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L12. Outer Moons I
Astro 159 lecture 12 on the outer moons
29
Astronomy
Undergraduate 2
05/10/2011

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Term
Outside the snow line, what are planets and their satalittes made out of?
Definition
ICE and rock
Term
What are the three types of "dead" satellites?
Definition
Rings - close to the planet
Regular satellites
Irregular satellites - far from the planet
Term
Irregular satellites
Definition
Small
Formed by capturing asteroids
Prograde and retrograde orbits (they rotate the usual direction and the wrong direction).
Potato shaped
High eccentricity
High inclination
Far from the planet.
Term
Capture
Definition
When the gravitational pull of a planets catches a passing asteroid and turns it into their satellite (moon)
Term
Satallite
Definition
An object or objects that orbit around a planet like our moon.
Term
Regular satallites
Definition
Large- size of our moon
Form by co-accretion
Low eccentricity (circular)
Low inclination (orbits in the plane of the equator)
Close to the planet
Synchronous rotation
Made of ice and rock
Term
Eccentricity
Definition
How circular the orbit is
High= very elliptical (oval)
Low= circular
Term
Inclination
Definition
The incline or angle that the satellite orbits the planet on.
High= does not orbit on the equatorial plane of the planet.
Low= orbits around the equator of the planet
Term
Rings
Definition
All giant planets have them
The particles that make them are VERY small
Very low eccentricity
Very low inclination
Very close to the planet
Term
Gravity equation
Definition
F=(Mm)/d2
The gravitational pull between two objects of masses M and m
Term
Tidal Force
Definition
When small objects are close to large planet sized objects they are attracted to the planet.
The closer the object is to the planet the stronger the attraction
Term
**Roche Limit**
Definition
An area that extends 2.5 times the radius of the planet
Term
Inside the Roche limit
Definition
tidal forces win and objects are attracted to the planet,
they cannot accrete into larger objects and
They form rigngs
Term
Outside the Roche Limit
Definition
The tidal forces are not strong.
Objects are attracted to each other and not the planet.
Objects accrete and form satellites.
Term
Where do rings form and why?
Definition
Rings form inside the Roche limit because Tidal forces are stronger then the forces between objects and they cannot accrete together to form larger satellites.
Term
Where do regular satellites form?
Definition
Outlaid the Roche limit Where objects can accete (come) together.
Term
Dead satellites.
Definition
Satellites that have never been geologically active
Callisto, Mimas, Rhea, Iapetus, Oberon and Umbriel
They are often crater saturated.
Term
Satern's rings.
Definition
Made of ice
10-100m thick
Full of gaps.
Term
Why do saturn's rings have gaps.
Definition
When the material in saterns rings gets into resonance with saturn's moons (other satellites) the gravitational push of the moons kicks the material out of orbit with Saturn leaving a gap.
Term
Do Neptune and Uranus have rings?
Definition
Yes, they are much like saturn's
Term
Does jupiter have a ring?
Definition
Yes but it is extremely small
It is more spread out
It is made outlook of dark material from the grinding of up of nearby satellites.
Term
Why doesn't Jupiter have a big icy ring like the rest of the large icy planets?
Definition
Jupiter is so large that it has it's own snow limit.
Inside the snow limit ice is water.
It turns out, jupiter's snow limit is outside it's roche limit so ice cannot exist inside the Roche limit so Jupiter cannot have an ice ring.
Term
Crater saturation
Definition
A surface is so crowded in craters that new impacts just cover old ones.
You can no longer tell the Change in age of a surface.
Term
**Why can we not use crater counting to find the ages of objects in the outer solar system?***
Definition
Objects in the outer solar system have VERY different crater POPULATIONS (they have been hit by very different objects) then the inner solar system so we cannot compare their crater densities to the moon.
The only reason that we can use crater counting and crater density plots in the inner solar system is that All of the objects have similar R-Plots (crater populations) so we know they have all been hit by similar objects in the past.
Term
How can we find the age of surfaces in the outer solar system?
Definition
We must bring back a sample.
Term
How do we compare surfaces in the outer solar system?
Definition
We look at the spectrum that is reflected off of the surface to see what they are made of.
It is usually water ice in the outer solar system
Term
Water ice
Definition
Ice made out of water as opposed to ice made out of methane, ammonia, nitrogen or CO2
Term
Mimas, Rhea, Oberon and Ubriel
Definition
Dead worlds whose only facts we need to know are they you cannot use crater counting to find their ages because their crater populations (their R-Pots) are different then the moon.
They are made out of ice
And Mimas is barely big enough to be a sphere.
Term
Iapetus
Definition
A dead satellite
It is made of ice but it has a very low albido side because it travels through a cloud of blown off carbon and only one side gets hit.
It also has a weird mountain rage around it's equator that may have formed by the satellite spinning very fast.
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