Life in the Universe

The Elements of Life Organic Chemistry –By definition, involves H,C,N,O Most common elements (produced by most stars) Well dispersed and available –Occurs even in interstellar space Many organic compounds found in ISM, comets, meteors (despite extremely harsh conditions) –Easily delivered to early Earth, or produced locally Biochemistry –Requires liquid water? –Arises naturally when basic conditions met? What is “life”? –System out of chemical equilibrium which extracts energy from its environment to maintain itself Energy source could be heat, light, chemical, other? –Reliably reproduces, with opportunity for evolution Able to store and decode information for this

Basic Chemistry of Life (here) Digestion C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O + E Glucose + Oxygen YIELDS Carbon Dioxide + Water + Energy Photosynthesis 6CO 2 + 6H 2 O + E  C 6 H 12 O 6 + 6O 2 Carbon Dioxide + Water + Energy YIELDS Glucose + Oxygen From H,C,N,O (plus some trace amounts of heavier elements like P and Fe) are built nucleic acids, proteins, carbohydrates, and lipids, which can do the chemistry needed for both metabolism and evolution.

Habitable Zones (liquid surface water) Because the star keeps getting brighter, the continuously habitable zone is smaller than the habitable zone at a given time.

Climate on the Earth The Sun is getting brighter, and was 30% fainter in the beginning. We’d be frozen now without greenhouse gases (and really frozen then). Somehow the greenhouse effect has been regulated to keep liquid water on the surface. In less than a billion years, it will be hard to stop a runaway greenhouse on Earth (like Venus).

The Atmospheres of the Terrestrial Planets

Studying Extrasolar Terrestrial Planets Even if we can just get a spectrum, we might be able to detect signs of basic life.

The Martian Desert

Evidence of Water Flows on Mars Water cannot be a liquid on Mars’ surface now, but billions of years ago it flowed (there may even have been seas).

Water Distribution on Mars Water is concentrated near the poles, but is fairly widespread. It is likely mostly in the form of sub-surface ice.

The Martian Meteorite This rock IS from Mars. Does it contains signs of life? Most don’t think so now, But it is intriguing…. Bacterial fossil from Earth

Europa Europa is an ice-covered rocky moon. This “orbital resonance” keeps both Io and Europa internally heated. The stresses are apparent in the huge surface cracks. There is apparently a deep ocean under the ice, with volcanoes at the bottom. Natural color

Titan

The “Flow of Life” Genetic analysis gives us a window into the distant past, and clues on how life developed. Most of the biomass on the Earth is still bacterial, and they are best at filling ecological niches. Extreme life is found in amazing places. There is some indication that life could have started at deep undersea volcanic hydrothermal vents.

Emergence of Life on the Earth GyrFormation and intense bombardment –surface is uninhabitable GyrSurface stabilizes, simple life starts –RNA, DNA; thermophilic progenitor (chemical energy) GyrAnerobic prokaryotes, stromatolite beds –single-celled, no nuclei; oldest fossils formed GyrPhotosynthesis invented, free oxygen –surface life; use of sunlight; oxygen crisis GyrAerobic bacteria, eukaryotes –exploit available oxygen (more energy), cell nucleus Gyrbacteria diversify –Keep changing the mix, experiment GyrSexual reproduction invented –Evolve, baby! Gyrcomplex organisms appear –All current body plans appear, land colonized

The Drake Equation How Likely is Radio Contact With Extraterrestrial Intelligences? N IC = R IC x L IC = R star x P planets x P habitability x P simple life x P complex life x P radio signals x L radio era R IC xL IC rate at which civilizations appear x their lifetime Astronomy R star rate at which stars are formed in the Galaxy P planets probability a star will have planets P habitability probability a planet will be suitable for life Biology P simple life probability bacteria will arise on a suitable planet P complex life probability bacteria will evolve into complex life Sociology P radio signals probability complex life will send out radio signals L radio era total duration during which radio is sent

Evaluating the Odds for Simple Life N SL = R SL x L SL = R star x P planets x P habitability x P simple life Defensible Estimates R star observed rate: 10 per year P planets observed discoveries: 0.2 (some systems are unsuitable, but our sensitivity is poor) P habitability extreme life:0.1 (life seems to be everywhere) P simple life rapidity of life on Earth0.1 N SL = L simple life /200 = tens of millions! Thus, many astronomers are willing to say that a reasonable conclusion is that the Galaxy is full of life…

Evaluating the Full Odds Optimistically N IC = R IC x L IC = R star x P planets x P habitability x P simple life x P complex life x P radio signals x L radio era Optimistic Estimates R star observed rate: 10 per year P planets observed discoveries: 0.5 P habitability extreme life:0.5 P simple life rapidity of life on Earth1.0 P complex life long time on Earth0.2 P radio signals who knows ? (E-M is common) 0.02 N IC = L radio era /100pick your favorite duration… So if L re is greater than a few hundred years, there’s probably somebody out there. L re needs to be a million years for them to be neighbors (meaning within 1000 ly). The Galaxy’s a big place, and its been around a long time!

SETI : the search for extraterrestrial intelligence Our only real hope of detecting ET (unless they come to us) is by listening to the radio –Radio travels at the speed of light, over the whole Galaxy –Radio is a low energy way to send a message –We already have the ability to send and receive across the Galaxy Where should we listen? –Not the currently known extrasolar systems! –Solar-type stars? Milky Way? How should we listen? –Frequencies that are relatively quiet. –How narrow-band?The “water hole”? What should we listen for? –A regular carrier pattern. Complexity. What are the odds we will hear something? –The Drake equation Orbital Chaos 70 Vir system

…and so, we are listening! Allen Array Rapid Prototype Array Arecibo 2006 (Puerto Rico)

Evaluating the Odds Pessimistically N IC = R IC x L IC = R star x P planets x P habitability x P simple life x P complex life x P radio signals x L radio era Pessimistic Estimate R star observed rate: 10 per year P planets observed discoveries: 0.1 (no terrestrials known) P habitability extreme life:0.01 (surface liquid water to start it) P simple life rapidity of Earth life0.1 (we got lucky) P complex life long time on Earth0.01 (looks tough) P radio signals who knows?0.001 (what good are radios?) N IC = L radio era /100 million duration doesn’t much matter… Pessimistic Conclusion: There’s nobody home (except for us!). Let’s be careful, live long, and prosper!

THE END!!