Our Planetary System - Terrestrial Planets






Earth

Earth has a density that is higher than both water and rock. Because of this, we know that the interior of the Earth must be much much denser.

Geologists use the way that P waves and S waves travel through the Earth by studying the shadow zones to determine the interior of the Earth.

P waves, or pressure waves, compress and expand in order to travel. S waves, or shear waves, move side ways. During an earthquake, P Waves go out first, followed by S waves. Because S waves do not travel through liquids, we can study how the waves travel and bend as they go through the Earth to understand the medium that is the inner Earth.

The greenhouse effect is where infrared radiation is absorbed by water vapor and carbon dioxide, trapping it within the atmosphere, warming the air and surface.

Differentiation shows that at some point in the past, the Earth was a hot molten place. The denser material sunk down to the core, and the lesser dense material was pushed up.

Radioactivity allows us to determine the Earthís age through isotope half lives. Because we know the half life, or amount of time for half of a sample of isotopes to breakdown into something else, we can take a sample of rock, and radioactively date it.

As the heavy elements broke up through radioactive decay, they released energy and heat. This heated up the Earth, because there were a lot of the atoms back in the early days of the Earth. This lasted about 700 million years, until the Earthís crust cooled and solidified.

Surface mountains, oceanic trenches, and other large-scale features on Earthís surface are caused by plate tectonics Ė the motion of the Earthís plates caused by convection under the Earthís surface.

Quasars never show any measurable apparent motion in the sky from their movement in space. Therefore, after accounting for the Earthís motion in space, any apparent motion of a quasar must be caused by movement of the telescope viewing the quasar. This apparent motion is used in monitoring the movement of the tectonic plates.

Both rapid rotation and a conducting liquid are needed to create a dynamo. In the Earthís core, this creates the Earthís magnetosphere..

The Earthís magnetosphere is the magnetic field lines that surround the Earth in a teardrop shape. It protects Earth from the harshness of space, with particles of energy carried by the solar winds that can break electronic devices, and cause issues for life on Earth. It wasnít discovered until the 19050s by satellites.

As plates move around, the rocks ďrecordĒ the magnetic field lines present at the time that they move from the interior to the crust. By studying these rocks, we can see how the magnetic field lines have changed over time. The reversal of the magnetic field lines probably aided in the spreading of the sea floor, causing people and animals in various areas to evolve differently (when we were all on Pangea, we probably evolved the same). Also, the brief moments of reversal may have allowed for some of the particles from the solar winds to penetrate to the Earth, and affect life on the planet.

Because of the gravitational effect that the Earth has on the Moon, it would cause high tide to the side facing the Earth, and away from the Earth, on the Moon. On Earth, we get two high tides and low tides a day due to the rotation of the Earth. However, since only one side of the Moon ever faces the Earth, the high and low tides would always be in the same place. Since the Earth has a stronger pull than the Moon does, the tides would be much higher on the Moon than on Earth.

Without the Moon, we would still have tides. The Sun also has an effect on the Earth, pulling on it, and causing tides. They would not be as pronounced as they are due to the Moon.

The greenhouse effect is helpful in that it warms the Earth, and keeps it from being too cold. Itís similar to how a greenhouse keeps plants warm so that they can grow. Like with anything, however, too much of a good thing is bad. With a runaway greenhouse, temperatures rise too much, and it gets too hot for life. To get an idea of how bad it can get, look to Venus. Thereís no naked women and garden of eden, thereís just hot hot hot melting lead hot. Definitely not a place Iíd want to be.

The troposphere is the part of the atmosphere in which convection occurs.

The oxygen in Earthís atmosphere is the result of the appearance of life on our planet.

Sunlight is absorbed by Earthís surface and then reemitted in the form of infrared (heat) energy.

It is impossible to drill into the interior of the Earth. Once you get down a few km (about 10), the material is so dense that not even diamond can cut through it.

Earthís core temperature is comparable to the surface temperature of the Sun.

When plates collide, they either push each other up, push each other down, or one slides under the other.

Earthís magnetic field is not due to a permanently magnetized iron core. It is continually regenerating from a spinning partially liquid iron core.

An aurora occurs when trapped electrons and protons in the magnetosphere collide with the upper atmosphere.

At any given coastal location on Earth, there are two high and low tides each day.

Tides are caused by the gravitational pull of the Moon and the Sun on Earth.

