Physics 9 The Solar System with Prof. D. Tytler Oct. 2000

Homework 4, due Nov 2 in class

We encourage you to work together, to discuss the topics and solutions, but your answers must use all of your own words, calculations and diagrams.

You must not hand in work copied from someone else.

Please write down the code numbers of all in your study group.

These problems all require thought.

  1. Sketch the orbit of an Oort cloud comet coming into the inner solar system for the first time.
  2. Give two reasons why this comet might not return to the Oort cloud.
  3. Imagine that an Oort cloud comet was first detected when it was crossing Jupiter’s orbit. Assuming that its speed is the same as Jupiter’s, how long would it take to reach the Earth’s orbit, if it were travelling directly towards the sun? Show the steps towards the answer.
  4. Will the comet’s speed vary along its orbit? If yes, give the reason(s).
  5. Estimate the probability that this comet will hit the Earth. Get an answer accurate to the nearest order of magnitude (e.g. 10-1, 10-2 , 10-3 etc.). Ignore the motion of the Earth and the Earth’s gravity. The gravity will bend the comet’s orbit a bit, such that some comets which would have just missed the Earth’s surface, by < 1 Earth radius, will now impact.
  6. Discuss whether asteroids have atmospheres.
  7. The temperature of an asteroid depends on its distance from the sun and its reflectivity. Why are brighter asteroids colder?
  8. Astronomers estimate that 40% of asteroids which cross the Earth’s orbit are extinct comets. Why are they extinct, where did they come from, and what are their orbits now?