Astronomy 1110

Homework #5 - Solutions

Astrobiology and Spacecraft

Due at start of class, Thursday, July 6.

1. Different Views on the World?
The largest telescope in the world is the Arecibo Radio Observatory in Puerto Rico, 1000 feet across (one of the ones Jodi Foster used). The largest optical telescope (using visible light) are the 10-meter Keck telescopes in Hawaii. The largest telescope in space is the 2.4-meter Hubble Space Telescope. The highest resolution images of the Jovian satellites, however, are from the Galileo spacecraft. Explain how these four telescopes are different, and how they are the same.

Arecibo - a giant radio observatory. It can point only straight up, but it's the largest dish in the world, so can detect sensitive signals. Old technology, brute force, and works well.

Keck - the premier optical (& infrared) telescopes in the world. Although they don't have the resolution of Hubble, their mirrors are much bigger and they can gather more light (25x) in a shorter time. Since they're on the ground, they're cheaper -- you could build 25 Kecks for the price of one Hubble.

Galileo - not a large telescope (only a few inches across), but it's the only one which can get near Jupiter to look at it. It can look from different angles than we can from Earth, can look close up, and can also directly measure quantities like the magnetic field.

2. Evidence of our Civilization
Discussion Question 1, Ch. 13 in the text (p. 397)

Over a period of 10,000 years, there will probably be many remains from human civilization. Buildings, roads, airports, rusted Chevys, oil tankers, cemetaries - you name it. Erosion from wind, air, and water will be the major processes -- in addition to chemical breakdown, such as rusting of metals (until they dissolve completely). Evidence like paper will probably be gone quickly. We know that a lot of these buildings, roads, etc. will stick around for 10,000 years, because we see them preserved from previous cultures already: Pompeii (2000 years ago), ancient Greece (2500 years ago), and so forth.

Over a 10 million year period, we might have a harder time. The Earth resurfaces by plate tectonics over about 200 million years, so the evidence will still be on the surface -- but erosion will have taken a dramatic toll on most of it. Structures such as buildings and roads will be long gone -- except for the ones that are buried beneath sand, water, or mud, just like dinosaur bones are today. Some evidence for radioactive materials may still be around, since these metals usually differentiate and fall toward the center of the Earth, and don't usually concentrate themselves on the surface. In the geologic record, there may also be evidence of changes in carbon dioxide levels or global pollution -- seen as a thin layer put down in the rocks on the surface and the ocean.

3. What is life?
Write your own definition of life, in several sentences. Is there a difference in your definition between plants and animals - or other kingdoms? Should there be? Would a self-replicating robot (a robot, which is built to build another robot from scratch, which builds another one, each of them getting better and better) fit your definition of life? Should it?

Some characteristics of life on Earth:

If a robot fits enough of these definitions, it might be considered life. But some people might impose another criterion: that it's not `artificially made' by humans.

The difference between plants and animals? Perhaps arbitrary or not, depending on your own definition.


Dr. Henry Throop, University of Colorado / throop@broccoli.colorado.edu

Last modified 6-Jul-2000