If you were making a scale model of Earth representing our planet by a 12-inch basketball, the inner core would be about the size of a 2-inch golf ball.

If there were significantly more greenhouse gases, such as CO2 in Earthís atmosphere, then Earthís average temperature would change.

The deepest that geologists have drilled into Earth is about the same as the altitude most commercial jet airplanes fly.

Due to plate tectonics, the width of the Atlantic Ocean is separating at a rate about the same as the growth of human fingernails.

At Earthís geographic North Pole, a magnetic compass needle would point (approximately) toward Kansas City.

Which of the following statements is true? Because of the tides, the Moon is spiraling away from Earth.

The Moon and Mercury

During the Apollo missions, mirrors were placed on the Moon. By bouncing lasers off of these mirrors, and timing them, we can accurately calculate the distance to the Moon.

Because of how close Mercury is to the Sun, it is usually hidden by the Sunís light. Itís only for a little after sunset, or just before sunrise that it is generally visible (depending on which side of the Sun it is on).

The Moon and Mercury have low escape speeds. Because the lighter molecules, such as hydrogen, move so quickly, they are easily able to travel at speeds faster than the escape speeds of these planets. Because of this, all of the molecules have left the bodies and they do not have atmospheres.

Lunar maria are the dark spots on the Moon. Originally, they were thought to be seas on the Moon. In a sense, they are, because of how they form. They are the result of lava flows from the interior of the Moon. So in a way, they are ďlava seasĒ.

The Moon is in synchronous orbit around the Earth because one face of the Moon always faces the Earth. This is due to the rotation period of the Moon (27.3 days) being the same as the orbital period of the Moon.

Scarps are cliffs on Mercuryís surface, believed to have formed as the planet cooled and the surface shrunk, much like an old apple will get deformed as it withers with age. As there are no scarps that have been hit by meteorites, they are believed to have formed after the meteoric bombardment.

Meteoritic bombardment is the primary source of current lunar erosion. It is much less than Earthís erosion because the Moon is smaller, and therefore, cooled much quicker because the interior (on average) is closer to the surface. Because the Moon cooled so quickly, there is no more volcanic activity, and therefore, no more erosion caused by it Ė thus it is eroding much slower than Earth.

Lunar Prospector probe found trillions of tons of ice on the lunar poles, hidden from the Sun in craters near the lunar poles.

By studying the rocks from the highlands and maria, the different compositions can be compared. Loosely speaking, the composition of the highlands is that of the crust while the maria is that of the mantle. The maria rose from the inner mantle up to the crust, so the highland rock is older. Also, radioactive dating on the rocks show that the highlands are about a billion years older than rocks from the maria.

Both the Moon and Mercury were the scenes of heavy meteoric bombardment. This is why they both have craters on their surfaces. The lunar highlands were caused by volcanic activity, where as the scarps on Mercury were caused by the core cooling and shrinking.

The current theory of the formation of the Moon is that a large object, about the size of Mars, collided with the Earth during its formative years. This caused a large amount of material to be blown off into orbit around the Earth. As the Earth cooled, this material also cooled, condensing into the Moon.

Although one side of the moon always faces Earth, the side of Earth facing the Moon changes. Thus, someone on the Moon facing the Earth will see the Earth rotating in the sky. Also as the Moon is orbiting the Earth, the position of the Sun changes. Therefore, youíll see the Earth go through phases.

(Where on the Moon would be the best place to make astronomical observations: No direct answer Ė but, the far side would block out Earthshine, but could have problems when the far side is the lighted side (staring straight into the Sun). Possibly the poles, where thereís little direct light, and can block out most Earthshine). This is better than observations on Earth, as the Earthís atmosphere can obstruct certain wavelengths of electromagnetic radiation. From the Moon, you can observe everything.

Mercury is never seen at midnight because it is so close to the Sun. At midnight, the Sun is on the other side of the planet. Therefore, itís not visible.

On the side that faces the Earth, the lava in the mantle of the Moon was pulled up to the surface, forming the maria and causing the crust to be thinner in these areas.

Laser ranging can determine the distance to the moon to an accuracy of a few centimeters.

Mercury can never be seen at midnight.

Mercuryís solar day is longer than its solar year.

The most accurate method for determining the distance to the Moon is by lasers bouncing off mirrors, not by parallax.

