Astronomy Test 1

Seasons:Caused by the tilt of Earth's spin axis.Why?In the summer, the days are longer, allowing more time for the Sun to provide heat.The sunlight is more direct and so heats better.There is less atmosphere in the way.
The Earth and the Moon:Surface age and planet age are not necessarily the same.Cratering gives an indication of surface age, using the Moon (maria and uplands) and Earth as a baseline. Assumes all bodies had the same cratering history, and that only surface processes could erase them.Erosion: surface processes that can resurface or erase craters.Surface dating: based on radioactive dating from rocks/core samples of the Earth and Moon. All other surface dating comes from cratering.Structure and composition of the Earth- and how this means the Earth was once molten.Factors that determine an atmosphere:Escape velocity (mass) of the object,the mass of the gas particles,temperature.
The other Terrestrial planets:Mercury: Know the structure and (roughly) density. Be able to determine surface age based on cratering.
Mercury is tidally locked to the Sun in a 3:2 spin:orbit resonance.
Has an extremely thin, evaporative atmosphere.Venus: Thick 95% CO₂ atmosphere.
Structurally like the Earth.
Lots of volcanoes.
Tectonic activity- resurfaced itself all at once about 500-800 million years ago.
Spins retrograde (backwards)
Greenhouse gasses make it the hottest planet in our solar system.Mars: Structurally like the Earth.
Thin 95% CO₂ atmosphere.
Younger, lower altitude northern hemisphere, which may have once contained an ocean (or at least lakes).
There is still water on Mars, in underground aquifers.
Mars has seasons (like the Earth) and spins at about the same rate (and with about the same tilt) as the Earth.Terrestrial Planets:Common Properties:Solid surfaces with thin atmospheres.Structure: Thin brittle crust, mantle, and core.Few moons (3 moons for 4 planets)Density roughly 5 g/cc.The 4 planets closest to the Sun
What determines what gasses and how thick an atmosphere is?Mass of the gas (more massive particles move slower).Temperature (hotter gas moves after).Mass of the parent object (planet, moon, asteroid), which determines the escape velocity.

Be sure you can identify features (list what you see and describe what it means).

And Know the scientific method

1. Make an observation (or do an experiment)

2. Create a theory (explanation) for the observation

3. Make predictions based on the theory (different from the original observation)

4. Test the predictions (do observations of what you predicted)

5. Confirm/modify/refute the theory.

Jupiter.

• Made mostly of H and He.

• Over 300 times more massive than Earth.

• Density is 1.3 g/cc.

• It is mostly a gas.

• Structure:

  • Cloudy atmosphere turning into a liquid.

  • Middle is mostly liquid metallic H.

  • Core of rock (5-30 times the mass of Earth).

Jupiter's Moons:

• Jupiter has over 60 moons- most are captured asteroids.

• The Galilean moons are all big, round, and likely formed with Jupiter.

• Io: The most volcanically active body in the solar system.

  • Density of 3.5 g/cc: made completely of rock.

  • Structure is like the inner solar system: crust, mantle and core all made of rock.

  • Extremely thin atmosphere made from volcanic outgassing.

  • No observable craters. Surfage age is younger than a few million years.

• Europa: Structure: Icy crust, liquid water ocean, then rocky mantle and core.

  • Density is 3.0 g/cc: mostly rock, but some water.

  • A few visible craters, but still a young surface (tens to 100-200 million years old).

  • Very thin oxygen atmosphere from particles hitting the icy surface.

  • Surface temperature is 130 K (-225^oF).

• Ganymede: The largest moon in the solar system (bigger than Mercury and Pluto).

  • Structure is icy crust, liquid water ocean, rocky mantle and core (like Europa, but more water).

  • Density is 1.9 g/cc showing it is about 50% water/ice and 50% rock.

  • White spots are craters (showing fresh ice). The surface is a bit over a billion years old (based on cratering).

• Callisto: Structure is icy crust, liquid water ocean (thin, perhaps slushy only), then the inner part is rocky/icy mantle-like material. It is unknown if Callisto has a differentiated core.

  • Density is 1.8 g/cc, like Ganymede.

• Of the Galilean moons, as you get farther from Jupiter, they become older and colder: Io is all volcanoes; Europa must have some under the water to keep the water from freezing; Ganymede has no obvious heat source, but still has liquid water; and Callisto may not even be differentiated with a surface that's several billion years old.

Saturn's interesting moons:

• Titan- the other Earth!

  • Has nitrogen atmosphere

  • At its temperature; water-ice crust (like our rocky crust) and methane/liquid which can be gas, liquid, or solid (like water for us).

  • Young surface shows mountain ranges (plate tectonics), cryovolcanoes, sand dunes (made of water-ice particles), rivers/lakes/streams of liquid methane.

• Enceladus

  • The whitest object known in our solar system.

  • Partially old surface, partially young surface

  • Young surface has creaks with water geysers.

  • Pockets of liquid water oceans beneath frozen ice crust.

• Structure of large bodies in our solar system:

• Terrestrial Planets (and our Moon and Io)

  • (Comparatively) Thin atmosphere

  • Rocky crust

  • Rocky mantle

  • Rocky core (maybe a liquid portion)

  • Density near 5 g/cc.

• Jovian (Jupiter and Saturn)

  • Mostly H (and then He) Gas and cloud exterior

  • Liquid H interior

  • Metallic H inside of that

  • Rocky (solid or molten?) core

  • Density near 1.0 g/cc

• Icy moons (if warm enough to differentiate)

  • Solid (water)ice crust

  • Liquid (water) ocean beneath that

  • Rocky mantle

  • Rocky core.

  • Density near 2.0 g/cc

  Neptunian (Neptune and Uranus)

  • Mostly H (and then He) atmosphere

  • Liquid/solid water/ammonia/methane mantle

  • Rocky core.

  • Density near 1.0 g/cc (really 1.4 g/cc)

Making our solar system:

• Giant gas cloud begins to shrink

• As it shrinks, it heats up (more towards the middle) and flattens into a disk.

• As it cools, rock-like material condenses first into smoke/dust-sized particles

• The dust sticks together into snowflake/dust bunny-like particles

• The larger conglomerates collide to build up pebbles, then boulders.

• The boulders collide to form planetesimals (pre-planets which are moon-sized).

• Inner solar system:

  • too hot for ices. Planetesimals collide into planets.

  • End up with terrestrial planets

• Outer solar system:

  • Cool enough for ice to form. Ice sticks to planetesimals, making the cores massive.

  • Massive cores can collect H/He gas, which is the most abundant materials. Making them gas giant planets.

• Star 'turns on' blowing away any remaining gas back into the galaxy.

Be sure you can identify features of planets.

And as always- Know the scientific method