the terrestrial planets. earth mars venus mercury because the 4 inner planets have solid, rocky...

The Terrestrial

Planets

Earth

Mars

Venus

Mercury

Because the 4 inner planets have solid, rocky terrains…

Earth

Mars

Venus

Mercury

…they are sometimes called the “terrestrial planets”.

Earth

Mars

Venus

Mercury

Starting with Mercury, each planet will be discussed in detail.

Mercury

The “planet” Mercury was named for

the “Roman god” Mercury.

In Roman mythology, Mercury was the

god of trade and commerce.

The word, “merchant” contains the same root as the word, “Mercury”.

Mercury was also

the son of Jupiter.

Mercury is only slightly larger than the Earth’s Moon.

Earth

MercuryMoon

In order of planets away from the Sun, Mercury is the innermost planet.

Because it is so close to the Sun, it is often quite difficult to observe.

Here we see the Moon just after sunset.

Did you also notice Mercury in the sky?

Although Mercury is one of the brightest objects in the

sky…

…most people, have never seen it.

On his deathbed, for example, Galileo lamented the fact…

…that he was dying without ever having seen Mercury.

At its greatest elongation…

greatest elongation (aphelion)

28o

greatest elongation (aphelion)

…Mercury is never found more than 28o away from the Sun.

At its least elongation…

least elongation (perihelion)

…Mercury is only found at 18o away from the Sun.

least elongation (perihelion)

18o

This means that Mercury is never far from

the setting Sun.

This photo shows the highest position that Mercury reaches on various dates.

On February 8, Mercury is at its greatest elongation.

setting Sun

On this date, it should be 28o away from the setting Sun.

28o

Just like Venus and the Moon…

…Mercury also experiences a full cycle of phases.

Because only 2 of those phases are visible from Earth…

Mercury is only visible for about 1 week at a time, twice per year.

Recall that distances within the solar system…

…are measured in “astronomical units”.

And that 1astronomical unit…

…is the average distance from the Earth to the Sun.

1 AU

Mercury’s distance, on the other hand…

is found at only 0.39 AUs from the Sun.

0.39 AU

_______

This makes Mercury 2.5x closer to the Sun than

the Earth.

0.39 AU

1.00 AU

0.39 AU= 2.5 x closer

0.39 AU

(2.5)2 = 6.25 x bigger

In being 2.5x closer to the Sun, the Sun appears to be 6.25x

bigger.

If this is how big the Sun appears when viewed from Earth…

The Sun as seen from Earth

…then here’s how big the Sun appears when viewed from Mercury.

The Sun as seen from Earth

The Sun as seen from Mercury

6.25 x bigger

Rotation and

Revolution

rotation: counter-clockwise

North Pole

Mercury

equator

radio telescope(satellite dish)

Mercury’s rotation was

difficult to determine.

For one thing, it rotates very slowly.

Secondly, in being so close to the Sun, its surface is difficult to observe.

However, using the Doppler Effect, Mercury’s rotation was calculated.

same wavelengths

Identical radio waves leave the dish with the same wavelengths.

approaching side

From the approaching side, the returning waves are shorter.

shorter

blue-shifted

Since they are shorter, this means that they are blue shifted.

blue-shifted

receding side

From the receding side, however, the returning waves are longer.

longer

blue-shifted

red-shifted

And since they are longer, this means that they are red shifted.

blue-shifted

red-shifted

It’s the amount of red and blue shift…

blue-shifted

red-shifted

…which determines Mercury’s rate of rotation.

blue-shifted

red-shifted

The faster Mercury rotates on its axis…

blue-shifted

red-shifted

…the more red and blue shift will be observed.

blue-shifted

red-shifted

The slower Mercury rotates on its axis…

blue-shifted

red-shifted

…the less red and blue shiftwill be observed.

Mercury revolves the Sun in only 88 days.

Revolution

00.00Days


Revolution

05.50Days


Revolution

11.00Days


Revolution

16.50Days


Revolution

22.00Days


Revolution

29.50Days


Revolution

33.00Days


Revolution

38.50Days


Revolution

44.00Days


Revolution

49.50Days


Revolution

55.00Days


Revolution

60.50Days


Revolution

66.00Days


Revolution

71.50Days


Revolution

77.00Days


Revolution

82.50Days


DaysRevolution

88.00Days

Mercury rotates on its axis with a sidereal period of 59 days.

Sidereal Rotation

00.00Days


Sidereal Rotation

07.38Days


Sidereal Rotation

14.75Days


Sidereal Rotation

22.12Days


Sidereal Rotation

29.50Days


Sidereal Rotation

36.88Days


Sidereal Rotation

44.25Days


Sidereal Rotation

51.63Days


Sidereal Rotation

59.00Days


Sidereal Rotation

59.00Days pointing

upward

Mercury’s noon-to-noon, however, requires 176 days to complete.

