Venus is the second planet from the Sun and the sixth largest. Venus' orbit is the most nearly circular of that of any planet, with an eccentricity of less than 1%.
History of VenusVenus (Greek: Aphrodite; Babylonian: Ishtar) is the goddess of love and beauty. The planet is so named probably because it is the brightest of the planets known to the ancients. (With a few exceptions, the surface features on Venus are named for female figures.)
Venus has been known since prehistoric times. It is the brightest object in the sky except for the Sun and the Moon. Like Mercury, it was popularly thought to be two separate bodies: Eosphorus as the morning star and Hesperus as the evening star, but the Greek astronomers knew better. (Venus's apparition as the morning star is also sometimes called Lucifer.)
Since Venus is an inferior planet, it shows phases when viewed with a telescope from the perspective of Earth. Galileo's observation of this phenomenon was important evidence in favor of Copernicus's heliocentric theory of the solar system.
The first spacecraft to visit Venus was Mariner 2 in 1962. It was subsequently visited by many others (more than 20 in all so far), including Pioneer Venus and the Soviet Venera 7 the first spacecraft to land on another planet, and Venera 9 which returned the first photographs of the surface. The first orbiter, the US spacecraft Magellan produced detailed maps of Venus' surface using radar. ESA's Venus Express launched in November of 2005 and arrived at Venus in April 2006. The Venus Express is conducting atmospheric studies, mapping the Venusian surface temperatures and the plasma environment.
Venus' rotation is somewhat unusual in that it is both very slow (243 Earth days per Venus day, slightly longer than Venus' year) and retrograde. In addition, the periods of Venus' rotation and of its orbit are synchronized such that it always presents the same face toward Earth when the two planets are at their closest approach. Whether this is a resonance effect or merely a coincidence is not known.
Venus is sometimes regarded as Earth's sister planet. In some ways they are very similar:
- Venus is only slightly smaller than Earth (95% of Earth's diameter, 80% of Earth's mass).
- Both have few craters indicating relatively young surfaces.
- Their densities and chemical compositions are similar.
The pressure of Venus' atmosphere at the surface is 90 atmospheres (about the same as the pressure at a depth of 1 km in Earth's oceans). It is composed mostly of carbon dioxide. There are several layers of clouds many kilometers thick composed of sulphuric acid. These clouds completely obscure our view of the surface. This dense atmosphere produces a run-away greenhouse effect that raises Venus' surface temperature by about 400 degrees to over 740 K (hot enough to melt lead). Venus' surface is actually hotter than Mercury's despite being nearly twice as far from the Sun. Venus has a vortex at each pole. These vortices rotate vertically and recycle the atmosphere downwards. The north polar vortex has a peculliar double eye shape surrounded by a collar of cool air; it makes a complete rotation in three Earth days.
Venus probably once had large amounts of water like Earth but it all boiled away. Venus is now quite dry. Earth would have suffered the same fate had it been just a little closer to the Sun. We may learn a lot about Earth by learning why the basically similar Venus turned out so differently.
Most of Venus' surface consists of gently rolling plains with little relief. There are also several broad depressions: Atalanta Planitia, Guinevere Planitia, Lavinia Planitia. There two large highland areas: Ishtar Terra in the northern hemisphere (about the size of Australia) and Aphrodite Terra along the equator (about the size of South America). The interior of Ishtar consists mainly of a high plateau, Lakshmi Planum, which is surrounded by the highest mountains on Venus including the enormous Maxwell Montes.
Data from Magellan's imaging radar shows that much of the surface of Venus is covered by lava flows. There are several large shield volcanoes (similar to Hawaii or Olympus Mons) such as Sif Mons. Recently announced findings indicate that Venus is still volcanically active, but only in a few hot spots; for the most part it has been geologically rather quiet for the past few hundred million years.
There are no small craters on Venus. It seems that small meteoroids burn up in Venus' dense atmosphere before reaching the surface. Craters on Venus seem to come in bunches indicating that large meteoroids that do reach the surface usually break up in the atmosphere.
The oldest terrains on Venus seem to be about 800 million years old. Extensive volcanism at that time wiped out the earlier surface including any large craters from early in Venus' history.
Magellan's images show a wide variety of interesting and unique features including pancake volcanoes (left) which seem to be eruptions of very thick lava and coronae (right) which seem to be collapsed domes over large magma chambers.
The interior of Venus is probably very similar to that of Earth: an iron core about 3000 km in radius, a molten rocky mantle comprising the majority of the planet. Recent results from the Magellan gravity data indicate that Venus' crust is stronger and thicker than had previously been assumed. Like Earth, convection in the mantle produces stress on the surface. However on Venus the stress is relieved in many relatively small regions instead of being concentrated at the boundaries of large plates as is the case on Earth.
Venus has no magnetic field, perhaps because of its slow rotation.
Venus has no satellites, and thereby hangs a tale.
Venus is usually visible with the unaided eye. Sometimes (inaccurately) referred to as the "morning star" or the "evening star", it is by far the brightest "star" in the sky. There are several Web sites that show the current position of Venus (and the other planets) in the sky. More detailed and customized charts can be created with a planetarium program.
On June 8 2004, Venus passed directly between the Earth and the Sun, appearing as a large black dot travelling across the Sun's disk. This event is known as a "transit of Venus" and is very rare: the last two were in 1882 and 2012, for the next you'll have to wait until 2117. While no longer of great scientific importance as it was in the past, this event was the impetus for a major journey for many amateur astronomers.
More about Venus
- more Venus images
- from NSSDC
- Venus Revealed Images by David Grinspoon
- Magellan mission home page
- Venusian Craters and Venusian Volcanic Features from LANL
- Magellan Venus Explorer's Guide from JPL; about Magellan and Venus prior to the Magellan data
- Guide to Magellan Image Interpretation from JPL
- The Magellan Spacecraft at Venus by Andrew Fraknoi of ASP
- Venus Nomenclature Table
- Magellan Image Browser
- maps of Venus, Mars and the Moon
Open Issues & Big Questions
- There is some evidence of spreading and folding on Venus' surface and
of recent volcanic flows.
But there is no evidence of plate tectonics
as seen on Earth. Is this a result of the higher surface temperature?
- The greenhouse effect is much stronger on Venus than Earth because of Venus'
dense carbon dioxide atmosphere. But why did Venus evolve so differently
- Is Venus more volcanically active than it has been? Venus is known to
have more then 1600 volcano's and a recent study results show evidence of
sulfur dioxide into the atmosphere of Venus. This suggests volcanic activity
has increased the sulfur dioxide level in the upper atmosphere.
- What are the mysterious ultraviolet markings on the clouds? While looking at the cloud layer of Venus does not reveal much, interesting markings emerge when the looking at the clouds in ultravoilet light. These markings absorb half of the solar energy received by the plant, how these markings are made and why the high power absorption is a mystery.