Astronomy Class Notes

Monday, April 13, 2009

- final May 4^th 3.30-6.30

- Goldilocks Theory

	Venus	Earth	Mars
Liquid H2O	Too hot (run-away greenhouse effect)	Just right	Too cold (used to have thicker atmosphere and warmer)
Distance in AU	0.7	1	1.5

o rain washes out CO2 but if you have a mechanism for putting CO2 back in like volcanism (outgassing) then CO2 is put back in and there is equilibrium but mars cooled so geologically inactive

- Modifications Necessary to the Goldilocks Hypothesis

o Supercomputer have shown that this hasn’t taken into effect that

§ The sun was once dimmer

§ The solar wind stripping the atmosphere

o Mars

§ Problem

· Now has 0.006 bar (one bar of pressure is what you feel standing on the earth)

· 3 billion years ago had to have 2-3 bars for water to exist in the liquid form

· The early sun was less bright so you need more carbon dioxide than what Mars currently contains in polar caps

§ Solution

· Carbon dioxide frozen clouds

· Perhaps a little bit of methane in the atmosphere

o Methane more common in outer solar system but no inconceivable that it was in the atmosphere of mars

· Solar wind

o Strip particles from the stmosphere of Mars, this is plausible but the question is why did mars ever have an atmosphere if solar wind was so powerful?

§ Core had enough molten metal and mars rotated rapidly enough that mars may have had a stronger magnet field before it cooled down and died geologically

· Ultraviolet Radiation (charged particles, protons and electrons)

o Without an ozone ultraviolet radiation comes in and hit the water and changes it into it’s constituents, Hydrogen leaves, Oxygen some leaves, some gets absorbed in the ground, another reason there doesn’t seem to be enough CO2 or H2O frozen in the ice caps

§ Note: We know that there was liquid water on mars because of the photographic evidence that there was fast moving liquid on the ground of Mars at one point, so these theories are used to explain this

· While these solutions are plausible it is open to change

o Venus

§ Solar dimming has raised the question that perhaps there might have been liquid water on venus at some point

· So close to the sun that it is hotter than the earth, so the amount of water vapor will be more in venus atmosphere than earth atmosphere, which repeats itself and becomes a run away greenhouse effect

· “Fate was sealed by distance”

§ Now almost no water in the atmosphere, get rid of the water by:

· Ultraviolet radiation

o Breaks up H2O

§ Hydrogen leaves

§ Some oxygen makes sulfuric acid

§ Remaining oxygen get kicks out by the solar wind

· Why is this scenario more believed than mars’s scenario?

o Isotopes

§ Hydrogen made up of 1 proton

§ Deuterium made up of 1 proton, 1 neutron

§ Tritium made up of 1 proton, 2 neutrons

§ For isotopes if you change the protons you change the elements so these are all isotopes of hydrogen

o Little water vapor that is left on venus is heavy water

§ Heavy water is when you replace 1 hydrogen atom with deuterium atom

§ When this is broken up by ultraviolet it is harder for it to leave because it is heavier

§ When you look at the atmosphere it supports this because there is presently more deuterium in the atmosphere than hydrogen

- Escape Velocity compered to thermal velocity

o Vesc = square root (2GM)/r

§ Can calculate the escape velocity of the earth

o Vthermal = square root (2kT)/m

§ This shows the most probable velocity of the particles in a given volume is going

§ Shows that hydrogen is going slower than the Vesc of earth and mars

· Can’t keep hydrogen however because of the high velocity tail (fast moving particles on the right side of the curve) leave

· Curve is then truncated on the right side, however the particles that remain continue to collide, these collisions repopulate the fast-moving tail, but since there are less particles the curve gets a little smaller

· Cannot hold hydrogen because they will continue to lose the tail until you loose about everything

Wednesday, April 15, 2009

Chapter 11

- Satellites

o 4 satellites that visited the gas giants 40 years ago because they were relativefly lined up

§ Pioneer X, XI

§ Voyager I, II

· Designed to sling shot from one planet to another and then out of the solar system

o Jupiter had the Galileo satellite visit it

o The cassini visited Saturn

- Rings of the gas giants

o All have this

o Jupiter least pronounced

o Not solid, little chunks of ice in orbit

o Not permanent phenomena, much debris will end up crashing onto the planet

- Moons

o Jupiter

§ Galilean satellites (all bigger than the moon)

· Discovered by Galileo

· 4 of the biggest in the solar system

· 2 inner moons are smaller and denser too outer are bigger and less dense (in minature of the solar system)

· Names after jupiter’s lovers

o Io

§ Yellow

§ Full of sulfur compounds

§ Most volcanic body in the solar system

§ Tidal forces from Jupiter flewes Io so it imparts mechanical energy, which flexs and heats the planet to the state where it is constantly heated to extreme temperature

§ Mostly sulfur molten materials

o Europa

§ 2^nd most likely body to host life in the solar system

§ Looks like the north pole

§ Thinks there is water under the ice sheet

§ Flewed by Jupiter but not to the extremes of Io

o Ganymede

§ Bigger than mercury

§ Icy but the ice layer is thicker

§ Has craters

o Callisto

§ Surface is less active than others

§ Lots of craters

§ “eroded” craters

· Icy crustal motion does this

o Saturn

§ Black separation in the rings is called the Cassinni division

§ 1 big satellite and a lot of little ones

· Look like rock

· Titan

o Larger than mercury

o Has an atmosphere

§ 60% thicker than earth’s atmosphere

§ Primarily nitrogen

§ Very cold

Friday, April 17, 2009

- Exam 4, 25 multiple choice, 5 quantitative

- Saturn

o Satellite titan

§ Atmosphere primarily of molecular nitrogen (like earth)

· However unlike the early earth is has a lot of hydrocarbons (methane, ethane)

§ Only gets 1% of the sunlight that the earth gets

· Brutally cold

§ Conditions on titan are such that ethane is close to it’s triple point, meaning that it is almost able to be solid, liquid, gas

· Note: on earth water is at it’s triple point

· People thought might rain ethane with “ethane lakes”

o Looking at photos can tell there are smooth non-reflecting areas, which could be liquid

- Uranus

o Light bluish tint, recognizable by its color

§ Reason is a lot of methane, which strongly absorbing in the red, see reflection which is leftover light which is blue

o Doesn’t have horizontal bands because it is orbiting on its side, tilted 98 degrees

o Rings

§ Discovered from an airplane

§ Observing Uranus in the infared while passing in front of a star, trying to time it to measure how thick uranus’s atmosphere but before Uranus got there the star “blinked” five times, it was the ring system

o Moons

§ Rocky, cratered

- Neptune

o Methane in the atmosphere

o Blue but shows more clouds (icy)

o Great dark spot on it but didn’t last very long, storm only lasted 30-40 years

o Rings

§ Not visible from earth

§ Found by spacecraft

o Moon

§ Triton

· A lot of ice

· Like gamymede and callisto

· Going around the planet backwards

o Means it had to be a captured moon

o If the moon goes backwards from the direction of rotation of the planet the tidal forces pull it in, eventually it will be destroyed by these tidal forces

§ Some debris will crash into Neptune

§ Some will go into the atmosphere

§ Some will go into the ring system

· Thin atmosphere