Mercuryís daytime temperature is higher than the Moonís because mercury is closer to the Sun.

Craters on the Moon and Mercury are primarily the result of meteoritic bombing.

There is no volcanic activity today on the surface of the Moon.

Although daytime temperatures on the Moon and Mercury are very high, it may still be possible for those two bodies to have large amounts of water ice at their poles.

The lunar mariaís dark, dense rock originally was part of the lunar mantle.

The most likely scenario for the formation of the moon is a collision between Earth and another planet-sized body.

In relation to the density of Earthís Moon, Mercuryís density suggests that the planet has a dense metal core.

Every two times Earthís Moon rotates on its axis, it orbits Earth exactly two times.

Planets and moons showing the most craters have the oldest surfaces.

The most likely theory of the formation of Earthís Moon is that it formed from a collision of Earth with a Mars-sized object.

Mercury, being smaller than Mars, probably cooled and solidified faster, because it is smaller.

Venus

Because Venus orbits between the Earth and the Sun, it can only be viewed when it is close to the Sun.

There appears to be a discrepancy of about 3 hours in 584 days in the 5:1 resonance of Venus, so that thereís actually no true resonance.

The nearly 5:1 resonance between Venusís rotation and orbit means that almost always the same face of Venus faces Earth at its closest approach.

The current explanation of why Venus spins slowly and backwards is due to something hitting it during its early formation.

Because the clouds cover Venus, and they are so thick, you would not be able to see into space from Venus, so would not be able to see Earth. Not to mention that when you are there, you would be crushed by the atmosphere, and burned up by the heat.

Ultraviolet images returned by Pioneer Venus show about that the high-level clouds are composed of sulfuric acid drops.

The atmosphere of Venus is almost entirely carbon dioxide and nitrogen. The clouds are composed of sulfuric acid.

The water that Venus had turned to water vapor, and broke up in the atmosphere. This caused more carbon dioxide in the atmosphere than what we have on Earth. Part of why we donít have as much is because of plant life on the planet, breathing in the carbon dioxide, and releasing oxygen into the atmosphere. Venus never had life appear, so there was nothing to get rid of the carbon dioxide.

Had Venus formed at Earthís distance, it probably would be a twin to Earth. The runaway greenhouse effect would not have happened, because the water would not have turned to water vapor, and been broken up in the atmosphere, thus causing the runaway greenhouse we see today on the planet.

The elevated continents of Venus only take up about 8% of the planetís surface area, while on Earth they make up 25%.

Because of the thickness of the atmosphere, smaller meteors cannot get through. Therefore, there are no impact craters smaller than about 2 to 3 km across, and very few smaller than 25 km in diameter.

The surface of Venus appears to be relatively young. It has been resurfaced by volcanism within the past few hundred million years.

Venus has surface features that resemble those on Earth caused by volcanoes. Venus has many lava domes and shield volcanoes.

Defining life as we know it, it is impossible for Venus to support it. The temperatures are way too hot, and the atmosphere is completely inhospitable for it.

To the effect that Venus has suffered, Earth will not have as bad a runaway greenhouse effect. Even if we ended up with an atmosphere as bad as Venusís, our distance from the Sun helps to keep us from getting quite that hot.

Venus does not have a retrograde orbit about the Sun, but does rotate the opposite direction.

Venus appears brightest when it is at about 39 degrees from the Sun. At full, itís on the other side of the Sun, and is not visible.

Venus has been mapped by radar from both Earth and satellites.

Venusís atmosphere is not at all like Earthís.

Venus has roughly the same temperature at its equator as at its poles.

Venus does not appear to have tectonic activity as there is on Earth.

Evidence of lava flows is common on the surface of Venus.

Venusís mass has been accurately measured by orbiting spacecraft.

Most craters on the surface of Venus are the result of volcanism.

The greenhouse effect in the early atmosphere of Venus was most likely intensified by the presence of water vapor.

Venusís permanent retrograde rotation about its axis results in the planet having its north pole below the plane of the ecliptic.

Venusís surface is permanently obscured by clouds. As a result, the surface has been studied primarily by orbiting satellites using radar.

Compared with Earth, Venus has a level of plate tectonic activity that is virtually non-existent.

Compared with Earthís atmosphere, most of Venusís atmosphere is spread out much farther from the surface.

Carbon dioxide on Venus is all in the atmosphere.