Synodic Rotation

000.00Days


Synodic Rotation

007.36Days


Synodic Rotation

014.75Days


Synodic Rotation

022.12Days


Synodic Rotation

029.50Days


Synodic Rotation

036.88Days


Synodic Rotation

044.25Days


Synodic Rotation

051.63Days


Synodic Rotation

059.00Days


Synodic Rotation

066.37Days

Synodic Rotation

073.74Days


Synodic Rotation

081.11Days


Synodic Rotation

088.00Days


Synodic Rotation

095.36Days


Synodic Rotation

102.24Days


Synodic Rotation

111.12Days


Synodic Rotation

118.00Days


Synodic Rotation

123.63Days


Synodic Rotation

131.25Days


Synodic Rotation

138.90Days


Synodic Rotation

146.50Days


Synodic Rotation

154.12Days


Synodic Rotation

161.75Days


Synodic Rotation

169.38Days


Synodic Rotation

176.00Days


Synodic Rotation

176.00Days


noon

Notice the relationship between Mercury’s noon-to-noon and its year.

176 days = (88 days) x 2

Its noon-to-noonis exactly twice as long as its year.

Notice also that the 176-day synodic rotation…

176 days = (59 days) x 3

…is exactly equal to 3 sidereal rotations.

It’s merely a coincidence how these numbers relate to each other.

000.00Day Counter

0

00

Sidereal

Revolution

Synodic

007.38Day Counter

0

00

Sidereal

Revolution

Synodic

014.78Day Counter

0

00

Sidereal

Revolution

Synodic

022.15Day Counter

0

00

Sidereal

Revolution

Synodic

029.52Day Counter

0

00

Sidereal

Revolution

Synodic

036.89Day Counter

0

00

Sidereal

Revolution

Synodic

044.26Day Counter

0

00

Sidereal

Revolution

Synodic

051.63Day Counter

0

00

Sidereal

Revolution

Synodic

059.00Day Counter

0

00

Sidereal

Revolution

Synodic

059.00Day Counter

0

10

Sidereal

Revolution

Synodic

059.00Day Counter

0

10

Sidereal

Revolution

Synodic

After 59 days in orbit,

059.00Day Counter

0

10

Sidereal

Revolution

Synodic

After 59 days in orbit, Mercury completes 1 sidereal day.

059.00Day Counter

0

10

Sidereal

Revolution

Synodic

066.37Day Counter

0

10

Sidereal

Revolution

Synodic

073.74Day Counter

0

10

Sidereal

Revolution

Synodic

081.11Day Counter

0

10

Sidereal

Revolution

Synodic

088.00Day Counter

0

10

Sidereal

Revolution

Synodic

088.00Day Counter

0

10

Sidereal

Revolution

Synodic

After 88 days in orbit, Mercury completes 1 revolution.

088.00Day Counter

0

11

Sidereal

Revolution

Synodic

After 88 days in orbit, Mercury completes 1 revolution.

088.00Day Counter

0

11

Sidereal

Revolution

Synodic

096.36Day Counter

0

11

Sidereal

Revolution

Synodic

103.24Day Counter

0

11

Sidereal

Revolution

Synodic

111.12Day Counter

0

11

Sidereal

Revolution

Synodic

118.00Day Counter

0

11

Sidereal

Revolution

Synodic

118.00Day Counter

0

11

Sidereal

Revolution

Synodic

After 118 days in orbit, Mercury completes 2 sidereal days.

118.00Day Counter

0

21

Sidereal

Revolution

Synodic

After 118 days in orbit, Mercury completes 2 sidereal days.

118.00Day Counter

0

21

Sidereal

Revolution

Synodic

123.63Day Counter

0

21

Sidereal

Revolution

Synodic

131.25Day Counter

0

21

Sidereal

Revolution

Synodic

138.90Day Counter

0

21

Sidereal

Revolution

Synodic

145.50Day Counter

0

21

Sidereal

Revolution

Synodic

154.12Day Counter

0

21

Sidereal

Revolution

Synodic

161.75Day Counter

0

21

Sidereal

Revolution

Synodic

169.38Day Counter

0

21

Sidereal

Revolution

Synodic

176.00Day Counter

0

21

Sidereal

Revolution

Synodic

176.00Day Counter

0

21

Sidereal

Revolution

Synodic

After 176 days in orbit, 3 things happen with Mercury.

176.00Day Counter

0

21

Sidereal

Revolution

Synodic

176.00Day Counter

0

21

Sidereal

Revolution

Synodic

Mercury achieves

176.00Day Counter

0

21

Sidereal

Revolution

Synodic

Mercury achieves its third sidereal day.

176.00Day Counter

0

31

Sidereal

Revolution

Synodic

Mercury achieves its third sidereal day.

176.00Day Counter

0

31

Sidereal

Revolution

Synodic

176.00Day Counter

0

31

Sidereal

Revolution

Synodic

It also completes

176.00Day Counter

0

31

Sidereal

Revolution

Synodic

It also completes 2 revolutions around the Sun.

176.00Day Counter

0

32

Sidereal

Revolution

Synodic

It also completes 2 revolutions around the Sun.

176.00Day Counter

0

32

Sidereal

Revolution

Synodic

176.00Day Counter

0

32

Sidereal

Revolution

Synodic

And at the same time,

176.00Day Counter

0

32

Sidereal

Revolution

Synodic

And at the same time, Mercury also completes 1 synodic

day.

