Astronomy

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Previous Lessons
Open Chapter Ch. 1: A Modern View of the Universe
Lesson #1 The Scale of the Universe
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Lesson #2 The History of the Universe
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Lesson #3 Spaceship Earth
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Open Chapter Ch. 2: Discovering the Universe for Yourself
Lesson #4 Patterns in the Night Sky
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Lesson #5 The Reason for Seasons
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Lesson #6 The Moon, our Constant Companion
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Lesson #7 Ancient Mystery of the Planets
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Open Chapter Ch. 3: The Science of Astronomy
Lesson #8 The Ancient Roots of Science
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Lesson #9 Ancient Greek Science
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Lesson #10 The Copernican Revolution
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Lesson #11 The Nature of Science
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Open Chapter Ch. 4: Understanding Motion, Energy, and Gravity
Lesson #12 Describing Motion
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Lesson #13 Newton's Laws of Motion
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Lesson #14 Conservation Laws in Astronomy
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Lesson #15 The Force of Gravity
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Open Chapter Ch. 5: Light: The Cosmic Messenger
Lesson #16 Basic Properties of Light and Matter
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Lesson #17 Learning from Light
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Lesson #18 Collecting Light with Telescopes
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Exam Exam 1
Open Chapter Ch. 6: Formation of the Solar System
Lesson #19 A Brief Tour of the Solar System
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Lesson #20 The Nebular Theory of Solar System Formation
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Lesson #21 Explaining the Major Features of the Solar System
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Lesson #22 The Age of the Solar System
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Open Chapter Ch. 7: Earth and the Terrestrial Worlds
Lesson #23 Earth as a Planet
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Lesson #24 The Moon and Mercury: Geologically Dead
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Lesson #25 Mars, a Victim of Planetary Freeze Drying
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Lesson #26 Venus, a Hothouse World
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Lesson #27 Earth as a living planet
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Open Chapter Ch. 8: Jovian Planet Systems
Lesson #28 A Different Kind of Planet
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Lesson #29 A Wealth of Worlds: Satellites of Ice and Rock
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Open Chapter Ch. 9: Asteroids, Comets, and Dwarf Planets
Lesson #30 Classifying Small Bodies
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Lesson #31 Asteroids
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Lesson #32 Comets
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Lesson #33 Pluto and the Kuiper Belt
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Lesson #34 Cosmic Collisions - Small Bodies vs Planets
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Open Chapter Ch. 10: Other Planetary Systems
Lesson #35 Detecting Planets Around Other Stars
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Lesson #36 The Nature of Planets Around Other Stars
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Lesson #37 The Formation of Other Planetary Systems
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Exam Midterm Exam
Open Chapter Ch. 11: Our Star
Lesson #38 The Sun, Our Star
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Lesson #39 Nuclear Fusion in the Sun
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Lesson #40 Sun-Earth Connection
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Open Chapter Ch. 12: Surveying the Stars
Lesson #41 Properties of Stars
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Lesson #42 Patterns in the Stars
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Lesson #43 Star Clusters
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Open Chapter Ch. 13: Star Stuff
Lesson #44 Star Birth
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Lesson #45 Life as a Low Mass Star
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Lesson #46 Life as a High Mass Star
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Open Chapter Ch. 14: The Bizarre Stellar Graveyard
Lesson #47 White Dwarfs
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Lesson #48 Neutron Stars
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Lesson #49 Black Holes: Gravity’s Ultimate Victory
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Exam Exam 3
Open Chapter Ch. 15: Our Galaxy
Lesson #50 The Milky Way Revealed
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Lesson #51 Galactic Recycling
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Lesson #52 The History of the Milky Way
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Open Chapter Ch. 16: A Universe of Galaxies
Lesson #53 Islands of Stars
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Lesson #54 Distances of Galaxies
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Lesson #55 Galaxy Evolution
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Lesson #56 The Role of Supermassive Black Holes
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Open Chapter Ch. 17: The Birth of the Universe
Lesson #57 The Big Bang Theory
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Lesson #58 Evidence for the Big Bang
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Lesson #59 The Big Bang and Inflation
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Open Chapter Ch. 18: Dark Matter, Dark Energy, and the Fate of the Universe
Lesson #60 Unseen Influences in the Cosmos
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Lesson #61 Structure Formation
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Open Chapter Ch. 19: Life in the Universe
Lesson #62 Life on Earth
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Lesson #63 Life in the Solar System
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Lesson #64 The Search for Extraterrestrial Intelligence
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Lesson #65 Interstellar Travel and Implications for Civilizations
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Exam Final Exam

