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Astronomy 1021 Study Guide - Midterm Guide: Kuiper Belt, Giant Planet, Semi-Major And Semi-Minor Axes

Course Code
ASTR 1021
Sarah Gallagher
Study Guide

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Astronomy Term Test Notes
Chapter 6: Solar System — Big Picture and Origin
-What processes shape planetary surfaces?
-gravitational potential energy is converted to kinetic energy, which upon impact is converted to
thermal energy
-light materials rise to the surface while heavy materials fall to the core, converting gravitational
energy to thermal energy
convection (cooling process)
-transports heat, cool material falls, hot material rises
conduction (cooling process)
-transfers heat from hot material to cool material
-sends light energy into space
-terrestrial planets form closer to the sun where the temperatures are suitable for rocks and metals for
form and fuse together
-jovian planets form farther from the sun, where the temperatures are low enough for ice
ice, rock accretion — making bigger planets
-THE NEBULAR THEORY: states that the solar system was formed in a gravitational collapse of the
interstellar cloud of gas and dust
as the solar nebula shrank in size, three important processes altered its destiny
-heating — increased as it collapsed, as the cloud shrank, its gravitational potential energy was
converted to the kinetic energy of individual gas particles falling inward
-spinning — the solar nebula rotated faster and faster as it shrank, represents conservation of
angular momentum of a rotating cloud
-flattening — the solar nebula flattened into a disk, a natural consequence of collisions between
particles in a spinning cloud
dating rocks
-radiometric dating, relying on careful measurement of the proportions of various atoms and
isotopes in the rock
-age dating the oldest meteorites shows the solar system to be 4.5 billion years old
Chapter 7: Terrestrial Planets
Phobos, Deimos
cold desert, giant volcanoes, huge canyons, polar caps, water used to flow in a distant past
-we know there was once water because there are dry riverbeds that are signs of erosion
-victim of planetary freeze drying — polar caps that contain frozen carbon dioxide

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1.5 AU from Earth, days are one hour longer than days on Earth
Similar seasons to Earth, due to its axis
volcanic valleys, Valles Mariheris
semi-major axis of 1.524 AU
mass = 6.39 × 1023"kg
surface as liquid water, stable atmosphere, climate stability, atmospheric oxygen
global warming is happening due to human activity increasing and the global temperatures are as
-this can drastically change climate patterns
has the strongest magnetic field
semi-major axis of 1 AU
mass = 5.972 × 1024"kg
No moons
5% smaller than Earth in radius
hot, covered in volcanoes
-thick, carbon dioxide atmosphere (this is why it is so hot)
has many impact craters, evidence of tectonic forces, though it does not have tectonic plates like
Earth does
-Venus either has a weaker mantle convection process or a lithosphere that resists fracturing,
possibly because of its heat
geological features include: impact craters, volcanoes, evidence of surface tectonics, almost
certainly geologically active
semi-major axis of 0.72 AU
mass = 4.867 × 1024"kg
No moons
geologically dead
looks almost identical to the Moon, impact craters all across it, indicating its old age
-craters are less crowded, possibly suggesting that molten lava covered these carters
-Mercury seems to have shrunk, leaving behind large cliffs
semi major axis of 0.3871 AU
mass = 3.285 × 1023"kg
The terrestrial planets formed close to the Sun where temperatures were well suited for rock and metal
to condense. After the heavier elements and minerals condensed into solid bits of rock, they all orbited
the sun at the same speed, and when they collided, they stuck together instead of destroying one
another. These pieces gradually grow larger due to a process called accretion, and eventually, when
they were large enough, gravitational pull formed them into spheres.

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The greenhouse effect is the process by which radiation from a planet's atmosphere warms
the planet's surface to a temperature above what it would be in the absence of its atmosphere. If a
planet's atmosphere contains radiatively active gases (i.e. greenhouse gases) the atmosphere
radiates energy in all directions. Without the greenhouse effect, the Earth’s temperature would be well
below freezing.
ATMOSPHERE: Supplies the oxygen that we breathe, protects us from solar radiation and makes our
planet warm enough for liquid water to exist: something that is very obviously crucial to our existence.
Earth’s atmosphere is a mix of gases: 77% nitrogen, 21% oxygen, with trace amounts of argon, water,
vapour, carbon dioxide, and other gases.
VOLCANISM occurs when underground molten rock finds a path to the surface, causing eruptions.
TECTONICS are forces acting on lithosphere, causing earthquakes
EROSION is the breakdown of material through the elements (rain, snow, water, wind, etc.)
Used to calculate half lives, A half-life is NOT one-half the age of the rock! When the material is
liquid or gaseous, the parent and daughter isotopes can escape, but when the material solidifies, they
cannot so the ratio of parent to daughter isotopes is frozen in. The parent isotope can only decay,
increasing the amount of daughter isotopes. Radioactive dating gives the solidification age. When the
rock melts, the radioactive dating "clock" gets reset.
There are two simple steps for radioactive dating:
1 Find out how many times you need to multiply (1/2) by itself to get the observed fraction of
remaining parent material. Let the number of the times be n. For example 1/8 = (1/2) × (1/2) ×
(1/2), so n = 3. The number n is the number of half-lives the sample has been decaying. If
some material has been decaying long enough so that only 1/4 of the radioactive material is left,
the sample is 2 half-lives old: 1/4 = (1/2) × (1/2), n =2.
2 The age of the sample in years = n × (one half-life in years).
-processes that shape the terrestrial planets’ surfaces
IMPACT CRATERING — the creation of bowl-shaped craters made by asteroids of comets striking
a planet’s surface
VOLCANISM — the eruption of molten rock from a planet’s interior to its surface
TECTONICS — the disruption of a planet’s surface by internal stress
EROSION — weathering, wearing down or building up of geological features by wind, water, ice,
and other phenomena of planetary weather
without life, Earth would lack atmospheric oxygen and a ozone layer
the ozone hole has a minor cooling effect (2% of the warming effect of greenhouse gases)
Chapter 8: Jovian Planets
Io, Europa, Ganymede, Callisto
Io is the wolcano world
Europa could be the water world, currently covered in ice
Ganymede and Callisto show intriguing geology, both having surfaces of water ice
-Ganymede has large and densely cratered areas, others are light and barely cratered
-Callisto is a heavily cratered ice ball
-5.20AU from Sun
-318M of Earth
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