Terrestrial Planets General Information Mercury diameter 4880 km

Terrestrial Planets

General Information • • • Mercury diameter = 4880 km, no atmosphere Venus diameter = _______ km, atmosphere Earth diameter = 12800 km, atmosphere Mars diameter = _____ km, atmosphere Size and the distance from the Sun are responsible for the differences in the atmospheres on each planet.

Lore behind Mercury • Named after the Messenger of the gods. • It orbits around the Sun quickly. • Moves across the sky quickly.

Mercury • • • The smallest terrestrial planet Similar in size and mass to our moon. Has a mass of 1/20 th of the Earth. Mercury lacks an atmosphere Earlier we discussed the importance of Surface gravity and the presence of an atmosphere. • Does anyone notice a discrepancy regarding terrestrial planets, size, and the presence of an atmosphere?

What is the deal with Mars? • • Mercury is small, Mars is less than 2, 000 km larger. Mercury has no atmosphere – Mars does! Mars is half as big as Earth and its mass is 1/10 th Why does it have an atmosphere and not Mercury? – There is no significant difference in surface gravity (mercury = 0. 38 mars = 0. 380 of Earth) – And they differ in mass by only. 02 – Mercury escape velocity = 4. 25 km/sec. – Mars escape velocity = 5. 03 km/sec – Earth escape velocity = 11. 3 km/sec

The answer lies in the distance from the Sun and Temperature • Mercury is VERY close to the Sun. – Its equatorial temperatures during the day reach 700 K (that is 800 F). – At night Temperatures drop dramatically to 100 K (-280 F). – The temperature is so great the molecules are moving so fast that they are able to escape into space. • In addition, because of the dramatic changes in temperature, IF any gas molecules were present, they would be forced to the poles and then frozen into ice. • Finally, Mercury shows little evidence of volcanic activity, which is thought to be necessary for an atmosphere to develop.

Mars on the other hand • Mars has volcanoes, which act as a source for gas. • Mars is farther from the Sun so the gases are not as hot and as a result do not move around as much. – The gas does not reach escape velocity. • Temperature variations are not as great so there is less movement of gas molecules.

Mercury • • • Hypothesized to have a silicate mantle A large iron-nickel core It is unknown if the core is liquid Mercury rotates very slowly The rotation could have been slowed by a collision with a large planetesimal. Fig 8. 8 • The slow rotation in combination with lack of movement of the core means a very weak magnetic field. • The Earth’s magnetic field manifests itself with a compass.

Resonance and a Mercury Day • Mercury rotates so slowly that it spins three times for every 2 trips around the Sun. • Because of tidal forces from the Sun Mercury’s orbital speeds change. • Mercury’s orbit is elliptical and is closer to the sun at specific times. • This results in – When a force that is repeatedly applied causes an increase in motion.

Odd Fact • Because of Mercury’s odd rotation • A solar day is 176 Earth Days. • The Sun changes its direction of motion in the sky. • It will set and then reverse and then set again. See fig 8. 9

Venus • Most similar to the Earth in ____ and _____ • • Said to be Earth’s twin because of its size and proximity to Earth • However, its surface and atmosphere are very different. • The surface is covered with ______.

The atmosphere of Venus • • • 96% _________! 3. 5% Nitrogen The rest is a mix of water and other gases. The clouds are composed of Sulfuric Acid. The Sulfur compounds may have been ejected from volcanoes and combined with some of the water in the atmosphere to form the acid. • Major Greenhouse effect. • What is the Greenhouse effect?

Venus is easy to see • The clouds reflect large amounts of Sunlight • As a result it is a large bright object in the sky. • You do not even need a telescope to see it.

Venus and Temperature • It is about 750 K – 900 F • The temperature is a result of greenhouse effect. • The atmosphere ranges from the surface to over 40 km up and continues to about 140 km • The atmospheric temperature drops because the concentration of CO 2 drops at higher altitudes. At 40 km up the temperature is near room temperature (300 K)

Venus topography • No oceans • Just lowlands and highlands • The Highlands are mountainous and similar to the continents. There are only 2 on Venus. • Venus is volcanically active • Some of the differences between the Earth and Venus can be explained by the amount of water molecules in the rock.

Water and rocks • The amount of water in rock affects how the rock melts during volcanic activity. • It also affects how the rock and lava retain heat. • The more heat the rock retains the more volcanic activity and shifts in the crust are possible.

Rotation of Venus • Venus spins very slowly and in the opposite direction of other planets. • Because it spins backwards it is said to have retrograde rotation. • As a result, the Sun rises in the west and sets in the East. • It takes 243 days to make one rotation. • Its slow rotation results in no magnetism.

Two hypotheses regarding retrograde rotation. • A large planetesimal crashed into Venus when it was first formed. • This slowed the rotation and tilted its axis • A second theory is that tidal effects from the Sun and Earth altered the tilt angle. • By changing the tilt angle, the rotation of the planet was reversed and slowed.

Mars • The planet that has gotten more attention than any other except Earth. • Named after the Roman god of _____. • Appears almost blood red (hence the name). • Temperature rarely gets _________. • Surface gravity is much less if you weigh 100 lbs. on earth, you would weigh _______ lbs on mars • Mars has ____ moons. ____ the largest, _____, the smaller of the two. • The Martian surface has some similarities to Earth’s.

Mars has been extensively studied • Here a few of the probes sent to take a peek at Mars: – Mariners – Vikings – Mars Global Surveyor – Pathfinder – Sojourner – Mars Rovers (2) Spirit and Opportunity

Martian atmosphere • Mostly CO 2 • Small amounts of – N, Ar, O, CO, Ne, Kr, Xe, H 2 O • Atmospheric clouds – made of pink dust, blue clouds of ice crystals, white clouds of water vapor. • The Earth’s atmosphere is mostly N. Clouds on Earth are mostly clouds of water vapor.

