Astrobiology: the origin, evolution, distribution, and future of life in the universe

Reminder:

• No class this Wednesday, Happy Thanksgiving!• Next Monday: primarily review• Next Wed: YOU each do class presentation (30 % of your final)

• Mon, Dec 9 Final exam. Would you all like to follow this with a potluck supper? (Colette and I will contribute major items!) No need to cook something!

Outline of this class:Life, extreme life on earthWhere else in solar system could life exist? Mars, Titan& Europa, Habitable zone (review), difficulty with estimating probability of life,Drake equation for estimating likelihoodSETI: Search for Extraterrestrial Intelligence

What defines life?

• the capacity to grow, • metabolize (convert food

to energy)• respond (to stimuli), • adapt • reproduce

What is necessary? Recent discoveries of life under extreme conditions on earth (extremophiles) show that neither sunlight nor oxygen are required

yellowstone

Yellowstone National Park: microbes live in boiling water (90 C). Other pools are extremely acidic, yet microbes and bacteria thrive there

Life in extreme conditions 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 ft long)

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 radiation. They can go without food or water for more than 10 years and then revive.

Bacteria up to a mile underground: water seeps in, and bacteria generates energy from chemical reactions

(Less than 1 mm long)

Are there other places in our solar system that might harbor life?

We discussed the Goldilocks idea for Venus (too hot), Mars (too cold), Earth (just right)

Temperatures that allow liquid water may be very important

Could there have been life on Mars in the distant past?

1996: Martian meteorite found on earth, could it be possible fossil life from Mars? Current thinking is that this is not a fossil, but it raises interesting questions

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 iceTitan: 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 relatively close to Jupiter

NASA Galileo mission, launched 1989, reached Jupiter 1995, orbited with flybys of moons until 2003

Found the surface of Europa is covered in ice, long fractures – suggests liquid water underneath ( heated by strong tides from Jupiter)

Liquid water: raises possibility of primitive life? Next, an Aside on tides:

Aside on tides:Earth- moon: ocean tides caused by gravity ( force = mass, inverse distance)

Tides consume energy (friction): lead to tidal locking

Example of tidal locking: moon keeps one face to the earth all the time)

Surface of Europa, from the Galileo mission, showing “ice rafts”

A theoretical model of possible ocean on Europa. (Rick Greenberg, UA)

Scale: This image is 20 by 50 miles

NASA Cassini mission to Saturn:

Launched 1997, arrived 2004Cassini made multiple 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 still orbiting Saturn, sending back data

Saturn’s largest moon: TitanView of surface from Huygens probe, which parachuted to the surface

atmosphere

Surface:Surface from about 30 km

Titan: further exploration suggest lakes of liquid methane, ethane: a “water cycle” than involves no water!

While these are interesting 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 statistical estimate exercise:

how many left-handed, 8 year old boys are there is the US right now?

how many left-handed, 8 year old boys are there is the US right now?

1. Population of the US, P:

2. Fraction of males, Fm

3. Fraction of people who are left handed Fl

4. Fraction of population who are 8 years old F8

•Answer = P * Fm* Fl* F8

Scientific Notation: or handling big numbers

scientific notation: 1,000 = 103 = one thousand1,000,000 = 106 = one million1,000,000 = 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 Equation: statistical estimate of the number of intelligent, communicating civilizations in our galaxy

right now

1. Number of stars in our galaxy2. Fraction of stars that have planets around them3. Number of planets per star that are capable of supporting life (see

habitable zone)

4. Fraction of planets where life evolves5. Fraction of these planets where intelligent life evolves6. Fraction of intelligent life that communicates7. Fraction of a planet’s lifetime during which the civilizations

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 galactic orbit.Vc = velocity of sun around galactic centerr = distance from sun to galactic 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 fraction of stars that have planets?

Kepler Project: indicates that practically all sun-like stars have planets

Although Kepler looks at a very small fraction of the Milky Way galaxy, it should be representative of most

Is is appearing that the majority of planets are more earth-like than Jupiter-like

http://astro.unl.edu/naap/habitablezones/animations/stellarHabitableZone.html

• 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,

orbiting in a temperate environment. “

3. What number of planets are able to support life?

The other factors ( 4 through 7 ) are up to you:

Note that this ONLY addresses our galaxy: there are about as many galaxies in the known universe as there are stars in our galaxy!

Values you get?

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, citizen science program, using personal computers to help with data reduction, also support from Planetary Society (private group)

Small percent of time devoted to this search,

SETI Project: the Allen Telescope array

• Need for more telescope time: proposal to build up to 350 small radio telescopes,

• supported by Paul Allen (Microsoft 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 galactic plane for very powerful transmitters

What sort of signal is SETI looking for?

•The Arecebo telescope does not track the sky, so a exterrestrial signal will drift 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 information, it will be pulsed

•Since planets (like us) probably rotate, it may show a Doppler shift , 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?