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Life in the Solar Life in the Solar SystemSystem

Where have all the Martians gone?

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What is Life?• While we can list characteristics of

living organisms (and the book does), many non-living systems will exhibit many, if not all, of these characteristics– Is life about reproduction? Is a sterile

human alive? – Maybe it's about arising from

reproduction? If we took a copy of you by copying all the atoms of your body, would the copy be alive?

• The bottom line is:We have no useful definition of life.

http://www.lifeinuniverse.org/noflash/Lifedefinition-04-01.html

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Types of Life on Earth

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Origin of Life on Earth

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Life in Extreme

Environments:

Extremophiles

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What do we know?• We don’t know exactly what life is.• We don’t know exactly how life began.• What do we know?

– Where does life live? Almost everywhere on Earth.

– What are the requirements for life to exist and thrive?

• This isn’t too bad. After all, to find life, we first need to know where to look.

• Step 1: Decide what life needs and identify the places that meet these requirements so we know where to look.

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What is needed for life?

• The presence of liquid water• The elements needed for metabolism

and reproduction (biogenic elements)• A biologically useful source of energy• Suitable environmental conditions

http://www.lifeinuniverse.org/noflash/Conditions-04-02.html

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Limiting factor

• Biogenic elements (CHONSP…) are all over the Solar System (even in asteroids and meteorites)

• Sources of energy:– Sunlight (photosynthesis)– Many chemical reactions generated by heat– Others?

• Liquid water requires temperatures of 273-373 K (0-100 C).

• Environment– Mainly, no harmful UV rays

• Bottom Line: Follow the water

http://www.sciam.com/specialissues/0398cosmos/0398jakosky.html

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Follow the Water• What planetary bodies have liquid water?• Water needs warmth (273-373 K), so heat is

necessary.• Where does heat come from in the Solar

System?– Internal heat– Solar heat– Tidal heat

• That lead us to…– Earth (duh)– Mars– Europa

http://passporttoknowledge.com/solarsystem/life/water.html

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Mars

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Water on Mars

http://mars.jpl.nasa.gov/science/index.html

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Viking mission

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ALH84001

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Missions to Mars

• 2001 Mars Odyssey • 2003 Mars

Exploration Rovers• 2005 Mars Reconnaissance Orbiter• Beyond 2007

– Smart Lander and Long-range Rover – as early as 2007

– Sample Return – as early as 2011, likely 2014

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Mars Exploration Rovers

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Europa

http://www.spaceviews.com/2000/04/14b.html

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Missions to

Europa?

http://www.jpl.nasa.gov/europaorbiter/

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Questions

• How important will it be if we discovered other life in our Solar System?

• How would we know it wasn’t life from Earth?

• Is NASA right in concentrating much of its resources on searching for life? (ie., is Europa more important than Io?)