ASTR 380 Our Solar System: A worked Example
Themes in Our Solar System Temperature Trends Energy for Life Rocky, Gassy. Icy Atmospheres Moons Stability Special Conditions Winning the Lottery
Temperature Trends in our Solar System The Sun is the primary source of energy in the Solar System. As a first approximation, energy in = energy out equilibrium Temperature Planets further from Sun are colder. Temperature unit: Kelvins 373 K = boiling water 273 K = 32 F Freezing 77 K = air freezes
Temperature Trends in our Solar System Mercury : 670 K on the day side 70 K on the night side Venus: 740 K on surface little variation in day-night BUT should be 350 K except for atmosphere -- greenhouse effect Earth: average 288 K low 225 K high 325 K But should be 255 K average if no atmosphere
Temperature Trends in our Solar System Mars: average -- 215 low 135 high 290 Jupiter: average 150 K depends on depth in atmosphere Saturn: average 130 K depends on depth in atmosphere
Temperature Trends in our Solar System #1 effect is heating by Sun but day-night and seasonal changes makes for variations! Atmospheres tend to warm planets and smooth out variations Venus 740K Not 350K There remains a clear trend: 1 3 AU is best for life
Temperature Trends in our Solar System Secondary Effects: Internal heat within planet: on Earth Geothermal Even if the Earth were cold Geothermal activity would continue Arises from Earth s molten core and mantle The heat comes from radioactive decay of elements in the mantle and core!
Temperature Trends in our Solar System We can see that geothermal activity was present on Venus, Mars, and even our Moon. But for bodies significantly smaller than the Earth, radioactive decay does not generate enough heat to keep the core molten. Olympus Mons on Mars We know that the Moon is solid We suspect that Mars is solid We expect that Venus is still active! Moon
Temperature Trends in our Solar System Tides can heat Moons: Io, a moon of Jupiter is the prime example in our Solar System Has observed lava flows with hot-spot temperatures of 1300-1600 K Io is a rocky moon the other big moons of Jupiter are icy
Temperature Trends in our Solar System Tides can heat Moons: Titan, a moon of Saturn may be a second interesting example. Methane volcanoes indicate that its interior is kept warm. Compare to its surface temperature of 94 K!
Basic truth: Life requires energy! Energy for Life Solar, geothermal, chemical. Energy to enable the ordered activity that is life. From Earth s example, life exploits all available energy. Tubeworms near a vent But life is limited by the availability of energy. Bacteria 400 meters Below the seabed Fundamental unknown: Can life originate in isolated islands of energy? Or does it require abundant, widespread availability?
Rocky, Gassy, Icy Theme: rocky, gassy, and icy planets and dwarf planets in our Solar System. Rocky: close to Sun; within 4 AU Gassy: middle distance from Sun; 5 30 AU Icy: far from Sun; 30 AU an beyond Temperature and availability of material during formation cause this trend of planet type with distance.
Rocky, Gassy, Icy Rocky: formed in the inner Solar System after most gas gone modest amount of rocky material so no big planets Rocky planets too small to capture gas at birth Atmosphere created from gases in rocks and impacts of comets. Early heat on planet kept away ices and gas.
Rocky, Gassy, Icy Gassy: grew in places where rocky cores could attract gas rocky cores at center primarily hydrogen and Helium gas lots of material in this region in birth nebula
Rocky, Gassy, Icy Icy Dwarf Planets: grew in places with rock and ices little material so never grew big could not hold into hydrogen and helium so no big atmospheres Big cousins of comets and perhaps millions of Kuiper-Belt objects Plot of known Kuiper Belt Objects Artist s concept of Sedna
Atmospheres Jupiter s Atmosphere Solar System Atmospheres have three origins: 1. Gas captured during birth of planet Gas Giant planets did this! Hydrogen, Helium dominant 2. Outgassing from molten rock on the surface terrestrial planets carbon Dioxide, sulfur dioxide, water, methane, ammonia volcanic activity continues this process Venus Atmosphere 3. Comet impacts happened on all planets but most important for terrestrial planets
Atmospheres Solar System Atmospheres have three origins: 1. Gas captured during birth of planet 2. Outgassing from molten rock on the surface 3. Comet impacts
Atmospheres BUT. Why are Venus, Earth and Mars so different? Venus probably kept all of its atmosphere Mars lost most of its atmosphere Earth kept just the right amount due to the collision that made the Moon.
Atmospheres Mars size impactor completely destroyed Earth surface all molten Atmosphere ripped off Moon reform in orbit from debris Earth crust reforms
Demos Moons The terrestrial planets have rocky moons, and few of them The gas giants and icy dwarf planets have rocky and icy moons sometimes many moons. Phobos There are different stories for many of the planets: Mercury no moons too close to Sun Venus no moons --? Earth 1 big moon created by a collision Mars 2 small moons captured asteriods Gas Giants many moons some formed in a mini-solar system during birth, others captured Moons of Uranus
Stability Earth life required time to form and to evolve. Life began on Earth 200-400 Million years after the crust became cool. About 1 Billion years after formation. Around 1.6 Billion years cyanobacteria Around 3.4 Billion years multicell organisms Earth life required sufficient stability to maintain life but enough change and variability to drive evolution.
Special Conditions Earth life required: rocky surface liquid water right amount of atmosphere right temperature range multi-billion year stability It is even argued that life required our big Moon to get rid of the excessive atmosphere at the collision to raise large tides to drive evolution
Winning the Lottery One could argue that life on Earth is a One in a million One in a billion Or larger Long shot. But we are here so may be it had to be.. Or maybe we are the one winners of the life lottery in the millions of planets in our Galaxy and the millions of galaxies in the Universe!