Planet Venus. In Roman mythology, “Venus” was the goddess of love and fertility

Planet Venus

In Roman mythology, “Venus” was the goddess of love and fertility.

Venus was the equivalent of the Greek goddess, “Aphrodite”.

Venus was the consort of Vulcan…

…and Vulcan was the

god of fire.

The word “volcano” comes from the word “Vulcan”.

Here we see Venus locked in an embrace with Vulcan.

The Roman people are believed to descend from them.

For centuries, she has been called the “goddess of love”.

And in addition to that, she also goes by 2 other nicknames.

Venus is sometimes referred to as the morning or evening star.

Under favorable conditions, Venus is so bright…

…that it can even cast a shadow on Earth.

After the Moon, Venus is the brightest object in the sky.

Notice how bright Venus is, when compared with a nearby star.

Venus also has a third nickname.

It is often referred toas “Earth’s sister planet”.

At 95% the diameter of Earth, the 2 planets are nearly

the same size.

100% 95%

Venus also has 82% the mass of the Earth.

100% 95%

A History of VenusComplicated history; still poorly understood.

Very similar to Earth in mass, size, composition, density, but no magnetic field Core solid?

Solar wind interacts Solar wind interacts directly with the directly with the atmosphere, forming a bow atmosphere, forming a bow shock and a long ion tail. shock and a long ion tail.

COCO22 produced during produced during

outgassing remained in outgassing remained in atmosphere (on Earth: atmosphere (on Earth: dissolved in water).dissolved in water).

Heat transport from core mainly through magma flows close to the surface ( coronae, pancake domes, etc.)

Any water present on the Any water present on the surface rapidly evaporated surface rapidly evaporated → → feedback through enhancement feedback through enhancement of greenhouse effectof greenhouse effect

Venus is only the second planet in order of planets away from the

Most of the time, Venus is our closest neighbor in

space.

The average distance from the Earth to the Sun is 1 AU.

0.72 AU

However, Venus’ average distance is only 0.72 AUs from the Sun.

_______1.00 AU

0.72 AU= 1.39 x closer

0.72 AU

This makes Venus 1.39x closer to the Sun than the

Earth.

(1.39)2 = 1.93 x bigger

0.72 AU

In being 1.39x closer to the Sun, the Sun appears to be 1.93x

bigger.

This is how big the Sun appears when viewed from Earth.

The Sun as seen from Earth

The Sun as seen from Venus

1.93 x bigger

And here’s how big the Sun appears when viewed from Venus.

When Venus and the Earth are both on the same side of the Sun…

…then Venus is the Earth’s closest neighbor in space.

At this location, Venus is only 0.28 AUs from Earth.

1.00 AUs – 0.72 AUs = 0.28 AUs

0.28 AUs

However, when Venus is on the opposite side of the Earth…

…then Venus is no longer the closest planet to the Earth.

At this location, Venus lies 1.72 AUs from the Earth.

1.00 AUs0.72 AUs

1.00 AUs + 0.72 AUs = 1.72 AUs

At this location, Venus lies 1.72 AUs from the Earth.

When at its greatest elongation…

greatest elongation (aphelion)

Venus is never found more than 47o

away from the Sun.

greatest elongation (aphelion)

least elongation (perihelion)

And when at its least elongation…

Venus is never found more than 39o

away from the Sun.

least elongation (perihelion)

No matter where Venus is found in its orbit…

midnight

…Venus is never visible when viewed from the Earth at midnight.

Venus is also never visible when viewed from the Earth at noon.

No planets are visible in the daytime sky…

…because the Sun’s light drowns them all out.

So at what time of the day would Venus be visible from the

Earth?

Only in the mornings or in the evenings.

And only when Venus is in one of these

positions.

This is why Venus is sometimes referred to…

…as the morning or evening star.

This photo tracks Venus over a 7 month period of time.

Notice its position in the sky when at its greatest

elongation.

Notice its position in the sky when at its greatest

elongation.

greatest elongation

setting Sun

greatest elongation

At this location, Venus is 47o away from the setting Sun.

Space Probes to Venus

Venus has been visited by a number of space probes.

