The Terrestrial Planets

Because the 4 inner planets have solid, rocky terrains… Earth Venus Mars Mercury Because the 4 inner planets have solid, rocky terrains…

…they are sometimes called the “terrestrial planets”. Earth Venus Mars Mercury …they are sometimes called the “terrestrial planets”.

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

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?

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) At its greatest elongation…

…Mercury is never found more than 28o away from the Sun. greatest elongation (aphelion) …Mercury is never found more than 28o away from the Sun.

At its least elongation… least elongation (perihelion) At its least elongation…

…Mercury is only found at 18o away from the Sun. least elongation (perihelion) 18o …Mercury is only found at 18o away from the Sun.

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.

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

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

Mercury’s distance, on the other hand…

is found at only 0.39 AUs from the Sun.

This makes Mercury 2.5x closer to the Sun than the Earth. 1.00 AU _______ = 2.5 x closer 0.39 AU 0.39 AU This makes Mercury 2.5x closer to the Sun than the Earth.

In being 2.5x closer to the Sun, the Sun appears to be 6.25x bigger. 0.39 AU 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 If this is how big the Sun appears when viewed from Earth…

The Sun as seen from Mercury The Sun as seen from Earth 6.25 x bigger …then here’s how big the Sun appears when viewed from Mercury.

Rotation and Revolution

North Pole Mercury equator rotation: counter-clockwise

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.

Identical radio waves leave the dish with the same wavelengths.

From the approaching side, the returning waves are shorter.

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

From the receding side, however, the returning waves are longer. blue-shifted From the receding side, however, the returning waves are longer.

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

It’s the amount of red and blue shift… red-shifted blue-shifted It’s the amount of red and blue shift…

…which determines Mercury’s rate of rotation. red-shifted blue-shifted …which determines Mercury’s rate of rotation.

The faster Mercury rotates on its axis… red-shifted blue-shifted The faster Mercury rotates on its axis…

…the more red and blue shift will be observed. red-shifted blue-shifted …the more red and blue shift will be observed.

The slower Mercury rotates on its axis… red-shifted blue-shifted The slower Mercury rotates on its axis…

…the less red and blue shift red-shifted blue-shifted …the less red and blue shift will be observed.

Mercury revolves the Sun in only 88 days. Revolution 00.00 Days Mercury revolves the Sun in only 88 days.

Mercury revolves the Sun in only 88 days. Revolution 05.50 Days Mercury revolves the Sun in only 88 days.

Mercury revolves the Sun in only 88 days. Revolution 11.00 Days Mercury revolves the Sun in only 88 days.

Mercury revolves the Sun in only 88 days. Revolution 16.50 Days Mercury revolves the Sun in only 88 days.

Mercury revolves the Sun in only 88 days. Revolution 22.00 Days Mercury revolves the Sun in only 88 days.

Mercury revolves the Sun in only 88 days. Revolution 29.50 Days Mercury revolves the Sun in only 88 days.

Mercury revolves the Sun in only 88 days. Revolution 33.00 Days Mercury revolves the Sun in only 88 days.

Mercury revolves the Sun in only 88 days. Revolution 38.50 Days Mercury revolves the Sun in only 88 days.

Mercury revolves the Sun in only 88 days. Revolution 44.00 Days Mercury revolves the Sun in only 88 days.

Mercury revolves the Sun in only 88 days. Revolution 49.50 Days Mercury revolves the Sun in only 88 days.

Mercury revolves the Sun in only 88 days. Revolution 55.00 Days Mercury revolves the Sun in only 88 days.

Mercury revolves the Sun in only 88 days. Revolution 60.50 Days Mercury revolves the Sun in only 88 days.

Mercury revolves the Sun in only 88 days. Revolution 66.00 Days Mercury revolves the Sun in only 88 days.

Mercury revolves the Sun in only 88 days. Revolution 71.50 Days Mercury revolves the Sun in only 88 days.