Mars

Mars is largest and brightest at opposition. This can be as close as 0.37 AU.

Because of Marsís very eccentric orbit, the opposition can range from as close as .37AU to as much as about .6 AU.

What was once thought to be canals are actually cratered and eroded areas.

For the most part, the weather on Mars does not vary. There is surface heating from the Sun, light winds, and then the Sun sets and the temperature goes down. In the southern hemisphere during the summer, however, the routine changes. Strong winds sweep up dusts, causing dust storms that flood the atmosphere with dust, making storms that are worse than we can imagine on Earth.

The polar caps are composed primarily of carbon dioxide frost (dry ice). Each is composed of a seasonal cap and a residual cap. The two caps do not have the same maximum size due to the eccentricity of Marsís orbit (southern is about 4 times bigger). Seasonal caps are composed entirely of carbon dioxide. The northern residual cap is much larger than the southern cap.

Martian surface has vast plains, huge volcanoes, deep channels and canyons. The major feature is the Tharsis bulge. Associated with this are Olympus Mons (largest known volcano in the solar system) and a huge crack called Valles Marineris.

Mars has a very thin atmosphere, with a density of less than 1% that of the Earthís. It is primarily composed of carbon dioxide. Because of these two facts, itís impossible to breathe on Mars.

Runoff channels (remains of ancient Martian rivers) and outflow channels (the paths taken by flash floods that went from the southern highlands into the northern plains) are evident that Mars had water in the past.

There is no liquid water on Mars today. The water is locked up in the polar caps, and in permafrost under the Martian surface.

There is water on Mars today, in the polar caps and permafrost layer under the surface.

The masses of Marsís moons was measured by the gravitational effect they had on the Viking orbiters. The measurements showed that they are far less dense than any world we have yet encountered, leading astronomers to believe that they are captured asteroids.

The presence of iron on the surface of Mars suggests that Mars never melted as extensively as Earth did, and therefore it did not undergo complete differentiation.

Earth from Mars would appear much as Venus appears to us. Because Earth is within the orbit of Mars, it will go through phases as viewed from Mars.

If humans were sent to mars to live, the lack of an atmosphere would have to be considered. In addition, the strong winds and dust storms during the southern hemisphere summer could pose hazards to the humans. About the only thing we may be able to get from Mars would be water from the permafrost layer under the Martian surface. However, pretty much everything we would need would have to be brought with us.

Although Marsís atmosphere is primarily a greenhouse gas, it does not suffer the greenhouse effect because it is far away from the Sun (and therefore does not receive as much heat energy from the Sun as Venus does, for example), and the atmosphere is very thin. Also, Mars has had very little volcanic activity (as compared to Earth). Therefore, the processes that are diminishing the carbon dioxide are doing so faster than it is being replenished.

Compare and contrast the evolution of the atmospheres of Mars, Venus and Earth: Instead of Earth's atmosphere exhibiting a stable greenhouse effect, or Venus' atmosphere providing too dominate of a greenhouse effect making it extremely hot, the presence of liquid water on Mars would have caused much of the atmospheric carbon dioxide to have dissolved in Martian rivers and lakes to ultimately combine with Martian surface rocks. Like Earth, Mars CO2 may have been replenished by volcanism.

Seen from Mars, Earth would go through phases, just as Venus and Mercury do.

Mars has extremely strong surface winds that can reach hurricane speeds.

Seasonal changes in the appearance of Mars are caused by the large eccentricity of its orbit.

Olympus Mons is the largest volcano known on Mars.

There are no indications of past plate tectonics on Mars.

Valles Marineris is much larger than Earthís Grand Canyon.

The polar caps of Mars are composed predominantly of carbon dioxide frost.

The great height of Martian volcanoes is a direct result of the planetís low gravity.

NASAís Opportunity Rover did not detect liquid water just under the Martian surface.

Water once flowed on the surface of Mars.

Compared with the Earthís orbit, the orbit of Mars is more eccentric.

Compared with Earthís diameter, the diameter of Mars is significantly smaller.

In terms of area, the extinct Martian volcano Olympus Mons is about the size of Colorado.

Maps of Mars clearly shows cratered terrain in the south.

The best evidence for the existence of liquid water on an ancient Mars is Figure 10.12 in the northern lowlands.

In comparison to the atmosphere of Venus, the vastly different atmospheric character of Mars is likely due to a reverse greenhouse effect.