On its way to Mercury in 1974, Venus was visited by “Mariner 10”.

The next probe to visit Venus was “Pioneer Venus” in 1978.

But the mission of Pioneer Venus took the exploration of Venus a step further.

While Pioneer Venus itself remained in orbit around Venus...

…the 5 smaller probes it carried were dropped to the Venusian

surface.

Each of the 5 probes landed in a different location on Venus.

However, only one of the probes was operational…

…by the time they had all reached the ground.

The surviving probe transmitted information for about an hour.

Eventually it became inoperative due to the tremendous heat and

pressure.

The Magellan space probe was sent to Venus in 1993.

Of all the probes sent to Venus…

…it has by far yielded the best results.

Magellan’s main mission was to map the surface using radar.

Information was taken in strips then the data was radioed back to

the Earth.

Most of the Venus photos you will see came from the Magellan mission.

While the United States concentrated only on orbiting Venus…

The Soviet Union, on the other hand, concentrated on landing on

the surface.

Their Venera 13 spacecraft took the only photograph of its

surface.

Here is the same photo artificially

adjusted for color.

The dried rock and soil resemble dried streambeds on Earth.

Here is a close-up of the same photo.

Part of the spacecraft’s footpad are seen in the photograph.

Phases of Venus

The orbit of Venus lies entirely inside the orbit of the Earth.

When viewed from Earth, Venus passes through a full cycle of phases.

Since it is only visible in the daytime sky…

…then the “Full Venus” can never be seen from Earth.

Full Venus

…then the “Full Venus” can never be seen from Earth.

It was this discovery… as well as the phases of Venus…

…which convinced Galileo that the heliocentric model was correct.

Rotation VS

Revolution

The Rotation of Venus

• Almost all planets rotate counterclockwise, i.e. in the same sense as orbital motion.

• Exceptions: Venus, Uranus and Pluto

• Venus rotates clockwise, with period slightly longer than orbital period.

Possible reasons:

• Off-center collision with massive protoplanet

• Tidal forces of the sun on molten core

RevolutionDays

000.00

Venus orbits the Sun with a 225-day period of revolution.

RevolutionDays

014.06

RevolutionDays

028.13

RevolutionDays

042.19

RevolutionDays

056.25

RevolutionDays

070.31

RevolutionDays

084.38

RevolutionDays

098.44

RevolutionDays

112.50

RevolutionDays

126.56

RevolutionDays

140.63

RevolutionDays

154.69

RevolutionDays

168.75

RevolutionDays

182.81

RevolutionDays

196.88

RevolutionDays

210.94

RevolutionDays

225.00

Venus revolves around the Sun in a counter-clockwise direction.

counter-clockwise

However, Venus is the only planet to rotate in a clockwise direction.

clockwise

This means that noon-to-noon on Venus…

Synodic Rotation

000.00

…will occur in only 116 days.

Synodic Rotation

014.50

Synodic Rotation

029.00

Synodic Rotation

043.50

Synodic Rotation

058.00

Synodic Rotation

058.00

midnight

Synodic Rotation

058.00

Synodic Rotation

072.50

Synodic Rotation

087.00

Synodic Rotation

101.50

Synodic Rotation

116.00

Synodic Rotation

116.00

Even though it only takes 116 days for Venus to experience its second

noon…

…it has not yet completed, even half a rotation on its axis.

Synodic Rotation

000.00

Watch its synodic rotation again.

Synodic Rotation

000.00

Synodic Rotation

014.50

Synodic Rotation

029.00

Synodic Rotation

043.50

Synodic Rotation

058.00

Synodic Rotation

058.00

midnight

Synodic Rotation

058.00

Synodic Rotation

072.50

Synodic Rotation

087.00

Synodic Rotation

101.50

Synodic Rotation

116.00

Synodic Rotation

116.00noon

000.00

pointing upward

Sidereal Rotation

A sidereal rotation, on the other hand, requires 243 days to

complete.

000.00

Sidereal Rotation

complete.

014.50

Sidereal Rotation

complete.

029.00

Sidereal Rotation

complete.

043.50

Sidereal Rotation

complete.

058.00

Sidereal Rotation

complete.

