Revealing Venus

The second planet from the Sun is our nearest planetary neighbor. Since its orbit is inside that of the Earth, it is seen from the Earth both in the evening and morning skies at different times. Its surface is completely shrouded with highly reflective clouds, leading to its brilliant appearance in the sky. Venus has enchanted most civilizations- at least thirty different names for Venus in different cultures are known (from "Venus Revealed" by David Grinspoon). The Maya civilization in Central America used Venus as an accurate calendar.

Click here for notes on changes in the Cycle Times of Venus within recorded history.

The brightness of Venus and its periodic proximity to the Earth have made Venus an easy target for advances in astronomical observations. Venus has been the object of telescopic observations from the beginning. The appearance of the phases of Venus by Galileo is a milestone in the modern understanding of the solar system. Indeed, Venus has played a very crucial role in many modern advances in science. Early measurements of the speed of light were derived from observations of the transit of Venus across the solar disk as seen from the earth. Venus was also the first solar system object from which radar signals were first bounced off in late 1960's. First radar observations of another planet from an orbiting platform were made at Venus by the Venera 15 spacecraft and were followed by Pioneer Venus Orbiter and subsequently by Magellan.

The launch of Mariner 2 spacecraft in 1962 started the modern era of Venus exploration by spacecraft. Since then Venus has been observed by reconnaissance spacecraft Mariner 5 , Mariner 10 , and by the Soviet "Mother Spacecraft" Veneras 8, 9, 10. Venus has also been investigated as a target of opportunity by spacecraft designed primarily to explore another object by Mariner 10 (Mercury), by the VeGa 1 and VeGa 2 (Comet Halley), and Galileo (Jupiter and its moons). More intense investigation of Venus has been carried out by orbiters (Veneras 11, 12, 13, 14, 15, 15, Pioneer and Magellan), entry probes (Venera 4, 5, 6, and Pioneer Venus Small Probes and one Large Probe) as well as landers (Venera 6, 7, 8, 9, 10, 11, 12, 13, and 14), and even balloons (VeGa 1 and VeGa 2). The most recent observations of Venus are from the Galileo spacecraft which flew past Venus in February 1990 on its roundabout journey to Jupiter.

While these space missions have changed our view of Venus substantially and enhanced our knowledge, some of the fundamental questions about Venus and its atmosphere remain unanswered. The most frustrating one to an atmospheric scientist is the explanation of the rapid rotation of its atmosphere, many times faster than the underlying planet. To a geologist, the major question is how does Venus lose its heat? For a chemist, the burning question is whether the surface of Venus is in equilibrium with its atmosphere.

Atmosphere of Venus

Of all the terrestrial planets, Venus has the thickest atmosphere. With its slow rotation rate about its spin axis (243.16 days), Venus is in a class its own with only Titan, the atmosphere bearing moon of Saturn as its only companion (rotation rate of about 16 days). With no oceans to vary the surface heating, no tilt to its rotation axis, a nearly circular orbit around the Sun, no large scale topography, and a nearly uniform, global cloud cover, the atmosphere of Venus would seem to be easy to understand in terms of the effect of insolation- no seasons, no hydrologic cycle. Thus the early efforts to model the state of the Venus atmosphere suggested that the winds should blow from the day-side to the night side, and that the day-night temperature difference could be large indeed. Ground based and spacecraft observations tell us otherwise - the winds blow essentially in the same direction as the rotating planet at all observed latitudes and at all
altitudes to about 100 km! It is only in the atmosphere above 100 km that the winds blow from the day-side to the night-side. Below 100 km the winds blow predominantly from east to west with a slight poleward component. Further, the east winds and the poleward component generally increase with latitude to about 45 degrees. Polewards of this latitude in both the hemispheres, the east-west (zonal) and the north-south (meridional) winds decrease towards the pole. There is thus a peak in the angular speed of the atmosphere in two bands about mid-way between the equator of Venus and its poles- the equivalent of the terrestrial jet stream.


Click here to see larger image
This global structure of the atmospheric motion organizes the Venus atmosphere
in the form of two giant hemispheric vortices, one in each hemisphere centered over the pole.

 

VESAT - A Discovery Mission to Venus

To investigate the cause of the superrotation of the atmosphere of Venus and to explore the interplay between the atmospheric chemistry and the Venus surface, a Discovery Mission has been proposed to NASA. Click here for more information on the Venus Environmental Satellite.

 


  Here are links that provide more information about Venus:

For more information on the Solar System and other planets, visit the following sites: