Venus

Venus is the second planet from the Sun.

It is named after the Roman goddess of
love and beauty. As the second-brightest
natural object in the night sky after the
Moon, Venus can cast shadows and can
be, on rare occasion, visible to the naked
eye in broad daylight.[15][16] Venus lies
within Earth's orbit, and so never appears
to venture far from the Sun, either setting
in the west just after dusk or rising in the
east a bit before dawn. Venus orbits the
Sun every 224.7 Earth days.[17] With a
rotation period of 243 Earth days, it takes
longer to rotate about its axis than any
other planet in the Solar System and does
so in the opposite direction to all but
Uranus (meaning the Sun rises in the west
and sets in the east).[18] Venus does not
have any moons, a distinction it shares
only with Mercury among planets in the
Solar System.[19]
 Venus

A real-color image taken by Mariner 10 in

newly processed view (8 June 2020); the
surface is obscured by thick sulfuric acid
clouds

Designations

Pronunciation /ˈviːnəs/ ( listen)

Adjectives Venusian /vɪˈnjuːziən,

-ʒən/,[1] rarely
Cytherean /sɪθəˈriːən/
 [see][2] or Venerean /
Venerian /vɪˈnɪəriən/[3]

Orbital characteristics[5][7]

Epoch J2000

Aphelion 0.728 213 AU

108,939,000 km

Perihelion 0.718 440 AU

107,477,000 km
Semi-major axis 0.723 332 AU
108,208,000 km

Eccentricity 0.006772[4]
Orbital period 224.701 d[5]
0.615 198 yr
1.92 Venus solar day
Synodic period 583.92 days[5]
Average orbital speed 35.02 km/s

Mean anomaly 50.115°

Inclination 3.394 58° to ecliptic

3.86° to Sun's equator
2.19° to invariable
plane[6]
Longitude of 76.680°[4]
ascending node
Argument of 54.884°
perihelion
Satellites None

Physical characteristics
Mean radius 6,051.8 ± 1.0 km[8]
0.9499 Earths
Flattening 0[8]
Surface area 4.6023 × 108 km2
0.902 Earths

Volume 9.2843 × 1011 km3

0.866 Earths

Mass 4.8675 × 1024 kg[9]

0.815 Earths
Mean density 5.243 g/cm3
Surface gravity 8.87 m/s2
0.904 g
Escape velocity 10.36 km/s
(6.44 mi/s)[10]
Sidereal rotation −243.025 d
period
(retrograde)[5]
Equatorial 6.52 km/h (1.81 m/s)
rotation velocity
Axial tilt 2.64° (for retrograde
rotation)
177.36° (to
orbit)[5][note 1]

North pole right  18h 11m 2s

ascension
272.76°[11]

North pole 67.16°
declination
Albedo 0.689 (geometric)[12]
0.76 (Bond)[13]

Surface temp. min mean max

Kelvin 737 K[5]
Celsius 464 °C
Fahrenheit 867 °F
Apparent magnitude −4.92 to −2.98[14]
Angular diameter 9.7″–66.0″[5]
 Atmosphere[5]
Surface pressure 92 bar (9.2 MPa)
91 atm

Composition by 96.5% carbon dioxide

volume 3.5% nitrogen
0.015% sulfur dioxide
0.0070% argon
0.0020% water vapour
0.0017% carbon
monoxide
0.0012% helium
0.0007% neon
Trace carbonyl sulfide
Trace hydrogen
chloride
 Trace hydrogen
fluoride
1. Defining the rotation as retrograde, as
done by NASA space missions and the
USGS, puts Ishtar Terra in the northern
hemisphere and makes the axial tilt 2.64°.
Following the right-hand rule for prograde
rotation puts Ishtar Terra in the southern
hemisphere and makes the axial tilt
177.36°.

Venus is a terrestrial planet and is

sometimes called Earth's "sister planet"
because of their similar size, mass,
proximity to the Sun, and bulk
composition. It is radically different from
Earth in other respects. It has the densest
atmosphere of the four terrestrial planets,
consisting of more than 96% carbon
dioxide. The atmospheric pressure at the
planet's surface is 92 times that of Earth,
or roughly the pressure found 900 m
(3,000 ft) underwater on Earth. Venus is by
far the hottest planet in the Solar System,
with a mean surface temperature of 735 K
(462 °C; 863 °F), even though Mercury is
closer to the Sun. Venus is shrouded by an
opaque layer of highly reflective clouds of
sulfuric acid, preventing its surface from
being seen from space in visible light. It
may have had water oceans in the
past,[20][21] but these would have vaporized
as the temperature rose due to a runaway
greenhouse effect.[22] The water has
probably photodissociated, and the free
hydrogen has been swept into
interplanetary space by the solar wind
because of the lack of a planetary
magnetic field.[23] Venus's surface is a dry
desertscape interspersed with slab-like
rocks and is periodically resurfaced by
volcanism.

As one of the brightest objects in the sky,

Venus has been a major fixture in human
culture for as long as records have
existed. It has been made sacred to gods
of many cultures, and has been a prime
inspiration for writers and poets as the
morning star and evening star. Venus was
the first planet to have its motions plotted
across the sky, as early as the second
millennium BC.[24]

As the planet with the closest approach to

Earth, Venus has been a prime target for
early interplanetary exploration. It was the
first planet beyond Earth visited by a
spacecraft (Mariner 2 in 1962), and the
first to be successfully landed on (by
Venera 7 in 1970). Venus's thick clouds
render observation of its surface
impossible in visible light, and the first
detailed maps did not emerge until the
arrival of the Magellan orbiter in 1991.
Plans have been proposed for rovers or
more complex missions, but they are
hindered by Venus's hostile surface
conditions.