Mercury revolves the Sun in only 88 days. Revolution 77.00 Days Mercury revolves the Sun in only 88 days.

Mercury revolves the Sun in only 88 days. Revolution 82.50 Days Mercury revolves the Sun in only 88 days.

Mercury revolves the Sun in only 88 days. Revolution Days Days 88.00 Mercury revolves the Sun in only 88 days.

Mercury rotates on its axis with a sidereal period of 59 days. Sidereal Rotation 00.00 Days Mercury rotates on its axis with a sidereal period of 59 days.

Mercury rotates on its axis with a sidereal period of 59 days. Sidereal Rotation 07.38 Days Mercury rotates on its axis with a sidereal period of 59 days.

Mercury rotates on its axis with a sidereal period of 59 days. Sidereal Rotation 14.75 Days Mercury rotates on its axis with a sidereal period of 59 days.

Mercury rotates on its axis with a sidereal period of 59 days. Sidereal Rotation 22.12 Days Mercury rotates on its axis with a sidereal period of 59 days.

Mercury rotates on its axis with a sidereal period of 59 days. Sidereal Rotation 29.50 Days Mercury rotates on its axis with a sidereal period of 59 days.

Mercury rotates on its axis with a sidereal period of 59 days. Sidereal Rotation 36.88 Days Mercury rotates on its axis with a sidereal period of 59 days.

Mercury rotates on its axis with a sidereal period of 59 days. Sidereal Rotation 44.25 Days Mercury rotates on its axis with a sidereal period of 59 days.

Mercury rotates on its axis with a sidereal period of 59 days. Sidereal Rotation 51.63 Days Mercury rotates on its axis with a sidereal period of 59 days.

Mercury rotates on its axis with a sidereal period of 59 days. Sidereal Rotation 59.00 Days Mercury rotates on its axis with a sidereal period of 59 days.

Mercury rotates on its axis with a sidereal period of 59 days. Sidereal Rotation Days pointing upward 59.00 Mercury rotates on its axis with a sidereal period of 59 days.

Mercury’s noon-to-noon, however, requires 176 days to complete. Synodic Rotation Days 000.00 Mercury’s noon-to-noon, however, requires 176 days to complete.

Mercury’s noon-to-noon, however, requires 176 days to complete. Synodic Rotation 007.36 Days Mercury’s noon-to-noon, however, requires 176 days to complete.

Mercury’s noon-to-noon, however, requires 176 days to complete. Synodic Rotation 014.75 Days Mercury’s noon-to-noon, however, requires 176 days to complete.

Mercury’s noon-to-noon, however, requires 176 days to complete. Synodic Rotation 022.12 Days Mercury’s noon-to-noon, however, requires 176 days to complete.

Mercury’s noon-to-noon, however, requires 176 days to complete. Synodic Rotation 029.50 Days Mercury’s noon-to-noon, however, requires 176 days to complete.

Mercury’s noon-to-noon, however, requires 176 days to complete. Synodic Rotation 036.88 Days Mercury’s noon-to-noon, however, requires 176 days to complete.

Mercury’s noon-to-noon, however, requires 176 days to complete. Synodic Rotation 044.25 Days Mercury’s noon-to-noon, however, requires 176 days to complete.

Mercury’s noon-to-noon, however, requires 176 days to complete. Synodic Rotation 051.63 Days Mercury’s noon-to-noon, however, requires 176 days to complete.

Mercury’s noon-to-noon, however, requires 176 days to complete. Synodic Rotation 059.00 Days Mercury’s noon-to-noon, however, requires 176 days to complete.

Mercury’s noon-to-noon, however, requires 176 days to complete. Synodic Rotation 066.37 Days Mercury’s noon-to-noon, however, requires 176 days to complete.

Mercury’s noon-to-noon, however, requires 176 days to complete. Synodic Rotation 073.74 Days Mercury’s noon-to-noon, however, requires 176 days to complete.

