Astrobiology: the origin, evolu on, distribu on, and future of life in the universe
Outline of this class: Life, extreme life on earth Where else in solar system could life exist? Mars, Titan& Europa, Habitable zone (review), difficulty with es ma ng probability of life, Drake equa on for es ma ng likelihood SETI: Search for Extraterrestrial Intelligence
Reminder: • No class this Wednesday, Happy Thanksgiving! • Next Monday: primarily review • Next Wed: YOU each do class presenta on (30 % of your final)
• Mon, Dec 9 Final exam. Would you all like to follow this with a potluck supper? (Cole e and I will contribute major items!) No need to cook something! What defines life?
• the capacity to grow, • metabolize (convert food to energy) • respond (to s muli), • adapt • reproduce
What is necessary? Recent discoveries of life under extreme condi ons on earth (extremophiles) show that neither sunlight nor oxygen are required yellowstone
Yellowstone Na onal Park: microbes live in boiling water (90 C). Other pools are extremely acidic, yet microbes and bacteria thrive there Life in extreme condi ons on earth
Black smoker, deep in the ocean: an example of life that has no need of sunlight: From vents deep in the ocean hydrogen sulfide provide energy for bacteria, which in turn feed clams, tube worms (up to 10 long) Bacteria up to a mile underground: water seeps in, and bacteria generates energy from chemical reac ons
A NASA favorite: Tardigrade (water bear) that survive at temps from absolute zero to above boiling, pressures up to 6x that of deepest ocean trenches, ionizing radia on. They can go without food or water for more than 10 years and then revive.
(Less than 1 mm long) Are there other places in our solar system that might harbor life?
Temperatures that allow liquid water may be very important
We discussed the Goldilocks idea for Venus (too hot), Mars (too cold), Earth (just right) Could there have been life on Mars in the distant past?
1996: Mar an meteorite found on earth, could it be possible fossil life from Mars? Current thinking is that this is not a fossil, but it raises interes ng ques ons What about other places? The moons of gas giants Moons of Jupiter (Ganymede, Europa) and Saturn (Titan)
NASA missions in past 20 years have revealed a great deal:
Europa: covered with ice, possibly liquid beneath the ice Titan: has atmosphere, and liquid surface (but not water…) Europa: One of 4 Jupiter moons easily seen with small telescope - About the size of earth’s moon - Orbits Jupiter in about 4 days – so rela vely close to Jupiter
NASA Galileo mission, launched 1989, reached Jupiter 1995, orbited with flybys of moons un l 2003
Found the surface of Europa is covered in ice, long fractures – suggests liquid water underneath ( heated by strong des from Jupiter)
Liquid water: raises possibility of primi ve life? Next, an Aside on des: Aside on des:
Earth- moon: ocean des caused by gravity ( force = mass, inverse distance)
Tides consume energy (fric on): lead to dal locking
Example of dal locking: moon keeps one face to the earth all the me) Surface of Europa, from the Galileo mission, showing “ice ra s”
Scale: This image is 20 by 50 miles
A theore cal model of possible ocean on Europa. (Rick Greenberg, UA) NASA Cassini mission to Saturn:
Launched 1997, arrived 2004 Cassini made mul ple flybys of Venus, Earth and Jupiter to gain the required energy to reach Saturn
It carried a probe, named Huygens, that parachuted to the surface of the moon Titan in 2005, sending back images of the descent
Cassini is s ll orbi ng Saturn, sending back data Saturn’s largest moon: Titan View of surface from Huygens probe, which parachuted to the surface
atmosphere
Surface from about 30 km Surface: Titan: further explora on suggest lakes of liquid methane, ethane: a “water cycle” than involves no water!
While these are interes ng places, we have no evidence of any form of life on them. Let’s turn to the stars. Is extrasolar intelligent life likely? Let’s start with a sta s cal es mate exercise: how many le -handed, 8 year old boys are there is the US right now? how many le -handed, 8 year old boys are there is the US right now?
1. Popula on of the US, P:
2. Frac on of males, Fm
3. Frac on of people who are le handed Fl
4. Frac on of popula on who are 8 years old F8
•Answer = P * F m* Fl* F8 Scien fic Nota on: or handling big numbers scien fic nota on: 1,000 = 103 = one thousand 1,000,000 = 106 = one million 1,000,000 = 109 = one billion
100 = 102 1000 = 103 , 102 x 103 = 105 (add the exponents) (2 x 102) x (3 x 103) = 6 x 105 105 / 103= 102 (subtract the exponents)
Our CCD at 0.9m was 4 x 103 by 4 x 103 pixels. How many pixels total? The Drake Equa on: sta s cal es mate of the number of intelligent, communica ng civiliza ons in our galaxy right now
1. Number of stars in our galaxy 2. Frac on of stars that have planets around them 3. Number of planets per star that are capable of suppor ng life (see habitable zone)
4. Frac on of planets where life evolves 5. Frac on of these planets where intelligent life evolves 6. Frac on of intelligent life that communicates 7. Frac on of a planet’s life me during which the civiliza ons communicate
N equals the product of all these factors! 1. How can we measure the number of stars in our galaxy?
(This isn’t an actual picture of our galaxy. Why?) How do we measure the number of stars in our galaxy?
We can use the law of gravity to measure how much mass is within our galac c orbit.
Vc = velocity of sun around galac c center r = distance from sun to galac c center
We divide this mass by the average mass per star to get the number of stars Current best number: 2-4x1011 stars (200 to 400 billion) 2. What is the frac on of stars that have planets?
Kepler Project: indicates that prac cally all sun-like stars have planets
Although Kepler looks at a very small frac on of the Milky Way galaxy, it should be representa ve of most Is is appearing that the majority of planets are more earth-like than Jupiter-like h p://astro.unl.edu/naap/habitablezones/anima ons/ stellarHabitableZone.html 3. What number of planets are able to support life?
• Recall the habitable zone concept – warm enough for liquid water
• NOV 4 2013: KEPLER PRESS RELEASE: “one in five stars like the sun is home to a planet up to twice the size of Earth, orbi ng in a temperate environment. “ The other factors ( 4 through 7 ) are up to you:
Values you get?
Note that this ONLY addresses our galaxy: there are about as many galaxies in the known universe as there are stars in our galaxy! So, how far might the nearest earth-like planet be?
If there is intelligent life there, do they know about us? (the “I Love Lucy” effect) Listening for intelligence: from Project Ozma (1960) to SETI (today) SETI Project: search for intelligent signals
SETI@home: 1998, ci zen science program, using personal computers to help with data reduc on, also support from Planetary Society (private group)
Small percent of me devoted to this search, SETI Project: the Allen Telescope array
• Need for more telescope me: proposal to build up to 350 small radio telescopes,
• supported by Paul Allen (Microso founder), located at Hat Creek Obs, CA
• Went on line in 2007, only 3 telescopes in place
Survey 1,000,000 “nearby”stars for SETI emission
Survey the galac c plane for very powerful transmi ers What sort of signal is SETI looking for?
•The Arecebo telescope does not track the sky, so a exterrestrial signal will dri through its beam.
•We might expect an intelligent exterrestrial signal to be narrow in frequency, rather than covering a broad range
•If the signal contains informa on, it will be pulsed
•Since planets (like us) probably rotate, it may show a Doppler shi , or change in frequency – and this would include pulses
•If we detect a signal, how will we decode it? Needless to say, we haven’t heard anything… do you think we will? How will we decode it?