28.2 Life in the Solar System

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

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

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

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

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

Europa’s surface

Enceladus – moon of Saturn, with water geysers

Mars

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

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.

Evidence of water on Mars

The “Face” on Mars

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.

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.

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.

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.