In January 2020, astronomers reported

evidence that suggests that Venus is
currently volcanically active.[25][26]

Physical characteristics
Venus is one of the four terrestrial planets
in the Solar System, meaning that it is a
rocky body like Earth. It is similar to Earth
in size and mass, and is often described
as Earth's "sister" or "twin".[27] The
diameter of Venus is 12,103.6 km
(7,520.8 mi)—only 638.4 km (396.7 mi)
less than Earth's—and its mass is 81.5% of
Earth's. Conditions on the Venusian
surface differ radically from those on Earth
because its dense atmosphere is 96.5%
carbon dioxide, with most of the remaining
3.5% being nitrogen.[28]

Geography

Size comparison showing a representation of Venus

(using a false-colour, radar-based image of the
surface) and Earth
 Planet Venus - old vs new processed views (Mariner
10; 1974/2020)

The topographic Globe of Venus

The Radar Globe of Venus

The Venusian surface was a subject of

speculation until some of its secrets were
revealed by planetary science in the 20th
century. Venera landers in 1975 and 1982
returned images of a surface covered in
sediment and relatively angular rocks.[29]
The surface was mapped in detail by
Magellan in 1990–91. The ground shows
evidence of extensive volcanism, and the
sulfur in the atmosphere may indicate that
there have been recent eruptions.[30][31]

About 80% of the Venusian surface is

covered by smooth, volcanic plains,
consisting of 70% plains with wrinkle
ridges and 10% smooth or lobate
plains.[32] Two highland "continents" make
up the rest of its surface area, one lying in
the planet's northern hemisphere and the
other just south of the equator. The
northern continent is called Ishtar Terra
after Ishtar, the Babylonian goddess of
love, and is about the size of Australia.
Maxwell Montes, the highest mountain on
Venus, lies on Ishtar Terra. Its peak is
11 km (7 mi) above the Venusian average
surface elevation.[33] The southern
continent is called Aphrodite Terra, after
the Greek goddess of love, and is the
larger of the two highland regions at
roughly the size of South America. A
network of fractures and faults covers
much of this area.[34]

The absence of evidence of lava flow

accompanying any of the visible calderas
remains an enigma. The planet has few
impact craters, demonstrating that the
surface is relatively young, approximately
300–600 million years old.[35][36] Venus
has some unique surface features in
addition to the impact craters, mountains,
and valleys commonly found on rocky
planets. Among these are flat-topped
volcanic features called "farra", which look
somewhat like pancakes and range in size
from 20 to 50 km (12 to 31 mi) across, and
from 100 to 1,000 m (330 to 3,280 ft) high;
radial, star-like fracture systems called
"novae"; features with both radial and
concentric fractures resembling spider
webs, known as "arachnoids"; and
"coronae", circular rings of fractures
sometimes surrounded by a depression.
These features are volcanic in origin.[37]
Most Venusian surface features are
named after historical and mythological
women.[38] Exceptions are Maxwell
Montes, named after James Clerk
Maxwell, and highland regions Alpha
Regio, Beta Regio, and Ovda Regio. The
last three features were named before the
current system was adopted by the
International Astronomical Union, the body
which oversees planetary
nomenclature.[39]

The longitude of physical features on

Venus are expressed relative to its prime
meridian. The original prime meridian
passed through the radar-bright spot at the
centre of the oval feature Eve, located
south of Alpha Regio.[40] After the Venera
missions were completed, the prime
meridian was redefined to pass through
the central peak in the crater
Ariadne.[41][42]

Surface geology

False-colour radar map of Maat Mons with a vertical

exaggeration of 22.5
Much of the Venusian surface appears to
have been shaped by volcanic activity.
Venus has several times as many
volcanoes as Earth, and it has 167 large
volcanoes that are over 100 km (60 mi)
across. The only volcanic complex of this
size on Earth is the Big Island of
Hawaii.[37]:154 This is not because Venus is
more volcanically active than Earth, but
because its crust is older. Earth's oceanic
crust is continually recycled by subduction
at the boundaries of tectonic plates, and
has an average age of about 100 million
years,[43] whereas the Venusian surface is
estimated to be 300–600 million years
old.[35][37]
Several lines of evidence point to ongoing
volcanic activity on Venus. Sulphur dioxide
concentrations in the atmosphere dropped
by a factor of 10 between 1978 and 1986,
jumped in 2006, and again declined 10-
fold.[44] This may mean that levels had
been boosted several times by large
volcanic eruptions.[45][46] It has also been
suggested that Venusian lightning
(discussed below) could originate from
volcanic activity (i.e. volcanic lightning). In
January 2020, astronomers reported
evidence that suggests that Venus is
currently volcanically active.[25][26]
In 2008 and 2009, the first direct evidence
for ongoing volcanism was observed by
Venus Express, in the form of four transient
localized infrared hot spots within the rift
zone Ganis Chasma,[47][n 1] near the shield
volcano Maat Mons. Three of the spots
were observed in more than one
successive orbit. These spots are thought
to represent lava freshly released by
volcanic eruptions.[48][49] The actual
temperatures are not known, because the
size of the hot spots could not be
measured, but are likely to have been in
the 800–1,100 K (527–827 °C; 980–
1,520 °F) range, relative to a normal
temperature of 740 K (467 °C; 872 °F).[50]
Impact craters on the surface of Venus (false-colour
image reconstructed from radar data)

