from the solar nebula, about 4.5 billion years ago. This massive, swirling cloud of gas and dust slowly condensed, forming planetesimals (small bodies of heavier materials like silicates and metals) which then collided with each other, forming larger bodies and ultimately, the terrestrial planets.
Venus spins backward compared to most of the other planets. On Venus, the Sun rises in the West and sets in the East. Its spin is so slow that one rotation around its axis takes longer than one complete orbit of the planet around the Sun, This means that on Venus, a day is longer than a year. |
Radar generated image of Venus' surface (NASA/JPL)
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Structure, Atmosphere and Magnetosphere Venus is often called “Earth’s twin”. Like Earth, it is a rocky planet, but slightly smaller. It has similar gravity, about 91% of Earth’s. Despite these basic similarities, Venus is unlike Earth in many important ways. It has an extremely thick atmosphere, mostly comprised of carbon dioxide (96%). The atmospheric pressure on the planet surface is about 93 times that of Earth, equivalent to the pressure found 900 meters below sea level on Earth. Walking on the surface of Venus would feel a bit like walking under water on Earth.
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The high concentration of carbon dioxide traps heat from the Sun, and makes Venus the hottest planet in the Solar System. The average surface temperature on Venus is a scorching 464 degrees Celsius. If Venus had water in the distant past, it would have vaporized long ago, then dissipated into space.
Because of its thick clouds and atmosphere, the surface of Venus cannot be seen through a telescope. Images of the surface are available from landers and from radar mapping by orbital probes. Most of the surface shows smooth volcanic plains, with two large highlands, called “Ishtar Terra” and “Aphrodite Terra”. Venus has well over 150 large volcanoes, and there is good evidence that at least some are still active. The highest peak on Venus is Maxwell Montes. At 11 km in height, it is about 25% higher than Mount Everest (measured from sea level). |
The Maat Mons is an 8 km high volcano. (NASA/JPL)
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Radar Images of Venus show about 1000 large meteor impact craters (more than 3 km diameter). Most are in “pristine” condition, owing to the lack of erosion and plate tectonics on Venus’ surface. There are no small craters. The thick atmosphere causes small meteors to vaporize before hitting the surface, or to slow down so much that they do not leave craters on impact.
There is little direct evidence describing Venus’ internal structure. It is thought to be like Earth's - an outer crust overlaying an internal rocky mantle, which surrounds a metallic core. Unlike Earth, there are no plate-tectonics on the surface. It is thought that once every 300-600 million years the surface crust collapses into the mantel, then reforms through a series of volcanic eruptions. |
Three craters with diameters ranging from 37 to 50 km (NASA/JPL)
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Venus has no internally-generated magnetic field. Its weak magnetic field is caused by an interaction between its ionosphere and the Solar Wind.
Observation of Venus As seen from Earth, Venus is the brightest object in the sky, after the Sun and the Moon. It is always within 47 degrees of the Sun. Historically, it has been called the “Morning Star” and the “Evening Star”, depending on which side of the sun it appears on when observed from Earth. Because it is closer to the Sun than the Earth, it shows phases, like our moon. It can be intensely bright and is sometimes mis-reported as a UFO. When observing Venus, great care must be taken to avoid looking at the Sun because of the high risk of permanent eye damage
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Transit of Venus Occasionally, Venus travels across the disk of the Sun, as seen from Earth. These events are called “transits.” Because of the orbital characteristics of the Earth and Venus, two transits occur 8 years apart, then there is a long wait of either 105 or 121 years until the next pair of transits.
Transits of Venus have been extremely important in the history of astronomy. By carefully timing the transit’s duration from two widely separated locations on Earth, astronomers could more accurately determine the distance from the Earth to the Sun, and the overall size of our solar system. |
Multiple exposures showing the 2014 Venus transit across the sun.
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Moons Venus has no moons, although some theories suggest that in may have had a moon in the distant past. Interaction with such a moon might explain Venus’ backward rotation.
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Missions The Soviet Venera program and NASA’s Mariner program sent a variety of probes to Venus in the 1960's and 1970's. Mariner 2 (1962) was the world’s first successful interplanetary mission. Venera 4 (1967) was the first interplanetary probe to successfully capture data while in the environment of another planet. Venera 7 (1970) was the first spacecraft to land on another planet, and Venera 9 (1975) was the first to return images from the surface of another planet. The Soviet Venera program ended in 1983 with Venera 15 and 16 orbiting Venus, mapping the surface. From the 1980's onward, there have been many flybys and orbital missions conducted by NASA, ESA and JAXA (the Japanese Space agency). Recently, BepiColombo (ESA/JAXA) transmitted images from a Venus flyby, while on its way to Mercury.
https://www.esa.int/var/esa/storage/images/esa_multimedia/images/2020/10/venus_setting/22264138-3-eng-GB/Venus_setting_pillars.gif |
Mariner 2 - the first successful interplanetary spacecraft (NASA/JPL)
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