Find us on Google+

Venus

Venus-imaged-by-Magellan[1]

Venus

 

Diameter: 12,104 km
Distance from Sun: 108,200,000 km
Surface area: 460,234,317 km²
Length of day: 116d 18h 0m
Gravity: 8.87 m/s²
Circumference: 38,024 km
Mass: 4.867E24 kg (0.815 Earth mass)
Length of Year: 224.70 Earth Days
Surface temp: 462 C

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%. Venus (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.

Venera 9 surface photo

Venera 9 surface photo

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 is now in orbit with a large variety of instruments.

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.

Because of  these similarities, it was thought that below its dense clouds Venus  might  be very Earthlike and might even have life. But, unfortunately, more  detailed study of Venus reveals that in many important  ways it is  radically different from Earth.  It may be the least hospitable place for life  in the solar system.

Venus from Galileo

Venus in visible  light from Galileo

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 sulfuric 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’s  surface is  actually hotter than Mercury’s despite being  nearly twice as far from the Sun.

Small image of Venus

Venus in ultra-violet light

There are strong (350 kph)  winds at the cloud tops but winds at the surface are very slow, no more  than a few kilometers per hour. 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.

Lava flow on Venus

Sif Mons (Magellan radar)

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’s 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.

Coronae on Venus

Coronae
pancakes venus
Pancake volcanoes

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 one was in 1882,  the  next one is in 2012 but after than 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.

 

 

by
Venus

by with no comments yet.

Leave a Reply

Your email address will not be published. Required fields are marked *