Almost a thousand impact craters on

Venus are evenly distributed across its
surface. On other cratered bodies, such as
Earth and the Moon, craters show a range
of states of degradation. On the Moon,
degradation is caused by subsequent
impacts, whereas on Earth it is caused by
wind and rain erosion. On Venus, about
85% of the craters are in pristine condition.
The number of craters, together with their
well-preserved condition, indicates the
planet underwent a global resurfacing
event about 300–600 million years
ago,[35][36] followed by a decay in
volcanism.[51] Whereas Earth's crust is in
continuous motion, Venus is thought to be
unable to sustain such a process. Without
plate tectonics to dissipate heat from its
mantle, Venus instead undergoes a
cyclical process in which mantle
temperatures rise until they reach a critical
level that weakens the crust. Then, over a
period of about 100 million years,
subduction occurs on an enormous scale,
completely recycling the crust.[37]
Venusian craters range from 3 to 280 km
(2 to 174 mi) in diameter. No craters are
smaller than 3 km, because of the effects
of the dense atmosphere on incoming
objects. Objects with less than a certain
kinetic energy are slowed so much by the
atmosphere that they do not create an
impact crater.[52] Incoming projectiles less
than 50 m (160 ft) in diameter will
fragment and burn up in the atmosphere
before reaching the ground.[53]

Internal structure
The internal structure of Venus – the crust (outer

layer), the mantle (middle layer) and the core (yellow

inner layer)

Without seismic data or knowledge of its

moment of inertia, little direct information
is available about the internal structure
and geochemistry of Venus.[54] The
similarity in size and density between
Venus and Earth suggests they share a
similar internal structure: a core, mantle,
and crust. Like that of Earth, the Venusian
core is at least partially liquid because the
two planets have been cooling at about
the same rate.[55] The slightly smaller size
of Venus means pressures are 24% lower
in its deep interior than Earth's.[56] The
principal difference between the two
planets is the lack of evidence for plate
tectonics on Venus, possibly because its
crust is too strong to subduct without
water to make it less viscous. This results
in reduced heat loss from the planet,
preventing it from cooling and providing a
likely explanation for its lack of an
internally generated magnetic field.[57]
Instead, Venus may lose its internal heat in
periodic major resurfacing events.[35]

Atmosphere and climate

Cloud structure in
the Venusian
atmosphere in
2018, revealed by
observations in
the two ultraviolet
bands by Akatsuki
 False-color global
radar view of
Venus (without
the clouds) from
Magellan between
1990 and 1994

Venus has an extremely dense

atmosphere composed of 96.5% carbon
dioxide, 3.5% nitrogen, and traces of other
gases including sulfur dioxide.[58] The
mass of its atmosphere is 93 times that of
Earth's, whereas the pressure at its surface
is about 92 times that at Earth's—a
pressure equivalent to that at a depth of
nearly 1 km (5⁄8 mi) under Earth's oceans.
The density at the surface is 65 kg/m3,
6.5% that of water or 50 times as dense as
Earth's atmosphere at 293 K (20 °C; 68 °F)
at sea level. The CO2-rich atmosphere
generates the strongest greenhouse effect
in the Solar System, creating surface
temperatures of at least 735 K (462 °C;
864 °F).[17][59] This makes Venus's surface
hotter than Mercury's, which has a
minimum surface temperature of 53 K
(−220 °C; −364 °F) and maximum surface
temperature of 700 K (427 °C;
801 °F),[60][61] even though Venus is nearly
twice Mercury's distance from the Sun and
thus receives only 25% of Mercury's solar
irradiance. This temperature is higher than
that used for sterilization.

Studies have suggested that billions of

years ago, Venus's atmosphere was much
more like the one surrounding Earth, and
that there may have been substantial
quantities of liquid water on the surface,
but after a period of 600 million to several
billion years,[62] a runaway greenhouse
effect was caused by the evaporation of
that original water, which generated a
critical level of greenhouse gases in its
atmosphere.[63] Although the surface
conditions on Venus are no longer
hospitable to any Earth-like life that may
have formed before this event, there is
speculation on the possibility that life
exists in the upper cloud layers of Venus,
50 km (30 mi) up from the surface, where
the temperature ranges between 303 and
353 K (30 and 80 °C; 86 and 176 °F) but
the environment is acidic.[64][65][66]

Thermal inertia and the transfer of heat by

winds in the lower atmosphere mean that
the temperature of Venus's surface does
not vary significantly between the planet's
two hemispheres, those facing and not
facing the Sun, despite Venus's extremely
slow rotation. Winds at the surface are
slow, moving at a few kilometres per hour,
but because of the high density of the
atmosphere at the surface, they exert a
significant amount of force against
obstructions, and transport dust and small
stones across the surface. This alone
would make it difficult for a human to walk
through, even without the heat, pressure,
and lack of oxygen.[67]

Above the dense CO2 layer are thick clouds

consisting mainly of sulfuric acid, which is
formed by sulfur dioxide and water
through a chemical reaction resulting in
sulfuric acid hydrate. Additionally, the
atmosphere consists of approximately 1%
ferric chloride.[68][69] Other possible
constituents of the cloud particles are
ferric sulfate, aluminium chloride and
phosphoric anhydride. Clouds at different
levels have different compositions and
particle size distributions.[68] These clouds
reflect and scatter about 90% of the
sunlight that falls on them back into
space, and prevent visual observation of
Venus's surface. The permanent cloud
cover means that although Venus is closer
than Earth to the Sun, it receives less
sunlight on the ground. Strong 300 km/h
(185 mph) winds at the cloud tops go
around Venus about every four to five
Earth days.[70] Winds on Venus move at up
to 60 times the speed of its rotation,
whereas Earth's fastest winds are only 10–
20% rotation speed.[71]

The surface of Venus is effectively

isothermal; it retains a constant
temperature not only between the two
hemispheres but between the equator and
the poles.[5][72] Venus's minute axial tilt—
less than 3°, compared to 23° on Earth—
also minimises seasonal temperature
variation.[73] Altitude is one of the few
factors that affect Venusian temperature.
The highest point on Venus, Maxwell
Montes, is therefore the coolest point on
Venus, with a temperature of about 655 K
(380 °C; 715 °F) and an atmospheric
pressure of about 4.5 MPa (45 bar).[74][75]
In 1995, the Magellan spacecraft imaged a
highly reflective substance at the tops of
the highest mountain peaks that bore a
strong resemblance to terrestrial snow.
This substance likely formed from a
similar process to snow, albeit at a far
higher temperature. Too volatile to
condense on the surface, it rose in
gaseous form to higher elevations, where
it is cooler and could precipitate. The
identity of this substance is not known
with certainty, but speculation has ranged
from elemental tellurium to lead sulfide
(galena).[76]
Although Venus has no seasons as such,
in 2019 astronomers identified a cyclical
variation in sunlight absorption by the
atmosphere, possibly caused by opaque,
absorbing particles suspended in the
upper clouds. The variation causes
observed changes in the speed of Venus's
zonal winds, and appears to rise and fall in
time with the Sun's 11-year sunspot
cycle.[77]

