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)

DigestionC6H12O6 + 6O2 6CO2 + 6H2O + E

Glucose + Oxygen YIELDS Carbon Dioxide + Water + Energy

Photosynthesis6CO2 + 6H2O + E C6H12O6 + 6O2

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 EarthThe 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 MarsWater 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

EuropaEuropa 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

• 0.0-0.5 Gyr Formation and intense bombardment– surface is uninhabitable

• 0.5-1.0 Gyr Surface stabilizes, simple life starts– RNA, DNA; thermophilic progenitor (chemical energy)

• 1.0-2.0 Gyr Anerobic prokaryotes, stromatolite beds– single-celled, no nuclei; oldest fossils formed

• 2.0-2.5 Gyr Photosynthesis invented, free oxygen– surface life; use of sunlight; oxygen crisis

• 2.5-3.0 Gyr Aerobic bacteria, eukaryotes– exploit available oxygen (more energy), cell nucleus

• 3.0-3.5 Gyr bacteria diversify– Keep changing the mix, experiment

• 3.5-4.0 Gyr Sexual reproduction invented– Evolve, baby!

• 4.0-4.5 Gyr complex organisms appear– All current body plans appear, land colonized

The Drake Equation How Likely is Radio Contact With Extraterrestrial Intelligences? NIC = RIC x LIC = Rstar x Pplanets x Phabitability x

Psimple life x Pcomplex life x Pradio signals x Lradio era

 

RICxLIC rate at which civilizations appear x their lifetime 

AstronomyRstar rate at which stars are formed in the GalaxyPplanets probability a star will have planetsPhabitability probability a planet will be suitable for life 

BiologyPsimple life probability bacteria will arise on a suitable planetPcomplex life probability bacteria will evolve into complex life 

SociologyPradio signals probability complex life will send out radio signalsLradio era total duration during which radio is sent

Evaluating the Odds for Simple Life

NSL = RSL x LSL = Rstar x Pplanets x Phabitability x Psimple life

Defensible EstimatesRstar observed rate: 10 per year

Pplanets observed discoveries: 0.2 (some systems are unsuitable, but our sensitivity is poor)

Phabitability extreme life: 0.1(life seems to be everywhere)

Psimple life rapidity of life on Earth 0.1

NSL = Lsimple 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

NIC = RIC x LIC = Rstar x Pplanets x Phabitability xPsimple life x Pcomplex life x Pradio signals x Lradio era

 

Optimistic EstimatesRstar observed rate: 10 per yearPplanets observed discoveries: 0.5 Phabitability extreme life: 0.5Psimple life rapidity of life on Earth 1.0Pcomplex life long time on Earth 0.2Pradio signals who knows? (E-M is common) 0.02 NIC = Lradio era/100 pick your favorite duration…

So if Lre is greater than a few hundred years, there’s probably somebody out there. Lre needs to be a million years for them to be neighbors (meaning within 1000 ly). The Galaxy’s a big place, andits 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 Chaos70 Vir system

…and so, we are listening!

Allen Array

Rapid Prototype Array Arecibo

2006

(Puerto Rico)

Evaluating the Odds Pessimistically

NIC = RIC x LIC = Rstar x Pplanets x Phabitability xPsimple life x Pcomplex life x Pradio signals x Lradio era

 

Pessimistic EstimateRstar observed rate: 10 per yearPplanets observed discoveries: 0.1 (no terrestrials known)Phabitability extreme life: 0.01 (surface liquid water to

start it)Psimple life rapidity of Earth life 0.1 (we got lucky)Pcomplex life long time on Earth 0.01 (looks tough)Pradio signals who knows? 0.001 (what good are radios?) NIC = Lradio 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!!