Mercury’s noon-to-noon, however, requires 176 days to complete. Synodic Rotation 081.11 Days Mercury’s noon-to-noon, however, requires 176 days to complete.

Mercury’s noon-to-noon, however, requires 176 days to complete. Synodic Rotation 088.00 Days Mercury’s noon-to-noon, however, requires 176 days to complete.

Mercury’s noon-to-noon, however, requires 176 days to complete. Synodic Rotation 095.36 Days Mercury’s noon-to-noon, however, requires 176 days to complete.

Mercury’s noon-to-noon, however, requires 176 days to complete. Synodic Rotation 102.24 Days Mercury’s noon-to-noon, however, requires 176 days to complete.

Mercury’s noon-to-noon, however, requires 176 days to complete. Synodic Rotation 111.12 Days Mercury’s noon-to-noon, however, requires 176 days to complete.

Mercury’s noon-to-noon, however, requires 176 days to complete. Synodic Rotation 118.00 Days Mercury’s noon-to-noon, however, requires 176 days to complete.

Mercury’s noon-to-noon, however, requires 176 days to complete. Synodic Rotation 123.63 Days Mercury’s noon-to-noon, however, requires 176 days to complete.

Mercury’s noon-to-noon, however, requires 176 days to complete. Synodic Rotation 131.25 Days Mercury’s noon-to-noon, however, requires 176 days to complete.

Mercury’s noon-to-noon, however, requires 176 days to complete. Synodic Rotation 138.90 Days Mercury’s noon-to-noon, however, requires 176 days to complete.

Mercury’s noon-to-noon, however, requires 176 days to complete. Synodic Rotation 146.50 Days Mercury’s noon-to-noon, however, requires 176 days to complete.

Mercury’s noon-to-noon, however, requires 176 days to complete. Synodic Rotation 154.12 Days Mercury’s noon-to-noon, however, requires 176 days to complete.

Mercury’s noon-to-noon, however, requires 176 days to complete. Synodic Rotation 161.75 Days Mercury’s noon-to-noon, however, requires 176 days to complete.

Mercury’s noon-to-noon, however, requires 176 days to complete. Synodic Rotation 169.38 Days Mercury’s noon-to-noon, however, requires 176 days to complete.

Mercury’s noon-to-noon, however, requires 176 days to complete. Synodic Rotation 176.00 Days Mercury’s noon-to-noon, however, requires 176 days to complete.

Mercury’s noon-to-noon, however, requires 176 days to complete. Synodic Rotation Days 176.00 noon Mercury’s noon-to-noon, however, requires 176 days to complete.

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

is exactly twice as long as its year. 176 days = (88 days) x 2 Its noon-to-noon is exactly twice as long as its year.

Notice also that the 176-day synodic rotation…

…is exactly equal to 3 sidereal rotations. 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.

000.00 Day Counter Sidereal Revolution Synodic

007.38 Day Counter Sidereal Revolution Synodic

014.78 Day Counter Sidereal Revolution Synodic

022.15 Day Counter Sidereal Revolution Synodic

029.52 Day Counter Sidereal Revolution Synodic

036.89 Day Counter Sidereal Revolution Synodic

044.26 Day Counter Sidereal Revolution Synodic

051.63 Day Counter Sidereal Revolution Synodic

Day Counter 059.00 Sidereal Revolution Synodic

Day Counter 059.00 Sidereal Revolution Synodic

Day Counter 059.00 1 Sidereal Revolution Synodic

059.00 1 After 59 days in orbit, Day Counter Sidereal Revolution Revolution Synodic After 59 days in orbit,

After 59 days in orbit, Mercury completes 1 sidereal day. Day Counter 059.00 1 Sidereal Revolution Synodic After 59 days in orbit, Mercury completes 1 sidereal day.

