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Astrobiology – “Life in the Universe” Jason T. Olona Sandia High School

Astrobiology –“Life in the Universe” - physics.unm.eduphysics.unm.edu/Courses/McFadden/lectures/24_Astrobiology.pdf · special about our place in the universe. If life has developed

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• Astrobiology – “Life in the Universe”

Jason T. Olona – Sandia High School

• Astrobiology is a field of science that gets a lot of laughs…

Astrobiology: branch of science

concerned with the study of the origin of life

on Earth and the possible variety of life

elsewhere.

(OR)

Astrobiology: Study of the origins,

evolution, distribution, and future of life in

the universe.

• Synonymous with “exobiology,”

“cosmobiology,” and “bioastronomy.”

• BIG QUESTION:

• Our study of astronomy has taught us that we

have always been wrong in the past

whenever we have claimed that earth is

somehow unique…

• Center of the Solar system? Center of the

Universe? Sun is a special star? Planets are

special? Life is special?

• Copernican Principle: there is nothing

special about our place in the universe. If life

has developed here, why not elsewhere?

• To answer this question, we have to ask ourselves…

What is life?

- Reproduction, growth, energy utilization, (metabolism),

response to stimuli, evolutionary adaptation, ordered structure

of cells, heritable blueprint (DNA).

- Problem? Are we defining life on earth, or life in the universe?

• What is life?

• Life on Earth based on

organic molecules (Carbon)

• True question – is organic

biochemistry as likely or

unlikely in the universe at

large?

Behold!

The great

replicator

molecules!

• Life as we know it is based on

amino acids.

• SPONCH (CHNOPS)

– rare or common in universe?

• Life also needs ENERGY!

Could life form from other things? SURE?

Carbon based life = us. Silicon based life? Maybe…

Is water necessary? What about just a liquid?

Hypothetical solvents –

ammonia, sulfuric acids,

formamide, hydrocarbons, and (at

temperatures much lower than

Earth's) liquid nitrogen, or

hydrogen

• Origin of life on earth:

2 major theories

1) Life started here on Earth

2) Panspermia: Life (or the molecules

that are necessary for life) came

from somewhere else.

Comets? Mars?

• Early Earth – Hydrogen, ammonia,

methane, and water vapor.

• Primordial soup – take elements,

add energy, make new stuff!

• Urey-Miller experiment

Stanley Miller and Harold Urey (1930) Added water, methane, ammonia, and hydrogen to mimic early Earth atmosphere.

Result was organic molecules – amino acids!

- None of these experiments have

created DNA, rather they have showed

that biological molecules can be created

by non-biological means.

• Origin of life –• Inorganic molecules to organic molecules (4.5 billion years ago)

• First DNA and RNA (4.5-4.0 billion years ago)

• First cells – prokaryotes “LIFE” (4 billion years ago)

• Cells – eukaryotes (2 billion years ago)

• Multicellular life – (1 billion years ago)

• First land animals (500 million years ago)

Why do we assume extraterrestrial life exists?

1. Because life on Earth depends on just a few basic molecules

2. Because the elements that make up these molecules are

common to all stars

3. If physics is the same everywhere(!), given enough time, life

must have originated elsewhere in the cosmos.

Assumptions of Mediocrity

What would life on other planets look like?

What would life on other planets look like?

• Study extremophiles

• Extremophiles –

• Thermophiles – heat tolerant up to 122 C

• Psychrophiles – cold tolerant down to -25 C

• Acidophiles – pH values near 0

• Alkaliphiles – pH levels of 13 (bleach)

• Halophile – 10 times saltier than the ocean

• Barophile – 1000 atmospheric pressure

• Xerophile – little water

• Radiation – Deinococcus radiodurans

(1000x radiation we could withstand)

• Vacuum of Space – Tardigrades!

• So… what do we look for?

• Habitable Zone – water in liquid form. Distance from star.

• Biomarker: evidence of the presence of life, especially a global

indication of life on a planet that could be detected remotely

(unusual atmospheric composition).

• Ex: Photosynthesis changed earth’s atmosphere to 20% oxygen.

Should look for planets earth sized or gas presence that is difficult to

explain without life.

-Gases that may be signs of life - Nitrous oxide, methane, and oxygen

• Biomarker: evidence of the presence of life, detected remotely

(unusual atmospheric composition).

• Ex: Photosynthesis changed earth’s atmosphere to 20% oxygen.

Should look for planets earth sized or gas presence that is difficult to explain without life.

-Gases that may be signs of life - Nitrous oxide, methane, with oxygen

• “Life is the hypothesis of last resort” - Carl Sagan

• "When you hear hoofbeats, think of horses not zebras“

(we must exhaust all other explanations for what we are seeing before

we claim to have found evidence for life on other worlds).

- Possibilities in our Solar System – Mars? Europa? Enceladus? Titan?

• So… If Copernican principle is correct, biology could be common.

Why not intelligent life?

Fermi Paradox: if life and

intelligence are common, why

haven’t we found them?

Or they found us?

• Possible answers: maybe life is common but intelligence isn’t?

Maybe there hasn’t been enough time? Maybe advanced

species make it a practice to not interfere? Interstellar travel is

HARD and EXPENSIVE– extremely slow and energetically

expensive.

• SETI – Search for Extra Terrestrial

Intelligence

• If you want to bridge interstellar

distances, use EM spectrum!

• Talk is cheap! Travels at speed of light

and low energy cost.

• Earth is already on the air – AM radio

broadcasts since 1920s

• TV since 1950s

• What are we looking for?

• Problem: signals need to be from intelligent sources, rather

than naturally occurring.

• Narrow “bandwidth, pulsed signals, very little frequency “drift”

• So far, no detections. But the search continues!

• Aracibo message:

• Other messages: Pioneer 10 and 11 plaque & Voyager Record

Let’s Consider the Chances…

• How old is the universe?

• Stars in Milky Way?

• Like our Sun?

• How many galaxies?

• How many exoplanets?

• Like Earth?

13.8 Billion years old.

Conservative 250 Billion

Conservative 100 Billion in Milky Way

Conservative 200 Billion

Confirmed 4,000 in Milky Way

About 50 confirmed in Milky Way

Our chances of finding life in the universe is

directly proportional to how long we look

(aka how long our civilization lasts)...

• Drake Equation –

• goal is to estimate N = number of civilizations in our galaxy.

• N = R* Fp ne Fl Fi Fc LEach letter stands for a particular variable.

N = R* Fp ne Fl Fi Fc L

- R*= rate at which stars like out sun form – about 10 every year

- Fp = fraction of these stars with planets- ne = The number of planets per solar system that can incubate life- Fl = fraction of habitable planets that actually develop life.- Fi = planets that develop intelligent life - Fc = probability that intelligent societies that invent technology- L =lifetime of societies that use technology

If N = 1… just us?

Carl Sagan’s guess, N = a few million

Drake = 10,000 or conservative 500

www.seti.com to tinker with equation.

• What is the problem with the Drake equation?

• We only have one data point – Earth

So is this equation a little biased? It has to be! We can only

make assumptions based on things we know.