The existence of lightning in the

atmosphere of Venus has been
controversial[78] since the first suspected
bursts were detected by the Soviet Venera
probes[79][80][81] In 2006–07, Venus Express
clearly detected whistler mode waves, the
signatures of lightning. Their intermittent
appearance indicates a pattern associated
with weather activity. According to these
measurements, the lightning rate is at
least half of that on Earth,[82] however
other instruments have not detected
lightning at all.[78] The origin of any
lightning remains unclear, but could
originate from the clouds or volcanoes.

In 2007, Venus Express discovered that a

huge double atmospheric vortex exists at
the south pole.[83][84] Venus Express also
discovered, in 2011, that an ozone layer
exists high in the atmosphere of Venus.[85]
On 29 January 2013, ESA scientists
reported that the ionosphere of Venus
streams outwards in a manner similar to
"the ion tail seen streaming from a comet
under similar conditions."[86][87]

In December 2015, and to a lesser extent

in April and May 2016, researchers
working on Japan's Akatsuki mission
observed bow shapes in the atmosphere
of Venus. This was considered direct
evidence of the existence of perhaps the
largest stationary gravity waves in the
solar system.[88][89][90]

Atmospheric composition
 Absorption spectrum of a
simple gas mixture
corresponding to Earth's
atmosphere

The composition of the

atmosphere of Venus based on
HITRAN data[91] created using
HITRAN on the Web system.[92]

Green colour – water vapour, red – carbon dioxide,

WN – wavenumber (other colours have different
 WN – wavenumber (other colours have different
meanings, lower wavelengths on the right, higher on
the left).

Magnetic field and core

In 1967, Venera 4 found Venus's magnetic

field to be much weaker than that of Earth.
This magnetic field is induced by an
interaction between the ionosphere and
the solar wind,[93][94] rather than by an
internal dynamo as in the Earth's core.
Venus's small induced magnetosphere
provides negligible protection to the
atmosphere against cosmic radiation.

The lack of an intrinsic magnetic field at

Venus was surprising, given that it is
similar to Earth in size and was expected
also to contain a dynamo at its core. A
dynamo requires three things: a
conducting liquid, rotation, and
convection. The core is thought to be
electrically conductive and, although its
rotation is often thought to be too slow,
simulations show it is adequate to
produce a dynamo.[95][96] This implies that
the dynamo is missing because of a lack
of convection in Venus's core. On Earth,
convection occurs in the liquid outer layer
of the core because the bottom of the
liquid layer is much higher in temperature
than the top. On Venus, a global
resurfacing event may have shut down
plate tectonics and led to a reduced heat
flux through the crust. This would cause
the mantle temperature to increase,
thereby reducing the heat flux out of the
core. As a result, no internal geodynamo is
available to drive a magnetic field. Instead,
the heat from the core is being used to
reheat the crust.[97]

One possibility is that Venus has no solid

inner core,[98] or that its core is not cooling,
so that the entire liquid part of the core is
at approximately the same temperature.
Another possibility is that its core has
already completely solidified. The state of
the core is highly dependent on the
concentration of sulfur, which is unknown
at present.[97]

The weak magnetosphere around Venus

means that the solar wind is interacting
directly with its outer atmosphere. Here,
ions of hydrogen and oxygen are being
created by the dissociation of neutral
molecules from ultraviolet radiation. The
solar wind then supplies energy that gives
some of these ions sufficient velocity to
escape Venus's gravity field. This erosion
process results in a steady loss of low-
mass hydrogen, helium, and oxygen ions,
whereas higher-mass molecules, such as
carbon dioxide, are more likely to be
retained. Atmospheric erosion by the solar
wind probably led to the loss of most of
Venus's water during the first billion years
after it formed.[99] The erosion has
increased the ratio of higher-mass
deuterium to lower-mass hydrogen in the
atmosphere 100 times compared to the
rest of the solar system.[100]

Orbit and rotation

Venus orbits the Sun at an average distance of about

 g
108 million kilometres (about 0.7 AU) and completes
an orbit every 224.7 days. Venus is the second planet
from the Sun and orbits the Sun approximately
1.6 times (yellow trail) in Earth's 365 days (blue trail)

