Planets, Stars, Galaxies, and the Universe



About Lesson 12

Prior to 1992, all of our knowledge of planets in the Universe came from the study of our own Solar System. Although we only knew about the planets orbiting our Sun, astronomers believed that planets should be common and assumed that most stars were likely to have their own system of planets. Taking this assumption one step further, some astronomers also considered that if planets are common, life may also exist elsewhere in the Universe. Then, in 1992, astronomers finally discovered planets outside of our Solar System. Since then, more than 1,000 planets have been discovered (or if you count the Kepler candidates, we're beyond 5,000!). Many of the new planets, however, are in systems unlike our own! While our theories for planet formation have had to be adapted, it is still considered possible that life exists elsewhere in the Universe.

Coronagraphic image of the star Fomalhaut showing disk ring and location of extrasolar planet b
Figure 12.1: Coronagraphic image of the star Fomalhaut showing disk ring and location of extrasolar planet b
Credit: NASA, ESA and P. Kalas (University of California, Berkeley, USA)

What will we learn in Lesson 12?

By the end of Lesson 12, you should be able to:

  • describe the habitable zone of a star and the likelihood for life to appear on various objects in the Solar System and in other systems;
  • describe how astronomers are searching for signals from other civilizations in the Galaxy.

What is due for Lesson 12?

Lesson 12 will take us one week to complete.

Please refer to the Calendar in ANGEL for specific time frames and due dates.

There are a number of required activities in this lesson. The chart below provides an overview of those activities that must be submitted for Lesson 12. For assignment details, refer to the lesson page noted.

Lesson 12 Requirements
Lesson 12 Quiz Your score on this quiz will count towards your overall quiz average.
Discussion: Near Earth Objects Participate in the ANGEL Discussion Forum: "Near Earth Objects".


If you have any questions, please post them to Piazza (not email). I will check that discussion forum daily to respond. While you are there, feel free to post your own responses if you, too, are able to help out a classmate.