Assignments:

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Lesson Objectives:

- Comparing Earth and Mars
- Geological activity
- Water
- Atmosphere



Mars has long been used in science fiction stories due to some similarities it shares with Earth.

For example, its surface looks like some of our deserts and volcanic plains. A Martian day is almost the same length as an Earth day - a little over 24 and a half hours.

It has polar caps with water ice. It also has a similar axis tilt, resulting in Earth-like seasons.

All of this and more has given rise to the idea that life on Mars would be possible. However, the Martian atmosphere is so thin that its atmospheric pressure is less than 1% of the pressure on the surface of the Earth. Such a thin atmosphere means a very weak greenhouse effect to keep in heat. As a result, the surface temperature is quite cold at -50 degrees Celsius. The Martian atmosphere also lacks oxygen and therefore has no ozone layer to block harmful ultraviolet radiation from the Sun.

However, evidence shows that Mars was warmer and wetter in the past, so there may have once been conditions more suitable for life.



Looking at Mars, the southern hemisphere is mostly higher-elevation terrain with many large impact craters, including the large crater known as the Hellas Basin.

In contrast, the northern hemisphere is made up of relatively smooth plains which tend to be below the average surface level.

This means the southern highlands are much older than the northern plains since the craters in the north were mostly erased by geological activity.

As we have learned previously, size is the most important factor in determining whether a planet will retain the internal heat necessary for geological activity. Mars is larger than the Moon and Mercury, so it has had more geological activity than both of them.

More specifically, Mars once had volcanic activity. There are many volcanoes on the surface including Olympus Mons which is the tallest peak in the solar system (26 kilometers high).

There is also evidence of tectonic activity in the past, such as the long, deep valleys called the Valles Marineris. These valleys are as long as the United States is wide and are four times as deep as the Grand Canyon.

As for the present, Mars is not geologically dead - it probably still retains some internal heat. There has been no evidence of recent volcanic or tectonic activity but one of its volcanoes could still erupt someday if its lithosphere has not thickened too much from the gradual cooling of its core.



There is no liquid water on the surface of Mars. It is too cold and the atmospheric pressure is too low, so any liquid water would immediately either freeze or boil away.

However, orbital and surface studies show evidence of flowing water in the past.

Photos have revealed dry riverbeds, most likely carved by running water. Based on studies of the impact craters in and near the riverbed, the water probably flowed through them around 2 to 3 billion years ago.

Many orbital images show evidence of ancient rainfall, with eroded crater rims, and river delta deposits.

Robotic rovers that landed in 2004 and 2012 found mineral evidence of past liquid water, with chemical analysis of one region suggesting a lake of relatively pure, drinkable, water.

Although there is no liquid water on Mars today, there are still significant amounts of water ice at the polar caps. Scientists estimate that if that ice were melted, it would cover the entire planet in a ten meter-deep ocean.



Many scientists believe that billions of years ago, Mars had a dense atmosphere from volcanic outgassing providing water vapor and carbon dioxide. This atmosphere would have created a stronger greenhouse effect than it has today, resulting in warmer surface temperatures.

It is still a mystery how it lost that atmosphere but the most likely problem was the planet's relatively small size. Early in its history, Mars' core was hot enough for volcanic activity and outgassing to provide the gases needed for an atmosphere. The heat in the core was also probably enough to create convection currents resulting in a magnetic field similar to what we have on Earth.

But as the interior cooled, volcanic outgassing stopped, and the magnetic field became weaker and disappeared altogether. Without this magnetic field providing a protective barrier against solar winds, its atmospheric gases were stripped away, the greenhouse effect diminished, and the surface froze.

In other words, if Mars were as large as Earth, maybe it would still have a moderate climate today.