Life in the Solar System Basic Requirements for Life 1. Chemical elements to make biological molecules. On Earth these are mostly C, H, O and N 2. Source of energy for metabolism. This can come from a variety of sources including photosynthesis, geothermal, chemical etc. 3. Liquid solvent for biological reactions to occur in. On Earth this role is taken by water The building blocks of life are common and are present throughout the solar system A variety of energy sources is also available Water, however is not always found as it can only exist under certain conditions of temperature and pressure Conclusion? The Role of Water in Life The search for Life is essentially the search for water! Where there is water there could be Life! 1. Dissolves biological molecules 2. Transport of molecules across cell membranes 3. Enables metabolic reactions to occur within cells 1
Advantages of Water 1. Excellent Solvent dissolves many things 2. High Heat Capacity absorbs heat without changing temperature 3. Large and High Liquid Range is a liquid at relatively high temperatures (where metabolism can proceed quickly) and over a wide range of temperatures 4. High Surface Tension forms droplets which concentrate things 5. Expands on Freezing ice floats on water preventing bodies of water freezing completely Water is a polar molecule Hydrogen Bonding in Water Hydrogen Bonding and the Double Helix δ+ There are strong intermolecular forces between molecules called hydrogen bonds δ+ δ+ δ+ δ+ Alternatives to Water Substance Freezing Temp (ºC) Boiling Temp (ºC) Range (ºC) Water (H 2 O) 0 100 100 Ammonia (NH 3 ) -78-33 45 Methane (CH 4 ) -182-164 18 Ethane (C 2 H 6 ) -183-89 94 with exception of ammonia all are poor solvents compared to water most have much narrower liquid ranges (except ethane) most are liquids at much lower temperatures which means very slow reaction rates (drop in rate by 50% every 10 ºC drop in temperature) solids are all denser than water ammonia probably most likely alternative Exploration for Habitable Environments in the Solar System Basic Approaches: Telescope studies from Earth or Orbit Robotic spacecraft Human Visits only the Moon! Nearly all studies to date carried out telescopically or using robotic space probes! 2
Mauna Kea, HI The Hubble Space Telescope (HST) Elevation: 13,700 ft Chemical compositions are determined from the spectroscopy of reflected sunlight from a body By comparing the spectrum the object with the spectrum of materials in a lab we can determine the chemical composition of surface or atmosphere of a planet or moon! The Spectrum of Europa Europa has an icy surface! Types of Space Mission 1. Flyby takes a quick look as it flies past planet once 2. Orbiter place probe in orbit around planet for extended study 3. Lander land on surface or parachute into atmosphere of planet 4. Sample Return return sample from planet to Earth 5. Human Visit humans set foot on planet 3
Voyager Flybys to Jovian Planets The Magellan Venus Orbiter Mapped the surface of Venus with radar in the 1990 s The Mars Exploration Rovers The Stardust Mission to Comet Wild 2 Currently searching for evidence of water on the surface of Mars in the past Jan 2004: collected dust from comet The only human visit the Apollo missions to the Moon! Jan 15 th 2006: Samples safely returned to Earth 4
Lunar Reconnaissance Orbiter (2009) Apollo 12 astronaut visiting Surveyor 3 Apollo 12 Landing Site Mercury and the Moon Ice on Mercury and the Moon? Lack atmospheres so liquid water cannot exist! Ice deposits may build up inside polar craters which are in permanent darkness Controlled Crash of Lunar Prospector onto Moon s Surface July 31 st 1999 Attempted to liberate water vapor from the surface d t t d 5
LCROSS Mission to Moon The Lunar South Pole Oct 9th 2009 Rocket fired into the polar crater Cabeus guided by shepherding satellite! Shepherding satellite then flew through impact debris and took pictures before crashing into the surface itself! Bulk Properties of Venus Summary 1. Venus is 28% closer to the Sun having an orbital period of 225 Earth days 2. Venus is roughly 95% the size, 82% the mass of the Earth and has a very similar density. Because of the similarity its is often referred to as Earth s Twin. However, appearances can be deceiving! 3. Venus is extremely reflective having an albedo of 59% Surface hidden by thick, highly reflective atmosphere 6
Svante Arrhenius on Venus (1918) Expected average surface temperature based on distance from the Sun (0.72 AU) is 318 K or 113 F Low enough for liquid water to exist! "The temperature is not so high as to preclude a luxuriant vegetation...the vegetative processes are greatly accelerated by the high temperature. Therefore the lifetime of organisms is probably short... Radio emission from the surface indicates a surface temperature of 733 K or 860 F Hot enough to melt tin, lead and zinc! Why so hot? Atmospheric Composition Runaway Greenhouse Effect 96.5% CO 2, 3.5% N 2 Atmospheric Pressure at Surface P = 90 atmospheres (atm) 1 atm = pressure at sea level on Earth Pressure experienced 2900 ft beneath sea! Very thick and massive! 7
Highly reflective clouds are made of droplets of concentrated sulfuric acid (H 2 SO 4 )! Venera Landers: the surface of Venus Most common rock basalt! The surface of Venus is far too hot for liquid water to exist! Why Venus and Earth so different? 8
Jovian Planets Lightning in Jovian Atmospheres Giant Urey-Miller Experiments? Asteroids Problem: Lack solid surfaces to accelerate complexity! Comets Too small for liquid water to exist! 9