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At first glance, if Earth had a twin,
it would be Venus. The two planets are similar in size,
mass, composition, and distance from the Sun. But there
the similarities end. Venus has no ocean. Venus is covered
by thick, rapidly spinning clouds that trap surface
heat, creating a scorched greenhouse-like world with
temperatures hot enough to melt lead and pressure so
intense that standing on Venus would feel like the pressure
felt 900 meters deep in Earth's oceans. These clouds
reflect sunlight in addition to trapping heat. Because
Venus reflects so much sunlight, it is usually the brightest
planet in the sky.
The atmosphere consists mainly of carbon
dioxide (the same gas that produces fizzy sodas), droplets
of sulfuric acid, and virtually no water vapor - not
a great place for people or plants! In addition, the
thick atmosphere allows the Sun's heat in but does not
allow it to escape, resulting in surface temperatures
over 450 ÁC, hotter than the surface of the planet Mercury,
which is closest to the Sun. The high density of the
atmosphere results in a surface pressure 90 times that
of Earth, which is why probes that have landed on Venus
have only survived several hours before being crushed
by the incredible pressure. In the upper layers, the
clouds move faster than hurricane- force winds on Earth.
Venus sluggishly rotates on its axis once
every 243 Earth days, while it orbits the Sun every
225 days - its day is longer than its year! Besides
that, Venus rotates retrograde, or "backwards," spinning
in the opposite direction of its orbit around the Sun.
From its surface, the Sun would seem to rise in the
west and set in the east.
Earth and Venus are similar in density
and chemical compositions, and both have relatively
young surfaces, with Venus appearing to have been completely
resurfaced 300 to 500 million years ago.
The surface of Venus is covered by about
20 percent lowland plains, 70 percent rolling uplands,
and 10 percent highlands. Volcanism, impacts, and deformation
of the crust have shaped the surface. No direct evidence
of currently active volcanoes has been found, although
large variations of sulfur dioxide in the atmosphere
lead some scientists to suspect that volcanoes may be
active.
Although no rainfall, oceans, or strong
winds exist to erode surface features, some weathering
and erosion does occur. The surface is brushed by gentle
winds, no stronger than a few kilometers per hour, enough
to move grains of sand, and radar images of the surface
show wind streaks and sand dunes. In addition, the corrosive
atmosphere probably chemically alters rocks. Impact
cratering is also affected by the dense atmosphere:
craters smaller than 1.5 to 2 km across do not exist
on Venus, largely because small meteors burn up in Venus?
dense atmosphere before they can reach the surface.
More than 1,000 volcanoes or volcanic
centers larger than 20 km in diameter dot the surface
of Venus. There may be close to a million volcanic centers
that are over 1 km in diameter. Much of the surface
is covered by vast lava flows. In the north, an elevated
region named Ishtar Terra is a lava-filled basin larger
than the continental United States. Near the equator,
the Aphrodite Terra highlands, more than half the size
of Africa, extend for almost 10,000 km. Volcanic flows
have also produced long, sinuous chan-nels extending
for hundreds of kilometers.With few exceptions, features
on Venus are named for accomplished women from all of
Earth's cultures.
Venus' interior is probably very similar
to that of Earth, containing an iron core about 3,000
km in radius and a molten rocky mantle covering the
majority of the planet. Recent results from the Magellan
spacecraft suggest that Venus' crust is stronger and
thicker than had previously been thought. Venus has
no satellites and no intrinsic magnetic field, but the
solar wind rushing by Venus creates a pseudo-field around
the planet.
Related Links:
Source: NASA
Last Updated : 08.20.2003
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Distance from the Sun:
(Semimajor axis of orbit)
108,208,930 km
0.72333199 A.U.
Radius:
6,051.8 km
(0.9488 of Earth's radius)
Volume:
0.88 (Earth = 1)
Mass:
4.8690 x 1027 g
Density:
5.24 gm/cm3
Surface Gravity:
887 cm/s2
Escape Velocity:
10.36 km/s (at equator)
Sidereal Rotation Period:
-243.0187 days (retrograde)
Sidereal Orbit Period:
0.61519726 sidereal years
Mean Orbit Velocity:
35.0214 km/s
Orbit Eccentricity:
0.00677323
Orbit Inclination:
3.39471 degrees
Equatorial Inclination:
177.3 degrees
Mean Surface Temperature:
730 K
Major Atmospheric Constituents:
CO2, N2
Natural Satellites:
None
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