1. 28.2 Life in the Solar System

2. Life as we know it… Carbon-based
Originated in a liquid water environment

3. The Moon and Mercury Lack
Liquid water
Protective atmospheres
Magnetic fields
So these bodies receive too much UV radiation, the solar wind, meteoroids and cosmic rays

6. Venus Too much atmosphere!
Its atmosphere is too dense, dry, scorching, hot

8. Jovian Planets Do not have a solid surface
Some researchers think that life could have evolved in their atmospheres

10. Pluto and the Jovian moons
Most are too cold
Jupiter’s moon Europa may have liquid water beneath its frozen surface
Saturn’s moon Titan has an atmosphere of methane, ammonia and may have liquid water – but it may be too cold

11. Europa’s surface

12. Enceladus – moon of Saturn, with water geysers

13. Mars

14. Mars Probably the planet most likely to harbor life
Water is scarce, but present
The atmosphere is thin
No magnetism or ozone layer
Atmosphere was thicker and planet was warmer in the past

15. Water on Mars
The Viking and Mars Global Surveyor show photographic evidence of flowing and standing water.
In 2004, the European Mars Express confirmed ice (water) at the poles.
Opportunity found evidence that water used to be very abundant.

16. Evidence of water on Mars

17. The “Face” on Mars

18. Life on Mars?
Even with the water and atmosphere and all of the probes that have been to Mars, no life or fossils of life have been found.
Viking robots tested Martian soil for bacteria and other life.
However, the orbiters have not widely surveyed the area.
Particularly, they have not surveyed the area near the polar ice caps.

19. What do scientists think about Mars today?
Biologists and chemists agree that no life exists on Mars today.
We will need to explore Mars more to learn if life existed there in the past.

20. Alternative Biochemistry
Would we necessarily recognize life if we saw it?
Could it be different from life as we know it?
Some scientists think that silicon might replace carbon in other lifeforms.
However, its bonds are weaker.
Maybe ammonia is used in place of water.

21. Alternative Biochemistry
You would have to have lower temperatures for ammonia to remain a liquid.
Colder temperatures are a problem.
There would not be enough energy to drive biological processes.