176.00Day Counter

1

32

Sidereal

Revolution

Synodic

And at the same time, Mercury also completes 1 synodic

day.

176.00Day Counter

1

32

Sidereal

Revolution

Synodic

176.00Day Counter

1

32

Sidereal

Revolution

Synodic

Since the number “176”

176.00Day Counter

1

32

Sidereal

Revolution

Synodic

Since the number “176” is a multiple of both “88” and “59”…

176.00Day Counter

1

32

Sidereal

Revolution

Synodic

176.00Day Counter

1

32

Sidereal

Revolution

Synodic

…then all 3 of these numbers

176.00Day Counter

1

32

Sidereal

Revolution

Synodic

…then all 3 of these numbers changed on exactly the same day.

Space Probes to Mercury

Mercury was visited by the Mariner 10 spacecraft in 1974.

Mariner 10 mapped Mercury’s surface, and took the first close-up photographs.

In 2004 NASA launched the Mercury

Messenger probe.

This was only the second probe ever sent to the planet Mercury.

In January, 2008 Messenger arrived at Mercury.

Messenger’s discoveries are yet to be revealed.

Mercury’s Interior

Mercury’s density is much higher than the Moon’s density.

This indicates that Mercury’s core has a high concentration of heavy

metals.

60% of Mercury’s total mass consists of an iron-nickel core.

iron-nickel core

iron-nickel corerocky crust

The surrounding crust consists of silicate rock.

iron-nickel corerocky crust

700 km

Mercury’s rocky crust is nearly 700 km thick.

This slide compares the cores of the Earth, Moon, and Mercury.

Notice that Mercury’s core is a ball of metal the size of the Moon.

A weak magnetic field has been detected around Mercury.

This indicates that some portion of the core is liquid.

History of Mercury

Dominated by ancient lava

flows and heavy meteorite

bombardment.

Radar image suggests icy

polar cap.

Mercury shows no evidence of plate tectonics or faulting.

However, its surface has long creases.

These creases formed from wrinkling caused when

Mercury cooled and shrank.

The Surface of Mercury

Very similar to Earth’s moon:

Heavily battered with craters, including some large basins.

Largest basin: Caloris Basin

Terrain on the opposite side jumbled by seismic waves

from the impact.

Lobate Scarps

Curved cliffs, probably formed when Mercury shrank while cooling down

The Plains of MercuryNo large maria, but intercrater plains:

Marked by smaller craters (< 15 km) and secondary impacts

Smooth plains:

Even younger than intercrater plains

Mercury VS

The Moon

The surface of Mercuryresembles the surface of the Moon.

Can you look at the 2 photos and tell which one is Mercury?

MoonMercury

Can you look at the 2 photos and tell which one is Mercury?

Both bodies are heavily cratered.

Moon Mercury

Both bodies are similar

in size and appearance.

Moon Mercury

And neither body has an atmosphere.

Moon Mercury

There are 2 reasons why Mercury has no atmosphere.

In the first place, the surface gravity on Mercury is too low.

With so little gravity, it is unable to retain an atmosphere.

Secondly, in being so close to the Sun…

…heated gases have the kinetic energy to escape Mercury and to fly off

into space.

Look closely at the 2 crescents.

Which side is Mercury, and which side is the Moon?

If this was your guess, then you were correct.

Mercury Moon

Here’s another one: Mercury or the Moon?

It’s Mercury, but it also looks like the lunar surface.

It’s Mercury, but it also looks like the lunar surface.

Mercury Moon

Surface Temperature

Mercury’s temperature range is the greatest of any planet.

Its daytime temperature can reach 700o Fahrenheit.

700o F

700o F -100o F

And its nighttime temperature can reach -100o Fahrenheit.

All planets without atmospheres get very cold at night.

700o F -100o F

But because Mercury is so close to the Sun…

700o F -100o F

…its daytime temperatures exceed those of all other planets.

700o F -100o F

700o F -100o F

+700o F – (-100o) = 800o F

So Mercury ranges nearly 800o F between daytime and nighttime.

Mercury Statistics

Mass (kg) 3.303e+23 Mass (Earth = 1) 5.5271e-02 Equatorial radius (km) 2,439.7 Equatorial radius (Earth = 1) 3.8252e-01 Mean density (gm/cm^3) 5.42 Mean distance from the Sun (km) 57,910,000 Mean distance from the Sun (Earth = 1) 0.3871 Rotational period (days) 58.6462 Orbital period (days) 87.969 Mean orbital velocity (km/sec) 47.88 Orbital eccentricity 0.2056 Tilt of axis (degrees) 0.00 Orbital inclination (degrees) 7.004 Equatorial surface gravity (m/sec^2) 2.78 Equatorial escape velocity (km/sec) 4.25 Visual geometric albedo 0.10 Magnitude (Vo) -1.9 Mean surface temperature 179°C Maximum surface temperature 427°C Minimum surface temperature -173°C Atmospheric composition Helium 42%Sodium 42%Oxygen 15%Other 1%

Mercury

the terrestrial planets. earth mars venus mercury because the 4 inner planets have solid, rocky...

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