Venus orbits the Sun at an average

distance of about 0.72 AU (108 million km;
67 million mi), and completes an orbit
every 224.7 days. Although all planetary
orbits are elliptical, Venus's orbit is the
closest to circular, with an eccentricity of
less than 0.01.[5] When Venus lies between
Earth and the Sun in inferior conjunction, it
makes the closest approach to Earth of
any planet at an average distance of
41 million km (25 million mi).[5] However, it
spends a large amount of its time away
from Earth, meaning that it is the closest
planet to Earth for only a minority of the
time. This means that Mercury is actually
the planet that is closest to Earth a
plurality of the time.[101] The planet
reaches inferior conjunction every
584 days, on average.[5] Because of the
decreasing eccentricity of Earth's orbit, the
minimum distances will become greater
over tens of thousands of years. From the
year 1 to 5383, there are 526 approaches
less than 40 million km; then there are
none for about 60,158 years.[102]
All the planets in the Solar System orbit
the Sun in an anticlockwise direction as
viewed from above Earth's north pole.
Most planets also rotate on their axes in
an anti-clockwise direction, but Venus
rotates clockwise in retrograde rotation
once every 243 Earth days—the slowest
rotation of any planet. Because its rotation
is so slow, Venus is very close to
spherical.[103] A Venusian sidereal day thus
lasts longer than a Venusian year (243
versus 224.7 Earth days). Venus's equator
rotates at 6.52 km/h (4.05 mph), whereas
Earth's rotates at 1,674.4 km/h
(1,040.4 mph).[107][108] Venus's rotation
has slowed in the 16 years between the
Magellan spacecraft and Venus Express
visits; each Venusian sidereal day has
increased by 6.5 minutes in that time
span.[109] Because of the retrograde
rotation, the length of a solar day on Venus
is significantly shorter than the sidereal
day, at 116.75 Earth days (making the
Venusian solar day shorter than Mercury's
176 Earth days).[110] One Venusian year is
about 1.92 Venusian solar days.[111] To an
observer on the surface of Venus, the Sun
would rise in the west and set in the
east,[111] although Venus's opaque clouds
prevent observing the Sun from the
planet's surface.[112]
Venus may have formed from the solar
nebula with a different rotation period and
obliquity, reaching its current state
because of chaotic spin changes caused
by planetary perturbations and tidal
effects on its dense atmosphere, a change
that would have occurred over the course
of billions of years. The rotation period of
Venus may represent an equilibrium state
between tidal locking to the Sun's
gravitation, which tends to slow rotation,
and an atmospheric tide created by solar
heating of the thick Venusian
atmosphere.[113][114] The 584-day average
interval between successive close
approaches to Earth is almost exactly
equal to 5 Venusian solar days (5.001444
to be precise),[115] but the hypothesis of a
spin-orbit resonance with Earth has been
discounted.[116]

Venus has no natural satellites.[117] It has

several trojan asteroids: the quasi-satellite
2002 VE68[118][119] and two other
temporary trojans, 2001 CK32 and
2012 XE133.[120] In the 17th century,
Giovanni Cassini reported a moon orbiting
Venus, which was named Neith and
numerous sightings were reported over
the following 200 years, but most were
determined to be stars in the vicinity. Alex
Alemi's and David Stevenson's 2006 study
of models of the early Solar System at the
California Institute of Technology shows
Venus likely had at least one moon created
by a huge impact event billions of years
ago.[121] About 10 million years later,
according to the study, another impact
reversed the planet's spin direction and
caused the Venusian moon gradually to
spiral inward until it collided with
Venus.[122] If later impacts created moons,
these were removed in the same way. An
alternative explanation for the lack of
satellites is the effect of strong solar tides,
which can destabilize large satellites
orbiting the inner terrestrial planets.[117]
Observation

Venus is always brighter than all other planets or stars

as seen from Earth. The second brightest object on
the image is Jupiter.

To the naked eye, Venus appears as a

white point of light brighter than any other
planet or star (apart from the Sun).[123] The
planet's mean apparent magnitude is
−4.14 with a standard deviation of 0.31.[14]
The brightest magnitude occurs during
crescent phase about one month before or
after inferior conjunction. Venus fades to
about magnitude −3 when it is backlit by
the Sun.[124] The planet is bright enough to
be seen in a clear midday sky[125] and is
more easily visible when the Sun is low on
the horizon or setting. As an inferior
planet, it always lies within about 47° of
the Sun.[126]

Venus "overtakes" Earth every 584 days as

it orbits the Sun.[5] As it does so, it
changes from the "Evening Star", visible
after sunset, to the "Morning Star", visible
before sunrise. Although Mercury, the
other inferior planet, reaches a maximum
elongation of only 28° and is often difficult
to discern in twilight, Venus is hard to miss
when it is at its brightest. Its greater
maximum elongation means it is visible in
dark skies long after sunset. As the
brightest point-like object in the sky, Venus
is a commonly misreported "unidentified
flying object".

Phases

The phases of Venus and evolution of its apparent

diameter
As it orbits the Sun, Venus displays phases
like those of the Moon in a telescopic
view. The planet appears as a small and
"full" disc when it is on the opposite side
of the Sun (at superior conjunction). Venus
shows a larger disc and "quarter phase" at
its maximum elongations from the Sun,
and appears its brightest in the night sky.
The planet presents a much larger thin
"crescent" in telescopic views as it passes
along the near side between Earth and the
Sun. Venus displays its largest size and
"new phase" when it is between Earth and
the Sun (at inferior conjunction). Its
atmosphere is visible through telescopes
by the halo of sunlight refracted around
it.[126]

Transits

2004 transit of Venus

The Venusian orbit is slightly inclined

relative to Earth's orbit; thus, when the
planet passes between Earth and the Sun,
it usually does not cross the face of the
Sun. Transits of Venus occur when the
planet's inferior conjunction coincides with
its presence in the plane of Earth's orbit.
Transits of Venus occur in cycles of
243 years with the current pattern of
transits being pairs of transits separated
by eight years, at intervals of about
105.5 years or 121.5 years—a pattern first
discovered in 1639 by the English
astronomer Jeremiah Horrocks.[127]

The latest pair was June 8, 2004 and June

5–6, 2012. The transit could be watched
live from many online outlets or observed
locally with the right equipment and
conditions.[128]
The preceding pair of transits occurred in
December 1874 and December 1882; the
following pair will occur in December 2117
and December 2125.[129] The 1874 transit
is the subject of the oldest film known, the
1874 Passage de Venus. Historically,
transits of Venus were important, because
they allowed astronomers to determine
the size of the astronomical unit, and
hence the size of the Solar System as
shown by Horrocks in 1639.[130] Captain
Cook's exploration of the east coast of
Australia came after he had sailed to Tahiti
in 1768 to observe a transit of
Venus.[131][132]
Pentagram of Venus

The pentagram of Venus. Earth is positioned at the

centre of the diagram, and the curve represents the
direction and distance of Venus as a function of time.

