Life in the ... and Beyond

• While 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

4 terrestrial , , Earth,

4 planets , , ,

7 large , , , , , ,

small moons, , , , Amalthea, , KBOs, dust , , , , ,

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 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 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 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 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