No Greenhouse Effect on Mars • The density of CO 2 and other gases in the Martian atmosphere is very low. That means there is not a lot of gas to start with. • Even though the atmosphere is 95% CO 2, there is not enough to cause a greenhouse effect. Thus Mars is still relatively cold. • Think of it this way which is greater 95% of 5 or (percentage of CO 2 in Earth atm. ). 05% of 500 • Ans. = 95% of 5 = 4. 75, . 05% 0 f 500 = 25.

Martian atmosphere (cont. ) • No rain because there is not enough water in the atmosphere to form precipitation. • There may be some frost and fog that condenses into ice. • There is frozen water at the poles and potentially underground. • It is believed that Mars may have had liquid water a few billion years ago. • There are two theories which explain why there is no more liquid water on Mars.

How Mars lost its water • The atmosphere is not dense enough to keep water in liquid form and on the surface. (evaporates without heat. Mars has a surface that has been freeze dried!) • Hypothesis 1: Mars had a dense atmosphere that kept liquid water present, but an asteroid struck the planet with such great force that some of the atmosphere was knocked off because of the weak surface gravity. • Without the atmosphere, the liquid water was lost. • The Earth may have had a similar collision that lead to the demise of the dinosaurs.

How Mars lost its water • Hypothesis 2 – The low surface gravity allowed the gases to gradually escape. Thus the atmosphere became less and less dense. • Volcanic activity slowed so less gas was released to replace the gases that were lost to space.

Martian surface • The Martian surface shows little evidence of erosion. • It is dusty, rocky, and dry. • Most of the dust is limonite, a red brick colored mineral that is found in some deserts on earth. • Composed of silicates and iron.

Martian surface features • • Mars is similar to Earth in many aspects: Immense canyons Old lava flows Ice caps which change in size due to seasonal changes.

Martian Surface • No indication of recent volcanic activity. • The core of Mars is most likely solid and not molten. • No tectonic activity. • Ice caps on poles made of dry ice (frozen CO 2) and frozen water. – The Southern cap is dry ice – The Northern cap has a thin layer of dry ice with a thicker layer of frozen water underneath.

Martian poles • The size of the polar caps changes with season. • Because of the tilt of the planet (similar to Earth) Mars has seasons. – During the winter the poles increase in size. – During the summer they decrease in size. • The layering of the polar caps indicates that there have been long term cyclical temperature patterns on Mars. – Similar to the ice ages of Earth

Martian Moons • Small and irregularly shaped • Why are they not spheres? • Most likely they are asteroids that were captured by the Martian gravity.

Explanation of Planetary differences • One major explanation of planetary differences is the role of size and density. • Small planets have cooler more solid cores. As a result, they have little tectonic activity. • In the broadest sense, is the moving of the crust, earthquakes, and volcanic eruptions.

What is a result of tectonic activity? • Tectonic activity causes the surface of a planet to change. Craters formed by asteroids are lost due to lava flows. Dramatically shaping the planets surface • If conditions are right, liquid water may form and surface features may change even further due to water erosion. • Gases are released from volcanic eruptions and form the atmosphere.

Planetary size and activity • atmosphere. – small and tectonically inactive, no – Small – dead • – slightly larger, evidence of an active past, but currently non active and a limited atmosphere. – Medium – once active • – largest of the terrestrial planets, Hot liquid cores that result in tectonic activity. Little to none of the original planetary crust is evident, constantly being reshaped by erosion and eruptions. – Large – active

Distance from the Sun • Distance from the Sun affects surface temperature. This in turn determines if matter will be a solid, liquid or a gas. • Can also affect the atmosphere • How high water molecules can be found • If it is so hot gases will be able to escape. Resulting in no atmosphere at all. (Mercury)

The role of water content • Water can be split into its parts by UV light. The heavier Oxygen sinks back into the atmosphere, and the lighter Hydrogen escapes into space. – Photo dissociation – breaking up of water molecules into H and O. • As a result H concentration drops. On Venus water vapor can be found high in the upper atmosphere where it encounters UV light. • On Earth because of a reduced greenhouse effect, water vapor freezes at about 30, 000 ft and then sinks. It does not encounter the UV light and therefore, H concentration on Earth is higher than Venus.

Earth has been shaped by biological processes • Plants have added O 2 to our atmosphere by breaking down water molecules during photosynthesis. • Humans and other organisms have shaped the planet surface by construction, destruction, and altering patterns of erosion.

Terrestrial Planet Test Review • • • Order of planetary size Difference between the planets General information about each planet (atm. , volcanoes, etc. ) Why Mercury has no atm. Why Mars has an atm. Role of distance from Sun on planetary characteristics Differences in planetary topography, and why Role of water content in the atm. Venus and its odd orbit, explain Venus and its atm. • • Mars and its hydrological story Greenhouse effects Role of planet size, tectonics and an atm. Atm. Formation UV light and water Info from Mars Rovers movies Rotation and magnatism

Are “manned” missions to Mars or outer planets necessary? • After reading the article address the question • Include in your answer supporting statements indicating why they should be manned or unmanned and the drawbacks of the opposing view. • Indicate problems that may be encountered and how you would address them. • Example: • I think that manned missions are need because of X, Y, and Z. , unmanned missions would limit us in these ways A, B, C. Manned missions would encounter the following problems: 1, 2, 3. I would address these problems in the following ways…