The pentagram of Venus is the path that

Venus makes as observed from Earth.
Successive inferior conjunctions of Venus
repeat very near a 13:8 ratio (Earth orbits 8
times for every 13 orbits of Venus),
shifting 144° upon sequential inferior
conjunctions. The 13:8 ratio is
approximate. 8/13 is approximately
0.61538 while Venus orbits the Sun in
0.61519 years.[133]

Daylight apparitions

Naked eye observations of Venus during

daylight hours exist in several anecdotes
and records. Astronomer Edmund Halley
calculated its maximum naked eye
brightness in 1716, when many Londoners
were alarmed by its appearance in the
daytime. French emperor Napoleon
Bonaparte once witnessed a daytime
apparition of the planet while at a
reception in Luxembourg.[134] Another
historical daytime observation of the
planet took place during the inauguration
of the American president Abraham
Lincoln in Washington, D.C., on 4 March
1865.[135] Although naked eye visibility of
Venus's phases is disputed, records exist
of observations of its crescent.[136]

Ashen light

A long-standing mystery of Venus

observations is the so-called ashen light—
an apparent weak illumination of its dark
side, seen when the planet is in the
crescent phase. The first claimed
observation of ashen light was made in
1643, but the existence of the illumination
has never been reliably confirmed.
Observers have speculated it may result
from electrical activity in the Venusian
atmosphere, but it could be illusory,
resulting from the physiological effect of
observing a bright, crescent-shaped
object.[137][80]

Studies

Early studies
The "black drop effect" as recorded during the 1769
transit

Because the movements of Venus appear

to be discontinuous (it disappears due to
its proximity to the sun, for many days at a
time, and then reappears on the other
horizon), some cultures did not recognize
Venus as single entity;[138] instead, they
assumed it to be two separate stars on
each horizon: the morning and evening
star.[138] Nonetheless, a cylinder seal from
the Jemdet Nasr period and the Venus
tablet of Ammisaduqa from the First
Babylonian dynasty indicate that the
ancient Sumerians already knew that the
morning and evening stars were the same
celestial object.[139][138][140] In the Old
Babylonian period, the planet Venus was
known as Ninsi'anna, and later as
Dilbat.[141] The name "Ninsi'anna"
translates to "divine lady, illumination of
heaven", which refers to Venus as the
brightest visible "star". Earlier spellings of
the name were written with the cuneiform
sign si4 (= SU, meaning "to be red"), and
the original meaning may have been
"divine lady of the redness of heaven", in
reference to the colour of the morning and
evening sky.[142]

The Chinese historically referred to the

morning Venus as "the Great White" (Tài-
bái 太⽩) or "the Opener (Starter) of
Brightness" (Qǐ-míng 啟明), and the
evening Venus as "the Excellent West One"
(Cháng-gēng ⻑庚). [143]

The ancient Greeks also initially believed

Venus to be two separate stars:
Phosphorus, the morning star, and
Hesperus, the evening star. Pliny the Elder
credited the realization that they were a
single object to Pythagoras in the sixth
century BCE,[144] while Diogenes Laërtius
argued that Parmenides was probably
responsible for this rediscovery.[145]
Though they recognized Venus as a single
object, the ancient Romans continued to
designate the morning aspect of Venus as
Lucifer, literally "Light-Bringer", and the
evening aspect as Vesper, both of which
are literal translations of their traditional
Greek names.

In the second century, in his astronomical

treatise Almagest, Ptolemy theorized that
both Mercury and Venus are located
between the Sun and the Earth. The 11th-
century Persian astronomer Avicenna
claimed to have observed the transit of
Venus,[146] which later astronomers took
as confirmation of Ptolemy's theory.[147] In
the 12th century, the Andalusian
astronomer Ibn Bajjah observed "two
planets as black spots on the face of the
Sun"; these were thought to be the transits
of Venus and Mercury by 13th-century
Maragha astronomer Qotb al-Din Shirazi,
though this cannot be true as there were
no Venus transits in Ibn Bajjah's
lifetime.[148][n 2]
Galileo's discovery that Venus showed phases
(although remaining near the Sun in Earth's sky)
proved that it orbits the Sun and not Earth

When the Italian physicist Galileo Galilei

first observed the planet in the early
17th century, he found it showed phases
like the Moon, varying from crescent to
gibbous to full and vice versa. When Venus
is furthest from the Sun in the sky, it
shows a half-lit phase, and when it is
closest to the Sun in the sky, it shows as a
crescent or full phase. This could be
possible only if Venus orbited the Sun, and
this was among the first observations to
clearly contradict the Ptolemaic geocentric
model that the Solar System was
concentric and centred on Earth.[151][152]

The 1639 transit of Venus was accurately

predicted by Jeremiah Horrocks and
observed by him and his friend, William
Crabtree, at each of their respective
homes, on 4 December 1639 (24
November under the Julian calendar in use
at that time).[153]

The atmosphere of Venus was discovered

in 1761 by Russian polymath Mikhail
Lomonosov.[154][155] Venus's atmosphere
was observed in 1790 by German
astronomer Johann Schröter. Schröter
found when the planet was a thin crescent,
the cusps extended through more than
180°. He correctly surmised this was due
to scattering of sunlight in a dense
atmosphere. Later, American astronomer
Chester Smith Lyman observed a
complete ring around the dark side of the
planet when it was at inferior conjunction,
providing further evidence for an
atmosphere.[156] The atmosphere
complicated efforts to determine a
rotation period for the planet, and
observers such as Italian-born astronomer
Giovanni Cassini and Schröter incorrectly
estimated periods of about 24 h from the
motions of markings on the planet's
apparent surface.[157]