Day Counter 059.00 1 Sidereal Revolution Synodic

066.37 Day Counter 1 Sidereal Revolution Synodic

073.74 Day Counter 1 Sidereal Revolution Synodic

081.11 Day Counter 1 Sidereal Revolution Synodic

Day Counter 088.00 1 Sidereal Revolution Synodic

088.00 1 After 88 days in orbit, Day Counter Sidereal Revolution Revolution Synodic After 88 days in orbit,

After 88 days in orbit, Mercury completes 1 revolution. Day Counter 088.00 1 Sidereal Revolution Synodic After 88 days in orbit, Mercury completes 1 revolution.

After 88 days in orbit, Mercury completes 1 revolution. Day Counter 088.00 1 Sidereal Revolution Synodic After 88 days in orbit, Mercury completes 1 revolution.

After 88 days in orbit, Mercury completes 1 revolution. Day Counter 088.00 1 Sidereal 1 Revolution Synodic After 88 days in orbit, Mercury completes 1 revolution.

Day Counter 088.00 1 Sidereal 1 Revolution Synodic

096.36 Day Counter 1 Sidereal Revolution Synodic

103.24 Day Counter 1 Sidereal Revolution Synodic

111.12 Day Counter 1 Sidereal Revolution Synodic

118.00 Day Counter 1 Sidereal Revolution Synodic

118.00 1 After 118 days in orbit, Day Counter Sidereal Revolution 1 Sidereal Revolution Synodic After 118 days in orbit,

After 118 days in orbit, Mercury completes 2 sidereal days. 118.00 Day Counter 1 Sidereal Revolution Synodic After 118 days in orbit, Mercury completes 2 sidereal days.

After 118 days in orbit, Mercury completes 2 sidereal days. 118.00 Day Counter 1 Sidereal Revolution Synodic After 118 days in orbit, Mercury completes 2 sidereal days.

After 118 days in orbit, Mercury completes 2 sidereal days. 118.00 Day Counter 2 1 Sidereal Revolution Synodic After 118 days in orbit, Mercury completes 2 sidereal days.

118.00 Day Counter 2 1 Sidereal Revolution Synodic

123.63 Day Counter 2 1 Sidereal Revolution Synodic

131.25 Day Counter 2 1 Sidereal Revolution Synodic

138.90 Day Counter 2 1 Sidereal Revolution Synodic

145.50 Day Counter 2 1 Sidereal Revolution Synodic

154.12 Day Counter 2 1 Sidereal Revolution Synodic

161.75 Day Counter 2 1 Sidereal Revolution Synodic

169.38 Day Counter 2 1 Sidereal Revolution Synodic

Day Counter 176.00 2 Sidereal 1 Revolution Synodic

176.00 2 1 After 176 days in orbit, Day Counter Sidereal Revolution Synodic After 176 days in orbit,

After 176 days in orbit, 3 things happen with Mercury. Day Counter 176.00 2 Sidereal 1 Revolution Synodic After 176 days in orbit, 3 things happen with Mercury.

Day Counter 176.00 2 Sidereal 1 Revolution Synodic

Day Counter 176.00 2 Sidereal 1 Revolution Synodic Mercury achieves

Mercury achieves its third sidereal day. Day Counter 176.00 2 Sidereal 1 Revolution Synodic Mercury achieves its third sidereal day.

Mercury achieves its third sidereal day. Day Counter 176.00 2 Sidereal 1 Revolution Synodic Mercury achieves its third sidereal day.

Mercury achieves its third sidereal day. Day Counter 176.00 3 Sidereal 1 Revolution Synodic Mercury achieves its third sidereal day.

Day Counter 176.00 3 Sidereal 1 Revolution Synodic

Day Counter 176.00 3 Sidereal 1 Revolution Synodic It also completes

It also completes 2 revolutions around the Sun. Day Counter 176.00 3 Sidereal 1 Revolution Synodic It also completes 2 revolutions around the Sun.

