Venus Facts
-Venus has a some what unusual rotation- slow, 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.
-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
-Venus has no magnetic field, perhaps because of its slow rotation. Venus has no satellites.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.
-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 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 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.
-The first spacecraft to visit Venus was in1962.
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 is the second planet from the Sun, with a nearly circular orbit having an average
radius of 0.7 A.U. This gives it an orbital period of 225 days. Venus is peculiar in that its
rotation is retrograde (in the opposite sense of the Earth and all other planets except
Uranus) and because it is very slow: a day on Venus corresponds to 243 Earth days. At
present, we have no solid explanation for why this is so. The most plausible theories invoke
the collision of two large masses to form Venus in just such a way to cancel most of the
rotation for the two masses. Like Mercury, but unlike the other planets, Venus has no
moons.
The radius of Venus is almost exactly that of the Earth. Its average density is 5.2 g/cc,
which is slightly less than that of the Earth or Mercury, but suggests a dense iron core and
internal structure similar to that of the Earth. Venus has an extremely weak magnetic field,
but that may be a consequence of its having such a slow rotational velocity.
Venus is always covered by a thick layer of clouds that make it impossible to see the surface
for light in the visible part of the spectrum. Light at radar wavelengths penetrates the
cloud deck and allows us to study the surface. A comparison of the motion of the surface
with that of the upper clouds indicates that while the surface takes about 8 months to
rotate, the clouds rotate all the way around the planet in about 4 days. This indicates that
there are very high velocity winds in the upper part of the Venusian atmosphere.
Volcanos and Lava Flows
There is strong evidence that volcanoes have erupted on Venus in the geologically recent
past, and strong indirect evidence from observations like changing chemical composition of
the atmosphere and the detection of lightning in certain regions that volcanoes are
presently active on Venus, though we do not yet have direct proof. (Here is a map of
volcanic structures on Venus.) One piece of evidence for recent volcanic activity is the
presence in many regions of features that look like relatively new lava flows. The two
images shown below illustrates a volcano about 3 miles in diameter near Paragon Chasma
(left) and an image of apparent recent lava flows in the Sif Mons region.
A Field of Craters
The Largest Crater (Ref)
High Velocity Winds
A comparison of surface and upper cloud velocities indicates that there are winds in the
upper part of the Venusian atmosphere with velocities as large as 300 km/hour. These
winds are comparable in speed to jetstreams in the Earth's atmosphere, but extend over
much larger regions in the case of Venus. It is not fully understood why these winds have
such high velocities.
Absence of Water Vapor
The clouds contain little water vapor, and there is little evidence for water in any form on
Venus. It is speculated that the absence of water is because most water that may have
initially been on Venus made its way to the upper atmosphere, where it was broken down
by sunlight and interactions with cosmic rays and the solar wind into oxygen and
hydrogen, which was then lost to interplanetary space
The atmosphere of Venus is composed of about 96% carbon dioxide, with most of the
remainder being nitrogen. The atmosphere appears to be relatively clear until the cloud
deck starts about 50 km above the surface. As noted in the previous section, the clouds are
composed of sulphuric acid and various other corrosive compounds, and the atmosphere
contains little water.
The pressure of the atmosphere is about 90 times that of the Earth at the surface, and the
surface temperatures on Venus are around 500 degrees Celsius, exceeding that of Mercury
and hot enough to melt soft metals. Calculations indicate that for the temperatures to be so
high there must be a mechanism in the Venusian atmosphere that traps solar radiation
very effectively. As we will see in the next section, these rather remarkable properties of the
atmosphere are thought to be a consequence of a runaway greenhouse effect.
There are high-velocity winds in the upper atmosphere, but the atmosphere below the
cloud deck appears to be relatively stagnant, with only very weak winds blowing at the
surface. Convection driven by differential solar heating should give rise to winds of only a
few meters per second, so the high velocity upper level winds, and the contrasting
stagnation of the lower atmosphere, are not well understood.