Europa has 2 characteristic properties:
(i) Europa is a bright satellite with a highly reflective surface, and
(ii) Europa has virtually no impact craters visible on its surface.
(a) Give an explanation for each property.
(b) How are these two properties related?
(c) Approximately how old is Europa?
(2) Regular vs. Irregular
(a) Give 3 properties of a regular satellite:
(b) Provide an example of a regular satellite:
(c) Provide an example of an irregular satellite:
(d) What is inferred about the origin of a satellite from the regularity/irregularity of its orbit?
(e) Suppose we find a moon orbiting around a planet at a distance of 100,000 km, and a student says: "Perhaps this moon was originally an asteroid orbiting the Sun, and it just happened to drift close to the planet until it as only 100,000 km away from it, where it was caught by the planet's gravity, and it has been orbiting here ever since." Using the law of conservation of energy, explain why this scenario is physically impossible, and why a capture process must be more complicated than this. Please ignore the effect of the Sun's graity in your analysis. It is irrelevant.
(3) Atmosphere of Titan
(a) Describe the atmosphere of Titan.
(b) What do we know about the surface of Titan?
(c) Do a quick search around the web and answer: What are some of the most interesting things that the Cassini-Huygens mission has revealed about Titan?
(4) Making a Model of Planetary Rings
(a) The rings of Saturn are about 70,000 kilometers across but only 20meters thick. Suppose you wanted to build a model of Saturn's rings out of a sheet of plastic that is 2 mm thick. To keep the proportions right, how large a sheet of plastic would you need to make the scale model realistic? Show your work.
(b) To model Uranus' thin rings, strings of spaghetti (or perhaps, strictly speaking, linguini) would be more appropriate than sheets of plastic. Uranus' rings are also only about 20 meters thick and extend around the planet in a thin ring at a radius of about 50,000 km. If you wanted to build a model of Uranus' ring using 2mm thick pasta - how long a piece of spaghetti would you need? Show your work.
(5) Ring Particle Collisions
(a) Each little lump of ice in the densest part of Saturn's rings collides with another ring particle every 5 hours. If ring particles survived for the age of the solar system, how many collisions would it undergo?
(b) Given your answer in (a) above, explain why this means rings have been formed very recently.
(6) Distances and Velocities
(a) A space probe is 22 AU from the Earth. How much time will it take its radio signals to travel through space to reach us? Give your answer in hours.
(b) If it takes 20.5 hours for light from a Kuiper Belt Object to reach us, what is its distance? Give your answer in AU.
(c) A space probe is launched on a mission requiring it to travel a distance of 2.5 AU in 9 months. What must be this space probe's average speed? Give your answer in kilometers per second
Homework 12
Meteor life story
Briefly list the few major events in the history of an object that causes a typical shooting star (meteor) from the beginning of the solar system up to the point that you observe it.
(2) Armageddon
A group of protesters gather outside the White House, chanting and singing songs. On CNN one of them says, "Like whoa Mister President! Our mother Earth is in horrible danger from this nasty space meteor! It's over 109 nanometers in diameter and has a mass of over FIFTY THOUSAND GRAMS! This bogus thing is made of the same material as the Meteor Crater in Arizona, and it's totally gonna get within a thousandth of an AU to our sacred planet! If this destroys the Earth, that would have a majorly bad effect on the rain forest! Mister President, you gotta give us, like 150 billion dollars or so, and create like a new government agency to save us all! Anything else would be bad karma!
The President turns to you, his Science Advisor, and asks
(a) "How big is this object in everyday terms? " (Give an example of an everyday object that has this size. Give an example of an everyday object that has this mass.)
(b) "How close will it get?"
(c) "If this survived the atmosphere intact and hit the Earth, how big of a crater would it make"
(d) "Should we worry and/or do anything?" Explain.
(3) Heating up and cooling down.
(a) Describe 2 processes that heat up a planet
(b) Describe 2 processes that cool a planet.
(4) Rate of Impacts
Impact scars can be found all over the solar system. The Shoemaker-Levy-9 events showed that impacts can still occur. It is generally believed, however, that the rate of impacts dramatically slowed down about 3.8 billion years ago - about 700 million years after the formation of the solar system.
(a) What is the evidence for the change in rate of impacts?
(b) How do we know that the change in impact rate happened 3.8 billion years ago (rather than 3.2 or 4.1 billion years ago)?
