NEEP602 Course Notes (Fall 1996)
Resources from Space


The Bringer of Peace

Venus Facts

Venus's orbit is the most nearly circular of that of any planet, with an eccentricity (0.007) less than 1%
  • Venus "quasi" facts
    • surface may be as little as 500 My old from crater counts per unit area & random distribution of craters
    • no cold (trap) region in the present atmosphere to condense water and prevent its loss (especially hydrogen from dissociation of water) into space (escape velocity Venus 10.4 km/sec, Earth 11.2km/sec), hence very little water now
    • absence of water may make similar rocks stronger than on Earth by factor of 10
    • crude estimate of heat flow, if like Earth, 1-1.5 cal/cm2/sec mainly from radio active decay but no plate tectonics (unlike Earth, unimodal topography vs elevation) to make escape of heat easy.
    • no life now

    The planet is so named probably because it is the brightest of the planets known to the ancients.

  • Venus has been known since prehistoric times. It is the brightest object in the sky except for the Sun and the Moon.

  • Since Venus is an inferior planet, it shows phases when viewed with a telescope from the perspective of the 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. Most recently, the orbiting US spacecraft Magellan produced detailed maps of Venus's surface using radar.

  • Venus's rotation is somewhat unusual in that it is both very slow (243 Earth days per Venus day, slightly longer than Venus's year) and retrograde. In addition, the periods of Venus's 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.

  • 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.

  • The pressure of Venus's 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 surface (picture 2). This dense atmosphere produces a run-away greenhouse effect that raises Venus's 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.

  • There are strong (350 kph) winds at the cloud tops (picture 6) 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. We may learn a lot about Earth by learning why the basically similar Venus turned out so differently.

  • Most of Venus's 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 (picture 3). Recently announced findings indicate that Venus is still volcanically active, but only in a few hot spots (picture 4); for the most part it has been geologically rather quiet for the past few hundred million years.

  • There are no small craters on Venus because small meteors burn up in Venus's dense atmosphere before reaching the surface. Craters on Venus seem to come in bunches (picture 11) indicating that large meteors that do reach the surface usually break up in the atmosphere.

  • The oldest terrains on Venus seem to be <500million years old. Extensive volcanism at that time wiped out the earlier surface including any large craters from early in Venus's history.

  • Magellan's images show a wide variety of interesting and unique features including pancake volcanoes which seem to be eruptions of very thick lava (picture 8) and coronae which seem to be collapsed domes over large magma chambers (picture 9).

  • The interior of Venus is probably very similar to that of Earth: an iron core about 3000 km in radius, a largely molten rocky mantle comprising the majority of the planet. Recent results from the Magellan gravity data indicate that Venus's lithosphere (crust and upper mantle) is stronger and thicker than had previously been assumed. Unlike Earth, convection in the defrming lower mantle produces stress on the surface which is relieved in many relatively small regions eposodically instead more continually at plate boundaries as is the case on Earth.

  • Venus has no magnetic field, perhaps because of its slow rotation.

  • Venus is usually visible with the naked eye. Mike Harvey's planet finder charts show the current position of Venus (and the other planets) in the sky.


    1. (above) False color high-res image a whole hemisphere 342k gif; 3000k gif

    2. Visible light view from Galileo 73k gif

    3. Sif Mons 156k gif; 270k jpg

    4. Recent Volcanism 123k gif; 22k jpg

    5. Large Impact Crater 131k gif; 495k jpg

    6. Image from Pioneer Venus 15k jpg

    7. Gula Mons and Cunitz crater 250k gif; 178k jpg

    8. 7 pancake volcanoes, alpha region 227k gif; 327k jpg

    9. Pandora Corona, Lada Terra 42.5 deg S 6 lon 177k gif; 186k jpg

    10. Vires-Akka Chasma, Denitsa Region 130k gif; 337k jpg
    11. Crater Farm, Lavinia Region, small 107k gif; 147k jpg
    12. Volcano, 3 mile diameter, paragon chasma, 9.4S by 247.5 long 282k gif; 72k jpg
    13. Golubkina crater, 60.5 Deg N, 287.2 Long (computer generated Perspective) 107k gif; 149k jpg
    14. Alpha Regio, showing hills and craters 237k gif

    15. UV image from HST (false color) 23k jpg; 99k gif; 1200k tiff

    16. New Magellan global mosaics html

    17. Surface photographs from the Soviet Venera 9 and 10 spacecraft

    18. NASA PDS Magellan Image Browser html
    19. ... more Venus images


    1. Venus animation 1542K fli; 1239K pics; 405K quicktime; 444K B&W pics
    2. Venus Globe Animation 303k mpeg
    3. Earth/Venus Rotation Movie 1000k AVI
    4. Magellan - Mapping the planet Venus 10000k AVI
    5. Flight over Western Atla Regio 7000k AVI; (caption)
    6. Flight over Artemis 11000k AVI; 23000k AVI; (caption)
    7. Flight over Alpha Regio 8000k AVI; (caption)
    8. Flight over Western Eistla Regio - 3300k AVI; 7600k AVI; 15000k AVI; (caption)
    9. A dramatic view the the moon with Venus in the distance 82k mpeg

    More about Venus

    Open Issues

    • There is some evidence of spreading and folding on Venus's 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's dense carbon dioxide atmosphere. But why did Venus evolve so differently from Earth?

    Contents ... Sun ... Mercury ... Venus ... Earth ... Data Host

    Bill Arnett; original source: 1995 August 12
    Revised for 602/376 by R. P. Meyer, February 19, 1996
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