072.50

Sidereal Rotation

complete.

087.00

Sidereal Rotation

complete.

101.50

Sidereal Rotation

complete.

116.00

Sidereal Rotation

complete.

130.50

Sidereal Rotation

complete.

145.00

Sidereal Rotation

complete.

159.50

Sidereal Rotation

complete.

174.00

Sidereal Rotation

complete.

188.50

Sidereal Rotation

complete.

203.00

Sidereal Rotation

complete.

217.50

Sidereal Rotation

complete.

232.00

Sidereal Rotation

complete.

243.00

Sidereal Rotation

complete.

243.00

Sidereal Rotation

pointing upward

complete.

This means that the day on Venus is longer than Venus’ year.

pointing upward

Let’s watch the sidereal rotation again and keep a tally of what we observe.

000.00Day Counter

Sidereal

Revolution

Synodic

pointing upward

000.00Day Counter

Sidereal

Revolution

Synodic

014.50Day Counter

Sidereal

Revolution

Synodic

029.00Day Counter

Sidereal

Revolution

Synodic

043.50Day Counter

Sidereal

Revolution

Synodic

058.00Day Counter

Sidereal

Revolution

Synodic

072.50Day Counter

Sidereal

Revolution

Synodic

087.00Day Counter

Sidereal

Revolution

Synodic

101.50Day Counter

Sidereal

Revolution

Synodic

116.00Day Counter

Sidereal

Revolution

Synodic

116.00Day Counter

Sidereal

Revolution

Synodic

At 116 days,

116.00Day Counter

Sidereal

Revolution

Synodic

At 116 days, Venus completes one noon-to-noon.

116.00Day Counter

Sidereal

Revolution

Synodic

116.00Day Counter

Sidereal

Revolution

Synodic

116.00Day Counter

Sidereal

Revolution

Synodic

116.00Day Counter

Sidereal

Revolution

Synodic

130.50Day Counter

Sidereal

Revolution

Synodic

145.00Day Counter

Sidereal

Revolution

Synodic

159.50Day Counter

Sidereal

Revolution

Synodic

174.00Day Counter

Sidereal

Revolution

Synodic

188.50Day Counter

Sidereal

Revolution

Synodic

203.00Day Counter

Sidereal

Revolution

Synodic

217.50Day Counter

Sidereal

Revolution

Synodic

225.00Day Counter

Sidereal

Revolution

Synodic

225.00Day Counter

Sidereal

Revolution

Synodic

At 225 days,

225.00Day Counter

Sidereal

Revolution

Synodic

At 225 days, Venus competes one revolution.

225.00Day Counter

Sidereal

Revolution

Synodic

225.00Day Counter

Sidereal

Revolution

Synodic

225.00Day Counter

Sidereal

Revolution

Synodic

232.00Day Counter

Sidereal

Revolution

Synodic

232.00Day Counter

Sidereal

Revolution

Synodic

At 232 days,

232.00Day Counter

Sidereal

Revolution

Synodic

At 232 days, Venus competes its second noon-to-noon.

232.00Day Counter

Sidereal

Revolution

Synodic

232.00Day Counter

Sidereal

Revolution

Synodic

232.00Day Counter

Sidereal

Revolution

Synodic

232.00Day Counter

Sidereal

Revolution

Synodic

243.00Day Counter

Sidereal

Revolution

Synodic

243.00Day Counter

Sidereal

Revolution

Synodic

And finally, at 243 days, Venus competes its first sidereal

243.00Day Counter

Sidereal

Revolution

Synodic

243.00Day Counter

Sidereal

Revolution

Synodic

243.00Day Counter

Sidereal

Revolution

Synodic

The rotational period of Venus was difficult to establish for 2 reasons.

In the first place, Venus has a slow rotation rate.

The second reason has to do with its clouds.

The surface of Venus is enshrouded within a thick cloud

clover.

thick cloud cover

In visible light wavelengths, it’s surface is impossible to view.

thick cloud cover

But with the help of cloud-penetrating radar…

…the Venusian surface is revealed in fine detail.

This photo is a radio image taken by the Magellan space probe in 1993.