Ground-based research

Modern telescopic view of Venus from Earth's surface

Little more was discovered about Venus

until the 20th century. Its almost
featureless disc gave no hint what its
surface might be like, and it was only with
the development of spectroscopic, radar
and ultraviolet observations that more of
its secrets were revealed. The first
ultraviolet observations were carried out in
the 1920s, when Frank E. Ross found that
ultraviolet photographs revealed
considerable detail that was absent in
visible and infrared radiation. He
suggested this was due to a dense, yellow
lower atmosphere with high cirrus clouds
above it.[158]

Spectroscopic observations in the 1900s

gave the first clues about the Venusian
rotation. Vesto Slipher tried to measure
the Doppler shift of light from Venus, but
found he could not detect any rotation. He
surmised the planet must have a much
longer rotation period than had previously
been thought.[159] Later work in the 1950s
showed the rotation was retrograde. Radar
observations of Venus were first carried
out in the 1960s, and provided the first
measurements of the rotation period,
which were close to the modern value.[160]

Radar observations in the 1970s revealed

details of the Venusian surface for the first
time. Pulses of radio waves were beamed
at the planet using the 300 m (1,000 ft)
radio telescope at Arecibo Observatory,
and the echoes revealed two highly
reflective regions, designated the Alpha
and Beta regions. The observations also
revealed a bright region attributed to
mountains, which was called Maxwell
Montes.[161] These three features are now
the only ones on Venus that do not have
female names.[39]

Exploration

 
Artist's impression of Mariner 2, launched in 1962, a
skeletal, bottle-shaped spacecraft with a large radio
dish on top

The first robotic space probe mission to

Venus, and the first to any planet, began
with the Soviet Venera program in
1961.[162] The United States' exploration of
Venus had its first success with the
Mariner 2 mission on 14 December 1962,
becoming the world's first successful
interplanetary mission, passing 34,833 km
(21,644 mi) above the surface of Venus,
and gathering data on the planet's
atmosphere.[163][164]
 

180-degree panorama of Venus's surface from the

Soviet Venera 9 lander, 1975. Black-and-white image
of barren, black, slate-like rocks against a flat sky. The
ground and the probe are the focus. Several lines are
missing due to a simultaneous transmission of the
scientific data.

On 18 October 1967, the Soviet Venera 4

successfully entered the atmosphere and
deployed science experiments. Venera 4
showed the surface temperature was
hotter than Mariner 2 had calculated, at
almost 500 °C (932 °F), determined that
the atmosphere was 95% carbon dioxide
(CO2), and discovered that Venus's
atmosphere was considerably denser than
Venera 4's designers had anticipated.[165]
The joint Venera 4–Mariner 5 data were
analysed by a combined Soviet–American
science team in a series of colloquia over
the following year,[166] in an early example
of space cooperation.[167]

In 1974, Mariner 10 swung by Venus on its

way to Mercury and took ultraviolet
photographs of the clouds, revealing the
extraordinarily high wind speeds in the
Venusian atmosphere.
 

Global view of Venus in ultraviolet light done by

Mariner 10.

In 1975, the Soviet Venera 9 and 10 landers

transmitted the first images from the
surface of Venus, which were in black and
white. In 1982 the first colour images of
the surface were obtained with the Soviet
Venera 13 and 14 landers.

NASA obtained additional data in 1978

with the Pioneer Venus project that
consisted of two separate missions:[168]
Pioneer Venus Orbiter and Pioneer Venus
Multiprobe.[169] The successful Soviet
Venera program came to a close in
October 1983, when Venera 15 and 16
were placed in orbit to conduct detailed
mapping of 25% of Venus's terrain (from
the north pole to 30°N latitude)[170]

Several other Venus flybys took place in

the 1980s and 1990s that increased the
understanding of Venus, including Vega 1
(1985), Vega 2 (1985), Galileo (1990),
Magellan (1994), Cassini–Huygens (1998),
and MESSENGER (2006). Then, Venus
Express by the European Space Agency
(ESA) entered orbit around Venus in April
2006. Equipped with seven scientific
instruments, Venus Express provided
unprecedented long-term observation of
Venus's atmosphere. ESA concluded that
mission in December 2014.

As of 2016, Japan's Akatsuki is in a highly

elliptical orbit around Venus since 7
December 2015, and there are several
probing proposals under study by
Roscosmos, NASA, and India's ISRO.

In 2016, the NASA Innovative Advanced

Concepts program studied a rover, the
Automaton Rover for Extreme
Environments, designed to survive for an
extended time in Venus's environmental
conditions. It would be controlled by a
mechanical computer and driven by wind
power.[171]

In culture

Venus is portrayed just to the right of the large

cypress tree in Vincent van Gogh's 1889 painting The
Starry Night.[172][173]
Venus is a primary feature of the night sky,
and so has been of remarkable
importance in mythology, astrology and
fiction throughout history and in different
cultures.

In Sumerian religion, Inanna was

associated with the planet Venus.[174][175]
Several hymns praise Inanna in her role as
the goddess of the planet
Venus.[138][175][174] Theology professor
Jeffrey Cooley has argued that, in many
myths, Inanna's movements may
correspond with the movements of the
planet Venus in the sky.[138] The
discontinuous movements of Venus relate
to both mythology as well as Inanna's dual
nature.[138] In Inanna's Descent to the
Underworld, unlike any other deity, Inanna
is able to descend into the netherworld
and return to the heavens. The planet
Venus appears to make a similar descent,
setting in the West and then rising again in
the East.[138] An introductory hymn
describes Inanna leaving the heavens and
heading for Kur, what could be presumed
to be, the mountains, replicating the rising
and setting of Inanna to the West.[138] In
Inanna and Shukaletuda and Inanna's
Descent into the Underworld appear to
parallel the motion of the planet
Venus.[138] In Inanna and Shukaletuda,
Shukaletuda is described as scanning the
heavens in search of Inanna, possibly
searching the eastern and western
horizons.[176] In the same myth, while
searching for her attacker, Inanna herself
makes several movements that
correspond with the movements of Venus
in the sky.[138]

