Life in the Solar System ... and Beyond • While Earth is the only confirmed body with life in the Solar System, we have found many other bodies which may support life • Today, we will talk about some of these worlds and the life that may exist there • Knowledge of life in our Solar System also lets us estimate what life may exist beyond BestSolar Candidates System Inventory for Life? 1 star Sun 4 terrestrial planets Mercury, Venus, Earth, Mars 4 gas giant planets Jupiter, Saturn, Uranus, Neptune 7 large moons Moon, Io, Europa, Ganymede, Callisto, Titan, Triton small moons, asteroids, Phobos, Ceres, Amalthea, comets, KBOs, dust Rhea, Enceladus, Titania, Proteus, Pluto, Charon Mars • No hard evidence for any lifeform on the surface, though only Viking landers looked • Much more likely in the distant past when Mars was warmer and wetter • May still be very small microbial life near water ice deposits around the poles or a few feet below the surface 1 Jupiter? • The idea is a bit far fetched, but there are layers in Jupiter's atmosphere where temperatures and pressures would be right for liquid water • Any life that developed in the atmosphere would float through the different layers, much like life in Earth's oceans • Very unlikely, but possible Europa and Enceledus • Of all the gas giant moons, Europa and Enceledus offer the best possibilities • Each moon, especially Europa, shows evidence for a large amount of liquid water • Life systems much like the deep sea vents on Earth may exist on both worlds • It will take quite a bit of time and effort to know for sure Titan • Titan seems to have all the proper ingredients for life, but not high enough temperatures • A large amount of hydrocarbons reside in the atmosphere and surface • Some amino acids are also detected • If Titan were warmer, it may be an ideal location for life 2 Beyond the Solar System The Habitable Zone • When looking outside our Solar System, it is easiest to think about zones where life could survive • The habitable zone usually corresponds to locations where liquid water can exist • The habitable zone is 'not too hot' and 'not too cold', but should be just right for life The Habitable Zone • Since different stars have different brightness and temperatures, the size and location of the habitable zone can change Problems with the Habitable Zone • There has been some dispute of the accuracy of the habitable zone • After all, there are locations in our Solar System well outside the HZ where liquid water may exist • Despite the argument, the habitable zone is the most favorable location for life to occur in a star system 3 Finding the Right Star • While it is easiest to think about life around a Sun-like star, that doesn't have to be the case • However, there are some stars which make their surroundings quite inhabitable • Some small, red M dwarfs have violent flaring activity • Large, massive O/B stars have strong winds and put out more ultraviolet and X-ray Artist concept of a flaring M dwarf radiation The Galactic Habitable Zone • The HZ concept can be expanded to the galaxy as a whole • The interior of the galaxy is a very energetic, very unstable place • The extremities of the galaxy contain too few heavy elements for Earth-like planets to form What About Intelligent Life? • One of the most interesting and controversial branches of astronomy is the Search for Extra- Terrestrial Intelligence • The SETI Institute is basically a large listening program, trying to find signals from aliens • The search continues... 4 Can They Hear Us? • Radio and television signals have been leaving Earth for over 50 years • If anyone within 50 light-years is listening, then they could have detected us • Odds of an intelligent civilization being that close is very slim • Also, our signals are not concentrated - instead they spread out thinly in all directions Can We Hear Them? • Under current technology, it would be hard to hear them unless the signal was directed straight at us • Unfortunately, they have no reason to send signals, since most of them would not know we exist • Improvements in tech and facilities over the next decade will let us here the slightest whispers of civilization SETI • The SETI Institute is a non- profit, privately funded organization • They use radio data which comes primarily from the Arecibo dish in Puerto Rico and the 100m radio telescope in Greenbank, West Virginia • A new array of telescopes is being built in California called the Allen Telescope Array, which will be fully devoted to SETI 5 Are They Even Out There? • One of the ultimate scientific/philosophical/ religious questions is 'Are We Alone?' • From a sheer numbers standpoint, the odds of only Earth possessing intelligent life are essentially impossible • Each galaxy contains 100's of billions of stars and there are 100's of billions of galaxies out there The Drake Equation • One quick and easy way to estimate the number of civilizations in the galaxy is the Drake equation • Frank Drake developed the equation in the 1960's • Based on a set of astronomical and biological factors, the equation will tell you the number of intelligent, communicating civilizations in the galaxy The Drake Equation * N R f p ne f l fi f c L N # civilizations with detectable electromagnetic emissions R* rate of star formation (stars/year) fp fraction of stars that are stable with planetary systems ne # of worlds/system with environment suitable for life fl fraction of planets on which life develops fi fraction of life-bearing planets on which intelligent life arises fc fraction of intelligent civilizations revealing existence L length of time civilizations release detectable signals (years) 6 Rate of Star Formation • This factor we have a pretty good estimate for • Stars are constantly being born in the galaxy, and the rate at which they are born will tell you how many are available • The galaxy has between 100-200 billion stars, and is about 10 billion years old Dusty star formation regions • Therefore, the average rate (REAL PICTURE!) is about 10-20 stars per year Fraction of Stable Stars with Planets • Not all of the stars in the galaxy will be stable and not all of the stars will have planets • We have only begun to find planets around stars, but the results are quite encouraging • It is most likely a natural process for stars to have planets • Earth-like planets are still waiting to be found Number of Worlds with Conditions Suitable for Life • This factor is the number of planets or moons in a solar system that may be able to support life • Habitable zone considerations come into play with this factor • As we already discussed, there may be five or six other places that could support life 7 Fraction of Worlds with Life • Of all the planets or moons in the star system, this is the fraction which actually develop life • We know of ONE planet with life in our Solar System • If you include all the planets and large moons, then this number is something like 1/15 Fraction with Intelligent Life • Of those planets which have developed life, this is the fraction which has developed 'intelligent' life • For our Solar System, Earth is the only case with life and it developed intelligence • The definition of 'intelligence' is somewhat hazy - some would argue the case for humanity Fraction with Communicating Life • Of the worlds with intelligence, what fraction will produce a signal that can travel through space? • Our civilization has been around thousands of years, but we have only been communicating for ~50 years • The development of technology will likely lead to some sort of signal into space 8 Length of Time Civilization is Communicating • This is one of the hardest factors to estimate, since we have no good reference • Our civilization has been communicating for ~50 years, but how much longer will we be sending signals? • This factor depends on how long the civilization survives, and how long its signal leaks into space So How Many? * N R f p ne f l fi f c L • Even conservative estimates for each of these factors produce a sizeable number of intelligent civilizations in the galaxy • With advances in technology, it is likely that IF there is a signal to be found, it will be found in our lifetime • We will do an exercise on Friday involving the Drake equation and the possibilities of alien life 9.