When false color is added to the image…

…then plateaus and lowlands are brought into view.

North Pole

equator

rotation: clockwise

radio telescope(satellite dish)

Just like with Mercury…

…the Doppler Effect and radar revealed the rotation rate on Venus.

red-shifted

receding side

red-shifted

blue-shifted

approaching side

red-shifted

blue-shifted

The fact that there was a red and blue shift…

red-shifted

blue-shifted

…is what determined that Venus was rotating in the first place.

red-shifted

blue-shifted

It was the amount of red and blue shift…

red-shifted

blue-shifted

…which determined the rate at which Venus rotated on its axis.

Planet Venus

Tilt on the Axis

The Earth is tilted by 23.5o on its axis.

Venus, however, is only tilted by 3o on its axis.

Because it is nearly vertical, Venus does not experience

seasons.

The Surface of Venus

Once radar from Magellan had penetrated the thick clouds

on Venus…

…its surface was revealed in fine detail.

Magellan mapped the surface of Venus in long strips called “noodles”.

The black lines seen in this photo represent places where

data is missing.

Approximately 90% of the Venusian surface is relatively flat terrain (lowlands).

The remaining 10% of the surface is elevated plateaus

(highlands).

The 2 largest highlands are Aphrodite Terra and Ishtar Terra.

Aphrodite Terra is the larger of the two.

It stretches halfway around the equator.

Ishtar Terra is found in the North.

It contains the Maxwell Mountain Range.

Lakshmi Planum and Maxwell Mountains

Radar image

Wrinkled mountain formations indicate compression and wrinkling, though there is no evidence of plate tectonics on Venus.

The surface of Venus contains thousands of active volcanoes.

Shield Volcanoes

Found above hot spots:

Fluid magma chamber, from which lava erupts repeatedly through surface layers above.

All volcanoes on Venus and Mars are shield volcanoes

Shield Volcanoes (2)

Tectonic plates moving over hot spots producing shield volcanoes Chains of volcanoes

Example: The Hawaiian Islands

At 8 km in elevation Maat Mons is the highest in elevation.

Gula Mons is about 3 km in elevation.

The 3-D perspective shown here was vertically exaggerated by computers.

Shown in this photo are the “pancake

dome” volcanoes.

They are characterized by flat tops and steep sides.

The lava forming their sides was highly viscous and slow-flowing.

The lava hardened before it had a chance to spread out.

Evidence of lava flows can be seen everywhere on Venus.

The lava from this volcano flowed for hundreds of kilometers.

Also notice the large impact crater shown in the center of the

photo.

Volcanism on Venus

Sapas Mons (radar image)

2 lava-filled calderas~ 400 km (250 miles)

Lava flows

Volcanic Features on Venus

Baltis Vallis: 6800 km long lava flow channel (longest

in the solar system!) Coronae: Circular bulges formed by volcanic activity

Aine Corona

Pancake Domes:

Associated with volcanic

activity forming coronae

Some lava flows collapsed after molten lava drained away

Venus only has 10-20% as many impact craters as the lunar maria.

This suggests a surface age of less than 1 billion years old.

Many of the smaller meteorites burn up in the thick atmosphere.

The circles shown on this map plot the locations of impact craters.

Since the craters are evenly distributed…

…then the surface of Venus must all be the same age.

While there is no evidence of plate tectonics on Venus…

…this photo shows a feature known as “Rift Valley”.

The Interior of Venus

There is much debate and disagreement about the internal structure of Venus.

rocky crust

metallic core

viscous mantle

But just like the other planets, Venus certainly has the same 3 layers.

Venus appears to lack the necessary ingredients to generate a magnetic

(no liquid core?)

Venus has a very weak magnetic field.

(About 25,000 times weaker than Earth’s)

rocky crust

metallic core

viscous mantle

With no detectable magnetic field the core is believed to be solid.

Surface Temperature

The surface temperature on Venus is a smoldering 800o F.

This means that Venus is 800o Fall day, all night, all year long.

One place on Venus is as hot as any other place on Venus.

If oceans had ever existed in the distant past…

…they have long since boiled away in all of this unimaginable heat.