It also completes 2 revolutions around the Sun. Day Counter 176.00 3 Sidereal 1 Revolution Synodic It also completes 2 revolutions around the Sun.

It also completes 2 revolutions around the Sun. Day Counter 176.00 3 Sidereal 2 Revolution Synodic It also completes 2 revolutions around the Sun.

Day Counter 176.00 3 Sidereal 2 Revolution Synodic

176.00 3 2 And at the same time, Day Counter Sidereal Revolution Synodic And at the same time,

And at the same time, Mercury also completes 1 synodic day. Day Counter 176.00 3 Sidereal 2 Revolution Synodic And at the same time, Mercury also completes 1 synodic day.

And at the same time, Mercury also completes 1 synodic day. Day Counter 176.00 3 Sidereal 2 Revolution Synodic And at the same time, Mercury also completes 1 synodic day.

And at the same time, Mercury also completes 1 synodic day. Day Counter 176.00 3 Sidereal 2 Revolution 1 Synodic And at the same time, Mercury also completes 1 synodic day.

Day Counter 176.00 3 Sidereal 2 Revolution 1 Synodic

176.00 3 2 1 Since the number “176” Day Counter Sidereal Revolution Synodic Since the number “176”

Since the number “176” is a multiple of both “88” and “59”… Day Counter 176.00 3 Sidereal 2 Revolution 1 Synodic Since the number “176” is a multiple of both “88” and “59”…

Day Counter 176.00 3 Sidereal 2 Revolution 1 Synodic

…then all 3 of these numbers Day Counter 176.00 3 Sidereal 2 Revolution 1 Synodic …then all 3 of these numbers

…then all 3 of these numbers changed on exactly the same day. Day Counter 176.00 3 Sidereal 2 Revolution 1 Synodic …then all 3 of these numbers changed on exactly the same day.

…then all 3 of these numbers changed on exactly the same day. Day Counter 176.00 3 Sidereal 2 Revolution 1 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.

The surrounding crust consists of silicate rock. rocky crust iron-nickel core The surrounding crust consists of silicate rock.

Mercury’s rocky crust is nearly 700 km thick. iron-nickel core 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.

Curved cliffs, probably formed when Mercury shrank while cooling down Lobate Scarps Curved cliffs, probably formed when Mercury shrank while cooling down

The Plains of Mercury No 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

resembles the surface of the Moon. The surface of Mercury resembles the surface of the Moon.

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

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

Both bodies are heavily cratered. Moon Mercury Both bodies are heavily cratered.

Both bodies are similar in size and appearance. Moon Mercury Both bodies are similar in size and appearance.

And neither body has an atmosphere. Moon Mercury And neither body has an atmosphere.

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 If this was your guess, then you were correct.

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

Surface Temperature

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

Its daytime temperature can reach 700o Fahrenheit.

And its nighttime temperature can reach -100o Fahrenheit.

All planets without atmospheres get very cold at night. 700o F -100o F All planets without atmospheres get very cold at night.

But because Mercury is so close to the Sun… 700o F -100o F But because Mercury is so close to the Sun…

…its daytime temperatures exceed those of all other planets.

So Mercury ranges nearly 800o F between daytime and nighttime. +700o F – (-100o) = 800o F 700o F -100o F So Mercury ranges nearly 800o F between daytime and nighttime.

Mercury 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% The southwest quadrant of Mercury is seen in this image taken March 29, 1974, by the Mariner 10 spacecraft. The picture was taken four hours before the time of closest approach when Mariner was 198,000 km (122,760 mi) from the planet. The largest craters seen in this picture are about 100 km (62 mi) in diameter. Mercury has been visited by only one spacecraft, Mariner 10. It flew by three times in 1974 and 1975. Only 45% of the surface was mapped (and, unfortunately, it is too close to the Sun to be safely imaged by HST). A new discovery-class mission to Mercury, MESSENGER was launched by NASA in 2004 and will orbit Mercury starting in 2011 after several flybys.