Astronomy190 - Topics in Astronomy Astronomy and Astrobiology Lecture 3 : A Tour of the Solar System Ty Robinson

Questions of the Day What three characteristics must a world have in order to be considered habitable? Which worlds in the Solar System are least likely to harbor life? Why? Which are are most likely to harbor life? Why?

Tychonic System

Motions of the Heavens

Retrograde Motion

Places for Life in Our Solar System

What Are Life’s Environmental Requirements? Building Blocks –The environment must have a source of molecules from which to build living cells Energy –The environment must have a source of energy to fuel metabolism Water –The environment must have a liquid medium, most likely water, to transport molecules needed for life.

Building Blocks Life needs a set of chemical elements with which to make the components of cells. –Earth life uses about 25 of the 92 naturally occurring chemical elements This requirement can probably be met (somewhere) on most bodies in our Solar System.

Energy Sources Life requires an energy source to support metabolic processes that break down molecules and form new ones. –Sunlight (fuels photosynthesis) –Organic molecules (eating) –Chemical energy (reactions with iron, sulfur, hydrogen compounds)

Solar Energy Decreases With Distance. In the outer solar system, other energy sources may be needed.

A Liquid Life requires a liquid that can: –Dissolve organic molecules, making them available for chemical reactions within cells –Allow for transport of chemicals in and out of the cells –Engage in metabolic reactions e.g. water molecules are necessary for reactions that store and release energy in the cell

It’s liquid over a large temperature range Temperatures at which it is liquid are high Water’s Advantages

Questions? Why should the temperatures over which a substance is liquid be relatively high? high temperatures cause complex molecules to break apart organisms prefer to live in warmer conditions chemical reactions proceed faster at higher temperatures cold temperatures cause freezing

Terrestrial Planets - Interiors Crust-mantle-core structure. Trend for density to increase with the planetary size of the object (even when corrected for compression-effects) Mercury is an exception to this rule.

The Moon and Mercury 

Venus 730K surface (~860F) 93 bar atmosphere Sulfuric acid clouds No intrinsic magnetic field. 

Earth and Mars ?

Earth and Mars

Is there water on Mars?

Evidence for Past Water on Mars

Evidence for Current Water (and Life?) on Mars?

Questions? Given that frozen water has been found on Mars’ surface, where should we go to look for liquid water on Mars? near the Martian equator, where temperatures are warmer under the polar ice caps at the bottom of large craters on Mars’ surface into Mars’ subsurface

Outer Planets

Interior Composition

Jovian Planet Characteristics Jupiter, Saturn, Uranus and Neptune are “liquid planets”, they have no solid surfaces Their outer layers are made of “Sun-stuff”, seen at much cooler temperatures. The atmospheres are strongly convective and have clouds that are driven by winds generated from solar and internal heating.

The Habitability of Jovian Worlds Pros: –There are probably liquid water clouds at a depth of ~100km. Cons: –Strong vertical winds Carry complex organic molecules, bacteria, to depth and destroy them

The Jovian Moons

Io 

Europa Anomalies in magnetic field measurements near Europa suggest a “conducting liquid” below the surface of the satellite. Surface features indicate “warm” slushy ice at shallow depths.

Titan

Enceladus

Tiger Stripes

Enceladus’ South Pole

Questions of the Day What three characteristics must a world have in order to be considered habitable? Which worlds in the Solar System are least likely to harbor life? Why? Which are are most likely to harbor life? Why?