With virtually no tilt on its axis…

…all 4 seasons share the exact same climate.

Like ceramic pottery baking in a hot kiln oven…

…the surface rocks on Venus slowly cook in the searing heat.

At only 90o F, however, the clouds of Venus are quite a bit

cooler.

Sulfur and water vapor combine to form clouds of sulfuric acid.

Sulfuric acid is also the type of acid found in car batteries.

The clouds are continually re-supplied with sulfur from active volcanoes.

But even though sulfuric acid rains down from the clouds on

Venus...

…those raindrops evaporate before ever reaching the ground.

Even more inhospitable are the electrical storms on Venus.

Both day and night alike, electricity rains down from its skies.

Imagine the dangers of trying to land a spacecraft on Venus.

If the heat and electricity didn’t kill the crew…

…then they would be crushed to death by the thick atmospheric pressure.

The atmospheric pressure on Venus is 100X thicker than the Earth’s.

15 lbs. / in2

Since the atmospheric pressure on Earth is about 15 lbs/in2 at sea level…

1500 lbs. / in2

…then the atmospheric pressure on Venus is about 1500 lbs/in2.

15 lbs. / in2

Composition of Venus’ Atmosphere

The atmosphere of Venus is composed largely of just 2 gases.

carbon dioxidenitrogen 3.5 %

96.5 %==

____________________________

With an atmosphere consisting mostly carbon dioxide…

carbon dioxidenitrogen 3.5 %

96.5 %==

____________________________

…Venus experiences a runaway

greenhouse effect.

carbon dioxide

nitrogen 3.5 %

96.5 %=

____________________________

The Runaway Greenhouse Effect

The main reason why Venus is so bright…

70% reflected back into space

…is because its white clouds reflect 70% of the sunlight striking

Venus’ albedo = 0.7

albedo – the reflectivity of a surface.

This makes for a very bright planet.

Below the clouds, the air is clear.

The remaining sunlight trickles through the thick cloud cover.

Sunlight cannot shine directly onto the Venusian surface…

diffuse visible light

…because the clouds serve as a filter, making the light “diffuse”.

This kind of light does not cast shadows.

Upon reaching the ground the visible light is absorbed by the surface.

The waves are then re-emitted at the longer wavelength of infrared.

infrared

trapped by CO2,

Like a greenhouse, the heat is trapped and cannot escape.

H2O vapor, and clouds

infrared

trapped by CO2,

Venus is not receiving, however, more energy than it emits back

into space.

infrared

trapped by CO2,

Some energy

must escape back into space.

infrared

escaping energy

trapped by CO2,

The amount of energy coming in from the Sun…

infrared

escaping energy

trapped by CO2, H2O vapor, and clouds

energy in = energy out

…must equal the amount of energy that escapes back into

space.

infrared

escaping energy

If this were not the case, then Venus would explode.

infrared

escaping energy

Every single day, its temperature would have climbed higher.

infrared

escaping energy

After 4 billions of years of this, its temperature would be in the trillionso F.

infrared

escaping energy

VenusVenus Statistics

Mass (kg) 4.869e+24 Mass (Earth = 1) .81476 Equatorial radius (km) 6,051.8 Equatorial radius (Earth = 1) .94886 Mean density (gm/cm^3) 5.25 Mean distance from the Sun (km) 108,200,000 Mean distance from the Sun (Earth = 1) 0.7233 Rotational period (days) -243.0187 Orbital period (days) 224.701 Mean orbital velocity (km/sec) 35.02 Orbital eccentricity 0.0068 Tilt of axis (degrees) 177.36 Orbital inclination (degrees) 3.394 Equatorial surface gravity (m/sec^2) 8.87 Equatorial escape velocity (km/sec) 10.36 Visual geometric albedo 0.65 Magnitude (Vo) -4.4 Mean surface temperature 482°C Atmospheric pressure (bars) 92 Atmospheric composition Carbon dioxide 96% Nitrogen 3+% Trace amounts of: Sulfur dioxide, water vapor,carbon monoxide, argon, helium, neon,hydrogen chloride, and hydrogen fluoride.

Planet Venus. In Roman mythology, “Venus” was the goddess of love and fertility

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