Lecture 5: Planets in the Solar System, Lecture notes of Astronomy

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PLANETS

L E C T U R E 5

I. TWO TYPES OF PLANETS:

T E R R E S T R I A L S

Earth, Mercury, Venus and Mars. Earth is the largest, followed by Venus, Mars and Mercury being the smallest. Closer together in the solar system. Have solid surfaces (rocks and metals. Little to no Moon. Contain iron cores. No rings. Smaller in size and smaller mass. Denser than other planets. Closer to the Sun. Much warmer. No thick atmosphere. Closer to the Sun. Found in the inner part of the solar system. Has diverse features on the surface (craters, mountains, valleys, oceans, etc).

G A S G I A N T S :

Before planets form, these elements collides and clump together, eventually forming a cloud of gas and dust that is made mostly of hydrogen. Found outside the “Frost Line” of the solar system. The big giants, large atmospheres composed of hydrogen and helium. No solid surfaces. Have thick atmosphere. Has many/dozens of Moons. Rotates very quickly on their axes than terrestrial planets. Gas Giants are Jupiter and Saturn. Ice Giants are Uranus and Neptune since they're more water, ammonia and methane (ice) in their composition.

II. EARTH: Earth is the 3rd planet closest to the Sun in our solar system. The only known planet that supports life. Approximately 71% of Earth is covered by oceans with the remaining 29% being continents/islands. Orbits the Sun every 365.25 days and rotates on it’s axis every 24 hours. Oxygen did not originally come from the atmosphere, it was first created via Photoautotrophs. => Photoautotrophs are early organisms that secretes oxygen through photosynthesis. Hydrogen, helium, oxygen, H2O and nitrogen are evidence from 3.7 billion years ago. Multicellular organisms were the earliest evidence of ;life on Earth. => Single-celled organisms first appeared 3.5 billion years ago. => Multicellular organisms(sponges and algae looking organisms) first appeared around 600-800 million years ago. A giant layer that helps protect Earth. Created by generating electric currents produced by the movement of molten iron and nickel in Earth’s outer core. As the magnetic poles shift faster and faster, the magnetic field of Earth gets weaker. Rules: => Moving charges creates a magnetic field. => Magnetic field exert a force on moving charge (Sun sends in “solar wind” which are fast moving charge, mostly electrons to Earth. With Earth’s magnetic field, it protects the planet from those electrons). The atmosphere is Earth’s 2nd protector from solar wind.

M A G N E T I C F I E L D :

L A Y E R S O F E A R T H ’ S

A T M O S P H E R E :

TROPOSPHERE

STRATOSPHERE

MESOPHERE

THERMOSPHERE

EXOSPHERE

Lowest, thin layer; 11km; where weather can be seen. Contains the ozone layer (absorbs ultraviolet from the Sun); 50km. Meteorites burn upon entering since it is the coldest layer; 80km. Hottest layer; 160km. Outermost layer and extending out into space; atmosphere is very thin. II. EARTH: Without plate tectonics, Earth will be dominated by oceans. They form mountains and create volcanoes. Pangaea: historically a supercontinent that split apart due to the movement of tectonic plates which formed continents.. => Found in the middle of Atlantic ocean during the Cold War. => Provides evidence that plates are moving apart. America and Europe are moving apart approximately 3cm per year.

P L A T E T E C T O N I C :

V. VENUS Similar size, mass and density with Earth. Rotates in the opposite direction, 180 degrees axial tilt. Often referred to as Earth’s twin sister since both have similar size and composition. 2nd planet closest to the Sun. Orbital period is 225 Earth days. Sidereal day: 243 days. Solar day: 17.7 days. Has rocky surface covered with volcanic plains, mountains and large volcanoes. Surface is completely covered by thick clouds. Clouds are made of sulfuric acid. Approximately 95% of its atmosphere is made of CO2. Atmospheric pressure on Venus is 92x that of Earth’s. Thus, probes that landed does not survive. Has no Moons or rings. Known as the hottest planet in the solar system (temperatures can go up to ~460 degrees Celsius on the surface; lead will melt). => Reason: Thick atmosphere made of carbon dioxide with clouds of sulfuric acid traps the heat and causing extreme high temperatures on the surface.

4th planet from the Sun. Smaller than earth, about half its diameter. Often called the Red Planet due to its reddish surface (from iron oxide on its surface). Has a rocky surface with the largest volcano in the solar system, Olympus Mons (3x as tall as Mt. Everest and same size as the Arizona state). Orbits the Sun about 2 Earth years. Rotation period is 24 hours and 40 minutes. 25 degrees axial tilt. Seasons are similar on Earth but twice as long. Has a thin atmosphere made mostly of CO2 with some traces of nitrogen and argon. Around 95% CO2. Much colder than Earth and with no atmospheric protection from the Sun, temperature tends to vary widely during the day. Had evidence of water in the form of ice in the past. No magnetic field but in the past, it had a local magnetic field where some parts of the planet had said field. Craters on Mars suggests it was volcanically active in the past. Has two small irregularly shaped Moons, Phobos and Deimos. The thin atmosphere makes it difficult for water to exist in liquid state => water will boil and evaporate on Mars. => If a person without a protective suit go on Mars, water in the body will evaporate because there is no atmospheric pressure. VI. MARS