Classical poets such as Homer, Sappho,

Ovid and Virgil spoke of the star and its
light.[177] Poets such as William Blake,
Robert Frost,   Letitia Elizabeth Landon.,
Alfred Lord Tennyson and William
Wordsworth wrote odes to it.[178]
In Chinese the planet is called Jīn-xīng ( ⾦
星), the golden planet of the metal
element. In India Shukra Graha ("the planet
Shukra") which is named after a powerful
saint Shukra. Shukra which is used in
Indian Vedic astrology[179] means "clear,
pure" or "brightness, clearness" in Sanskrit.
One of the nine Navagraha, it is held to
affect wealth, pleasure and reproduction; it
was the son of Bhrgu, preceptor of the
Daityas, and guru of the Asuras.[180] The
word Shukra is also associated with
semen, or generation. Venus is known as
Kejora in Indonesian and Malay. Modern
Chinese, Japanese and Korean cultures
refer to the planet literally as the "metal
 ⾦星), based on the Five
star" (
elements.[181][182][183]

The Maya considered Venus to be the

most important celestial body after the
Sun and Moon. They called it Chac ek,[184]
or Noh Ek', "the Great Star".[185] The cycles
of Venus were important to their calendar.

The Ancient Egyptians and Greeks

believed Venus to be two separate bodies,
a morning star and an evening star. The
Egyptians knew the morning star as
Tioumoutiri and the evening star as
Ouaiti.[186] The Greeks used the names
Phōsphoros (Φωσϕόρος), meaning "light-
bringer" (whence the element phosphorus;
alternately Ēōsphoros (Ἠωςϕόρος),
meaning "dawn-bringer"), for the morning
star, and Hesperos (Ἕσπερος), meaning
"Western one", for the evening star.[187]
Though by the Roman era they were
recognized as one celestial object, known
as "the star of Venus", the traditional two
Greek names continued to be used, though
usually translated to Latin as
Lūcifer[187][188] and Vesper.

Modern fiction

With the invention of the telescope, the

idea that Venus was a physical world and
possible destination began to take form.

The impenetrable Venusian cloud cover

gave science fiction writers free rein to
speculate on conditions at its surface; all
the more so when early observations
showed that not only was it similar in size
to Earth, it possessed a substantial
atmosphere. Closer to the Sun than Earth,
the planet was frequently depicted as
warmer, but still habitable by humans.[189]
The genre reached its peak between the
1930s and 1950s, at a time when science
had revealed some aspects of Venus, but
not yet the harsh reality of its surface
conditions. Findings from the first
missions to Venus showed the reality to be
quite different, and brought this particular
genre to an end.[190] As scientific
knowledge of Venus advanced, science
fiction authors tried to keep pace,
particularly by conjecturing human
attempts to terraform Venus.[191]

Symbol

  The astronomical symbol for Venus is

the same as that used in biology for
the female sex: a circle with a small cross
beneath.[192] [193] The Venus symbol also
represents femininity, and in Western
alchemy stood for the metal
copper.[192] [193] Polished copper has been
used for mirrors from antiquity, and the
symbol for Venus has sometimes been
understood to stand for the mirror of the
goddess although that is not its true
origin.[192][193]

Habitability
The speculation of the existence of life on
Venus has decreased significantly since
the early 1960s, when spacecraft began
studying Venus and it became clear that
the conditions on Venus are extreme
compared to those on Earth.
That Venus is closer to the Sun than Earth,
raising temperatures on the surface to
nearly 735 K (462 °C; 863 °F), that its
atmospheric pressure is 90 times that of
Earth, and the extreme impact of the
greenhouse effect make water-based life
as currently known unlikely. A few
scientists have speculated that
thermoacidophilic extremophile
microorganisms might exist in the lower-
temperature, acidic upper layers of the
Venusian atmosphere.[194][195][196] The
atmospheric pressure and temperature
fifty kilometres above the surface are
similar to those at Earth's surface. This
has led to proposals to use aerostats
(lighter-than-air balloons) for initial
exploration and ultimately for permanent
"floating cities" in the Venusian
atmosphere.[197] Among the many
engineering challenges are the dangerous
amounts of sulfuric acid at these
heights.[197]

Nonetheless, in August 2019, astronomers

reported that newly discovered long-term
pattern of absorbance and albedo
changes in the atmosphere of the planet
Venus are caused by "unknown
absorbers", which may be chemicals or
even large colonies of microorganisms
high up in the atmosphere of the
planet.[198][77]

See also
Aspects of Venus
Geodynamics of Venus
Outline of Venus
Transit of Venus
Venus zone

Notes
1. Misstated as "Ganiki Chasma" in the
press release and scientific
publication.[48]
 2. Several claims of transit observations
made by medieval Islamic
astronomers have been shown to be
sunspots.[149] Avicenna did not record
the date of his observation. There was
a transit of Venus within his lifetime,
on 24 May 1032, although it is
questionable whether it would have
been visible from his location.[150]

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External links
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Venus profile at NASA's Solar System

Exploration site
Missions to Venus and Image catalog
at the National Space Science Data
Center
Soviet Exploration of Venus and Image
catalog at Mentallandscape.com
Image catalog from the Venera
missions
Venus page at The Nine Planets
Transits of Venus at NASA.gov
 Geody Venus , a search engine for
surface features
Interactive 3D gravity simulation of the
pentagram that the orbit of Venus traces
when Earth is held fixed at the centre of
the coordinate system

Cartographic resources

Map-a-Planet: Venus by the U.S.

Geological Survey
Gazetteer of Planetary Nomenclature:
Venus by the International
Astronomical Union
Venus crater database by the Lunar and
Planetary Institute
 Map of Venus by Eötvös Loránd
University
Google Venus 3D , interactive map of
the planet

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