Unit 2 - Planets Flashcards
What are Kepler’s laws?
1) planets have elliptical orbits around suns
2) planets must travel faster when closer to the sun
3) r^3 is directly proportional to T^2
Define escape velocity
the minimum velocity required to escape a gravitational field
What is the relationship between escape velocity and a planet’s ability to retain its atmosphere?
hotter temperatures means gas molecules travel faster, if this is faster than the escape velocity the atmosphere will escape
What is the nebular theory?
the sun and planets all had a common origin - formed from a huge cloud of interstellar gas and dust
What does the nebular theory provide evidence for?
1) all planets lie one on plane
2) the sun rotates in the same direction and most moons orbit this same way
3) most planetary orbits are near circular
4) all planets orbit in one direction and rotate in this direction
What is accretion?
the formation of planetesimals
Explain accretion
collisions between small pieces of material results in some sticking together, snowball effect causes them to increase in size and mass, increased mass means increased gravitational forces
Describe the composition of terrestrial planets
consist largely of metals and silicates since they are close to sun and only heavier elements condense here
Describe the characteristics of terrestrial planets
small core, small volume and high density
Describe the composition of jovian planets
planetesimals formed from collisions of ice, core becomes massive enough to exert a strong enough gravitational pull to trap H and He to form a large gas atmosphere
Describe the characteristics of jovian planets
much larger than terrestrial planets since more ice available then metals/silicates, large volume, low density gaseous outer atmosphere and high density icy core
Describe the characteristics of Mercury
small radius, low mass, cratered surface due to meteorites and long folds in the surface thought to be wrinkles in the crust formed as it cooled and shrank, suggests Mercury hasn’t been active for a long time
What are the effects of Mercury low gravitational field strength?
1) low escape velocity so no atmosphere, heat escapes quickly
2) no moons
Describe the characteristics of Venus
similar size and mass to Earth, extremely hot surface temperature, high winds, high pressure, few craters on surface and many volcanoes
Why does Venus have such a high surface temperature?
extreme greenhouse effect - the high temperature due to being close to the sun meant gases in the atmosphere couldn’t condense to form oceans
Describe the composition of the Earth
core (inner and outer) made up of iron and nickel, thick mantle made of silicates and the thin crust
What are the 3 factors which protect life on Earth?
1) liquid water ocean
2) ozone layer
What are the 4 main stages of evolution of the Earth?
1) differentiation of layers
2) bombardment of the crust by meteorites
3) flooding of lava, then liquid oceans
4) surface evolution due to air, water and plate tectonics
What is unusual about the Moon and how is it thought to have formed?
it is Earth’s only natural satellite and has a large diameter (1/4 De) compared to moons of other planets
formed due to a collision on the young Earth
Describe the characteristics of Mars
reddish appearance due to iron oxide dust, thin atmosphere since small gravitational strength
What is apparent retrograde motion?
when the motion of a planet appears to reverse due to Earth’s orbit being inside that of the other planet and since Earth travels faster it ‘overtakes’ - happens every 2 years with Mars
What evidence is there for water and life on Mars?
water - hematite has been discovered on the surface and there is still water stored under the ice
life - studies of a meteorite from Mars shows fossilised carbonate globules
Why are Mars’ 2 moons irregularly shaped?
thought to be asteroids captured by the gravitational pull of Mars
due to small mass don’t have a large enough gravitational strength to squeeze them into spheres
Describe the composition of Jupiter
composed of mainly hydrogen and helium
intense magnetic field thought to arise from electrical currents in the rapidly spinning metallic hydrogen interior
Describe Jupiter’s rotation
differential rotation - rotates faster at equator than poles
rapid rotation has caused the planet to oblate (flattened perpendicular to spin)
What are the zones and belts on Jupiters?
zones - rising currents of gas
belts - falling currents of gas
Explain why Jupiter is hotter than it should be according to the laws of black body radiation
due to gravitational contraction under its own gravitational forces
atoms are accelerated to higher speeds resulting in increased temperature
Describe Jupiter’s moon Io
similar composition to terrestrial planets
cracked and distorted surface due to strong tidal forces produced by the planet’s gravitational pull causes volcanic
Describe Jupiter’s moon Europa
solid surface made of ice rather than silicates
tidal forces produced by Jupiter crack the surface and allow liquid to escape, this freezes and forms ice ridges
Describe the characteristics of Saturn
low density and shows differential rotation like Jupiter
Describe the composition of Saturn
made mostly of H and He with a dense core of metals like iron and nickle
What are Saturn’s rings made of and how are thought to have formed?
small chunks of rock and ice
remnants of a an old moon, fragments are then stretched out to form rings due to Kepler’s laws
Describe Saturn’s moon Titan
thick atmosphere with a similar pressure to Earth and similar physical features to Earth but methane instead of water
Describe Saturn’s moon Enceladus
extremely cold due to high reflectivity
close vicinity to Saturn means tidal forces crack the surface and water is forced through the cracks
Describe the composition and characteristics of Uranus
made of H, He and methane
ring structure similar to Saturn
blue-green appearance due to methane
What makes Uranus different to all the other planets?
spins parallel to its orbit plane
thought to be a result of a collision with a large object on the early solar system
Describe the composition and characteristics of Neptune
similar composition to Uranus
faint ring structure
What is unusual about Neptune’s largest moon Triton?
rotates about Neptune in the opposite direction to the planet’s rotation
thought to be a Pluto like object captured from the Kuiper Belt
Describe the composition and characteristics of Pluto
rocky and icy composition, more like a comet rather than a jovian planet
smooth surface suggests volcanic activity
demoted to a dwarf planet since hundreds of other similar bodies were discovered in the Kuiper Belt
How did the sun form?
centre of the interstellar cloud (mainly H) collapses and heats up until it becomes hot enough for nuclear fusion
outward thermal pressure balances inward gravitational forces
What is plasma?
a ‘soup’ of charged particles which conducts electricity since the nuclei and electrons are free to move
What are sunspots and how do they form?
dark areas on the surface of the sun due to reduced temperature
differential rotation causes plasma to become twisted and so too the magnetic field, when the field is tightly wound plasma loops form
What are coronal loops or prominances?
large loops of plasma looping in and out of the surface of the Sun
What are coronal mass ejections?
violent events which eject large amounts of material (plasma) into the outer solar atmosphere and beyond
What are the negative effects of a CME that erupts in the direction of the Earth?
damage to satellites, danger to astronauts and causes electrical interference / blackouts over large areas on Earth
What natural phenomenon is produced by solar wind?
aurora, the charged particles in the wind pass through the atmosphere and collide with O and N molecules, releasing light energy
What are exoplanets?
planets outwith our solar system orbiting other stars
What is the radial velocity method of detecting exoplanets?
monitoring the oscillating wavelength of light emitted by a star due to the Dopler Effect
useful for finding large planets with short orbital periods
What is the planetary transits method of detecting exoplanets?
observing the oscillating brightness of the light emitted by a star as a planet orbits around it
also allows the study of the planet’s atmosphere using spectroscopy