(c) Give a possible reason why the impacts slowed down.
(5) Time scale for the solar system.
In this question we construct a scale model for the solar system, similar in principle to the scale models that can be found at most planetariums or science museums. Instead of scaling DISTANCE we are scaling TIME. The idea is to get a sense of relative times between important solar system events. We use Boulder as a sample location - but you could pick any where).
(a) Take your age (you may round it off to 20 years if you wish) to be scaled down to 1 second. What does this make our scale factor? That is, how many seconds are there in 20 years? This is the amount we will be speeding up time (or scaling down time scales).
(b) So, in our scale model for the solar system, you were born 1 second ago. Using the same scale factor, how long ago was the town of Boulder founded? Let's use 1860, the year when the Wellman brothers planted the first wheat crop in Boulder County, and the year when the first schoolhouse in Colorado built strictly for educational purposes was erected in Boulder on the southwest corner of 14th and Front [Walnut]. In our model, how many seconds ago were these events?
(c) If we guess that native americans were in Boulder about 10,000 years ago, how long ago is that in our scaled model? (For this and the following questions, please convert your answer to minutes, days, or years -- whichever is most appropriate. It's much more useful to say 8.3 minutes than 500 seconds!)
(d) The Flatiron Mountains were formed about 40 million years ago. Use the scale factor to find how long ago that is in our scale model for time scales of the solar system.
(e) Dinosaurs hung around Boulder about 120 million years ago - what's this scale to?
(f) Fossils tell us that life first existed on land about 400 milion years ago - those are the fish that flopped about and learned to breath air - put that date on scale model.
(g) The earliest life is thought to have appeared on Earth about the time of the end of the period of heavy bombardment of the planets (when the cratering slowed down). This makes sense, doesn't it, that the slime and creepy-crawlies would have a hard time surviving until the aerial bombing ceased - that was about 3.8 BILLION years ago. What does that scale to?
(h) Calculate the scaled time for the formation of the Earth,4.6 billion years ago.
(i) Finally, calculate the scaled time for the big bang, the formation of our universe 13.7 billion years ago
(6) Orbits, Shepherding, and Resonance
(a) In the context of planetary rings, explain how shepherding works. Why do you need two moons on either side of a ring in order to hold it in place?
(b) How did orbital resonance lead to the formation of the Kirkwood gaps in the asteroid belt?
(c) Suppose that we have a small ice particle that orbits Saturn every 5 hours, and suppose that there is a moon out farther from Saturn that orbits once every 15 hours. How will that moon affect this ice particle? What will be the end result of this relationship?
(7) The Logic of Science: Theories and Observations
Below we have listed a series of 12 scientific ideas. Six of these are theories and six are patterns of observations. For every one of these six theories, we have listed a pattern of observations that supports it. For every one of these six patterns of observations, we have listed a theory to explain it. For each one you must do two things: 1. Identify it as theory or observation. 2. Write down the number of its pair.
In atoms, electrons are only allowed in certain orbits (which correspond to energy levels), and photons of light are produced when electrons move between these orbits.
There are many craters on the Moon and Mercury, fewer on Mars, and not very many on the Earth and Venus.
When heated until it glows, a gas of each element produces a unique pattern of spectral lines.
All the objects in our Solar System formed out of one disk of material that orbited our Sun as it formed 4.6 billion years ago.
There is a force called gravity, which attracts every object in the universe to every other object, and this force gets weaker with distance.
Near the Sun, only rocks and metals are in solid form, while far from the Sun, the ice materials become solid too. As a result, when the Solar
System formed, planets far from the Sun could grow much larger.
All the planets in our Solar System orbit the Sun going in the same direction, in a flat disk. Most planets also rotate in this direction, and most moons do too.
Inside very large Jovian planets, there is enough pressure to turn hydrogen into a liquid form that conducts electricity.
All terrestrial planets formed with molten interiors, but smaller planets cooled more quickly, causing their volcanoes to go dormant. The interiors of larger terrestrial planets cooled more slowly, so their volcanoes could remain active for a much longer period of time.
The planet Jupiter has an extremely powerful magnetic field.
Terrestrial planets are found nearest the Sun, while Jovian planets are found farther away.
All orbits of moons around planets, planets around stars, and stars around each other are in the shape of ellipses.