nature of habitability
The Nature and Evolution of Habitability A discussion of Bennett et al. ... Geller Chapter Overview Nature and evolution of habitability Sun¡¦s habitable zone Comparative planetary evolution especially Venus Surface habitability factors Future of life on Earth Habitability: Introduction Define ¡§habitability¡¨ Anthropocentric perspective Astrobiological perspective (capable of harboring liquid water) Key physical and chemical features of habitability Surface habitability Temperature Source of energy Liquid water (present and past) Biological macromolecules (e. ... , sugars, nucleotides) Atmosphere and magnetosphere Comparative Planetary Evolution Concept of a Habitability Zone Definition of habitability zone (HZ) ¡§Region of our solar system in which temperature allows liquid water to exist (past, present and future)¡¨ Phase diagram for H2O Retrospective analysis of HZ using the terrestrial planets as case study Mars, Venus and Earth Prospective analysis of HZ Luminosity of the Sun Definition of luminosity (watts/m2) Sun¡¦s luminosity has been changing: earlier in its evolution, luminosity was only 70% of what it is today (how could temperature be maintained over geological time) Future for luminosity Remember star sequence from lab and lecture 2-3 BY, luminosity will place Earth outside habitability zone Distance from the Sun Terrestrial planets ¡V heat mostly from Sun Jovian planets ¡V 2/3 of heat from interior (all planets originally had internal heat source due to bombardment) Heat from Sun is inversely proportional to distance2 or heat energy = k*1/(distance)2 Heat falls off rapidly with distance Habitability Zone of Our Solar System Exploration of Mars, Venus and Earth provides a framework to establish a HZ in terms of water Venus (0. ... 5 AU): oceans primordially Thus, range of habitability around stars like Sun is 0. ... 5 AU Zone of ¡§continuous habitability versus zone of ¡§habitability¡¨ (which is more narrow?) needs to maintain habitability for billions of years Continuous Habitability Zone of Our Solar System Outer edge of HZ must be less than Mars (1. ... 2 AU in breadth Habitability Zone in Our Galaxy Use the range from our solar system as a basis for analysis In our solar system, 4 rocky planets that orbit the Sun from 0. ... 4 AU apart If typical, likelihood of other solar systems having continuous habitability zone is just width of the zone divided by the typical spacing 0.