Imagining Other Earths

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Course Date: 08 September 2014 to 29 December 2014 (16 weeks)

Price: free

Course Summary

Are we alone? This course introduces core concepts in astronomy, biology, and planetary science that enable the student to speculate scientifically about this profound question and invent their own solar systems.

Estimated Workload: 5-7 hours/week

Course Instructors

David Spergel

David Spergel is the Charles Young Professor of Astronomy on the Class of 1897 Foundation and Chair of the Department of Astrophysics at Princeton University.  Spergel is best known for his work with the WMAP satellite that help determine the age and composition of the universe.  He is currently co-chair of NASA AFTA Satellite science team, a mission that aims to both determine the nature of dark energy and directly image planets around nearby stars.

Course Description

Over the past two decades, astronomers have discovered over a thousand planets around nearby stars.  Based on our current knowledge, it seems likely that there are millions of stars in the Galaxy that host Earth-sized planets in Earth-like orbits. What is the range of conditions for these planets to host life? In this course, students will engage with a wide range of concepts in astronomy, biology, chemistry, geology and physics with a focus on developing the background they will use need to think further about this profound question. We will explore the origin and evolution of  life on Earth, particularly in extreme environments, the properties of planets and moons in our Solar System,  the properties of stars and the newly discovered extrasolar planets.

Course assignments include two short papers describing proposed space missions to study nearby planets and to search for extrasolar planets and a final paper. In the final paper, students will have an opportunity to invent their own planetary system and describe it in terms of either the astronomy of how it was discovered, the properties of their planet and its host star, or the biology of life in the system. Papers will be circulated and evaluated by fellow students as part of the learning experience in the course; this will provide opportunities to develop students' abilities to think like a scientist by applying principles of scientific thinking, to learn new ideas from other students, and to creatively make new connections across different sciences and parts of the course.


  • Does Princeton award credentials or reports regarding my work in this course?

    No certificates, statements of accomplishment, or other credentials will be awarded in connection with this course.


Introductory Lectures
  • Lecture 1: The Universe is Big!
  • Lecture 2: What is life?
The Solar System
  • Lecture 3: Energy balance: What determines planetary temperature?
  • Lecture 4: Snowball Earth
  • Lecture 5: Planetary Atmospheres
  • Lecture 6: Earth, Venus and Mars: the goldilocks story
  • Lecture 7: Mars and the search for life
  • Lecture 8: The Moon and tides
  • Lecture 9: Titan and Europa: habitable moons?
  • Assignment 1: Report on Planetary Exploration Missions

Stars and Extrasolar Planets

  • Lecture 10: Kepler’s Laws Radial Velocity Searches for Planets
  • Lecture 11: Kepler Mission
  • Lecture 12: Imaging Other Planets
  • Lecture 13: Life of Stars
  • Lecture 14: Origin of the Elements
  • Lecture 15: Stellar Atmospheres Lecture 16: Jovian Planets
  • Assignment 2: Report on Astronomy Missions

Earth and the Origin of Life

  • Lecture 17: Formation History of the Earth and the Origin of Water
  • Lecture 18: Proteins, RNA, and DNA: Origin of Life
  • Lecture 19: Tree of Life
  • Lecture 20: Evolution
  • Lecture 21: Sex and the Origin of Complex Life
  • Lecture 22: Extremophiles
  • Lecture 23: Extinctions and Evolution Imagining Other Planets
  • Lecture 24: Aliens and the Future of Space Travel
  • Final Assignment: Design your own planetary system


Two lectures per week.

Two 5 page reports on proposed NASA and ESA exploration missions.

Final paper (5-10 pages) describing the properties of  a planetary system that you invent.

Suggested Reading

James Kasting, How to Find a Habitable Planet L. Weinstein and J.A. Adam,Guesstimation Neil F Comins,What if the Earth had Two Moons?

Useful websites:

Course Workload

5-7 hours/week

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