Planetary Predictors of Extraterrestrial Life

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  • 1:40 Mars
  • 2:09 Jupiter's Moons
  • 3:12 Saturn's Moons
  • 4:04 Lesson Summary
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Lesson Transcript
Instructor: Amy Meyers

Amy holds a Master of Science. She has taught science at the high school and college levels.

Investigate what is needed for life to exist anywhere and the implications for life in our solar system beyond Earth. Consider Mars and some of the moons of Jupiter and Saturn, including Europa, Callisto, Ganymede and Enceladus.

Little Green Men

Hello. My name is <untranslatable>, but you can call me Greenie. I am from outer space. I don't want to tell you my exact location, because I don't like people to visit me. My house isn't very clean. But I love to visit you! You see signs of my visits nearly every time you stand at a grocery store checkout stand. Now, those headlines about me aren't true; I'm perfectly harmless. Some people don't think I even exist. Other people don't think there's any extraterrestrial life anywhere in your solar system, much less the universe. But as your two renowned scientists - Carl Sagan and Stephen Hawking - have said, it would be improbable for life not to exist somewhere other than Earth. Let me help you examine extraterrestrial life and then take you on a tour of where in your solar system it might exist.

To know if life exists anywhere in the universe other than Earth, you need to decide what life is. Is life an intelligent, thinking being? Or is it just something that can reproduce, adapt to its environment and metabolize things? If you think life is just the latter, then it is much more likely you will find life elsewhere in the solar system. It is thought that bacteria exist elsewhere in your very own solar system!

Once you decide what life is, you need to decide what something needs to live. Most scientists agree that life needs liquid water to survive. With that in mind, let's take a tour of your solar system, and I'll show the places in the universe that all seem to have that one criteria that is needed for life! First stop: Mars.


Scientists believe that as recently as 3.6 billion years ago - when life began on Earth - there was liquid water on Mars. Although today the planet is dry and most of its water is locked up in the polar ice caps, scientists believe that at one time oceans covered the planet. During that time, the planet could have evolved life. Any life on Mars today is probably under the surface in a hidden water source.

Moons of Jupiter

Let's leave Mars and fly to the moons orbiting Jupiter.


This is Europa, the sixth closest moon to Jupiter. Europa has a layer of ice covering it. Scientists believe there is liquid water under the ice and that life may exist there - just like the life found in the deep oceans of Earth.


Callisto is another moon of Jupiter. Callisto's atmosphere is made of carbon dioxide and probably oxygen. Callisto may have water 100 kilometers under its surface where life may exist. This is less likely, though, than the possibility of life on nearby Europa.

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