Astrobiology: Life on other planets

Astrobiology Searching for life on other planets Friday, February 13, 2009

The Drake equation can be used to organize our thoughts Friday, February 13, 2009

Fermi paradox Friday, February 13, 2009

Fermi paradox • Time for an intelligent species to colonize galaxy: 106 years Friday, February 13, 2009

Fermi paradox • Time for an intelligent species to colonize galaxy: 106 years • Age of the Galaxy: 1010 years Friday, February 13, 2009

Fermi paradox • Time for an intelligent species to colonize galaxy: 106 years • Age of the Galaxy: 1010 years • where are they? Friday, February 13, 2009

How many planets are there? Friday, February 13, 2009

We now have discovered many planets around other stars, but no Earth analogs (yet) Friday, February 13, 2009

We now have discovered many planets around other stars, but no Earth analogs (yet) nsing microle habitable? pulsar Friday, February 13, 2009

Future missions approved by NASA will probe ‘habitable zone’ Friday, February 13, 2009

Kepler Transit search (scheduled launch 2/2009) Friday, February 13, 2009

In a transit search, we see when a planet passes in front of its star Friday, February 13, 2009

Transit searches are a cheap way to hunt for planets Friday, February 13, 2009

USING PHOTOMETRY TO DETECT EARTH-SIZE PLANETS The relative change in brightness (ΔL/L) is equal to the relative areas • (Aplanet/Astar) Jupiter: Earth or Venus 1% area of the Sun (1/100) 0.01% area of the Sun (1/10,000) Small planets need ultra-precise photometry. Must be done with wide- ﬁeld CCD imager in space. Friday, February 13, 2009

What have we learned from planet searches so far? Friday, February 13, 2009

Only high metallicity stars have planets FISCHER & VALENTI Vol. 622 lity /Star tirety sical ance 0.3 × Solar 3 × Solar 03). In addition, a Fig. 5.—Same results as Fig. 4, but divided into 0.1 dex metallicity bins. The s been underway increasing trend in the fraction of stars with planets as a function of metallicity is 004). No planets well ﬁtted with a power law, yielding the probability that an FGK-type star has a gas giant planet: P( planet) ¼ 0:03½(NFe =NH )=(NFe =NH ) 2:0 . veys, suggesting nets with orbital ikely lower than) Friday, February 13, 2009

Stars with planets are young. The Sun may be one of the oldest stars with planets – 37 – s net pla rs ith sta rs w cal l lo Sta Al Friday, February 13, 2009

What planets support life? Friday, February 13, 2009

What is life? Friday, February 13, 2009

Life as we know it Friday, February 13, 2009

What planets support life? What kinds of planets can support life? What fraction of planets that can support life do support life? Friday, February 13, 2009

The Habitable Zone is the range of distances from a star which allow a planet to support life Friday, February 13, 2009

What are the minimal conditions for life? • How hot? • How radioactive? • How cold? • How poisonous? • How dry? • How much pressure? • How acid? • How barren? • How salty? Organisms that push these limits are called extremophiles Friday, February 13, 2009

Thermophiles thrive at 90ºC (190ºF) Friday, February 13, 2009

Endolithic life eat and breath rock two miles undeground Friday, February 13, 2009

Dry valleys of antarctica 3 inches annual precipitation -68ºC Dry 200 mph winds evaporate all moisture Friday, February 13, 2009

Cryptoendolithic ecosystem inside rocks Algae White lichen Black Lichen Friday, February 13, 2009

Bacteria living at bottoms of perpetually frozen lakes. Friday, February 13, 2009

Extreme life in Permafrost Friday, February 13, 2009

Atacama Desert dryest place on earth 2 mm decadal precipitation recent discoveries of life below 4 inches Friday, February 13, 2009

Lifeless desert in Oceans • Centers of oceans have very little life. • Plenty of liquid water • Plenty of sunlight energy • Missing some key chemicals – Phosphorus Friday, February 13, 2009

Lessons from terrestrial life • Life can exist with only a bare minimum of ingredients: – Liquid Water – Some energy source • Sunlight, Rocks, Geothermal energy – Basic chemical ingredients • Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus Friday, February 13, 2009

Old Habitable Zone Theory • If planet is too close to star, fries through runaway greenhouse effect • If planet is too far from star, freezes, can’t support life. Friday, February 13, 2009

New Habitable Zone Theory • Many other factors besides distance from the Sun help determine planetary climate – Greenhouse effect – Plate Tectonics – Impacts (Early Earth atmosphere stripped) – Tidal Heating (Io, Europa) • Liquid water can be found in a variety of unlikely environments – Europa, Callisto, Ganymede – Early Mars very wet, present Mars dry? Friday, February 13, 2009

How many habitable planets will actually be alive? • Basic ingredients to make life are common throughout the cosmos • Look at History of Life on Earth • Life began shortly after Earth cooled • Suggests that Life is easy to make. Friday, February 13, 2009

Basic ingredients of life Friday, February 13, 2009

Basic ingredients of life • Organic molecules detected in interstellar space. Friday, February 13, 2009

Basic ingredients of life • Organic molecules detected in interstellar space. • Water (Ice) detected throughout galaxy, solar system. Friday, February 13, 2009

Basic ingredients of life • Organic molecules detected in interstellar space. • Water (Ice) detected throughout galaxy, solar system. • The basic chemical ingredients of life are common throughout the galaxy. Friday, February 13, 2009

Organic Molecules in interstellar space • Amino Acids • Nucleic Acids • Soot Friday, February 13, 2009

Given the right ingredients, how easy is it to make life? 34 Friday, February 13, 2009

Friday, February 13, 2009

Earliest Life • Bands of Carbon in ancient rock Friday, February 13, 2009

Conclusion from oldest life Friday, February 13, 2009

Conclusion from oldest life • Earth was not habitable until 3.8 billion years ago. – Too many impacts melted surface. Friday, February 13, 2009

Conclusion from oldest life • Earth was not habitable until 3.8 billion years ago. – Too many impacts melted surface. • 3.8 billion years ago, many fewer impacts. – Earth became inhabitable. Friday, February 13, 2009

Conclusion from oldest life • Earth was not habitable until 3.8 billion years ago. – Too many impacts melted surface. • 3.8 billion years ago, many fewer impacts. – Earth became inhabitable. • Oldest life on Earth 3.8 billion years old. Friday, February 13, 2009

Conclusion from oldest life • Earth was not habitable until 3.8 billion years ago. – Too many impacts melted surface. • 3.8 billion years ago, many fewer impacts. – Earth became inhabitable. • Oldest life on Earth 3.8 billion years old. • Life formed on Earth as soon as Earth could support life. Friday, February 13, 2009

Conclusion from oldest life • Earth was not habitable until 3.8 billion years ago. – Too many impacts melted surface. • 3.8 billion years ago, many fewer impacts. – Earth became inhabitable. • Oldest life on Earth 3.8 billion years old. • Life formed on Earth as soon as Earth could support life. • Life is easy to form? Friday, February 13, 2009

Searching for life in the Solar System 38 Friday, February 13, 2009

led ce n Ca Friday, February 13, 2009

Detection of life around other stars ned tpo pos ly nite efi Ind Friday, February 13, 2009

Biomarkers in atmosphere Friday, February 13, 2009

Biomarkers in atmosphere • Earth’s atmosphere shows strong signals of two biogenic molecules – Oxygen • Produced by plants – Methane • Produced by Cows Friday, February 13, 2009

Biomarkers in atmosphere • Earth’s atmosphere shows strong signals of two biogenic molecules – Oxygen • Produced by plants – Methane • Produced by Cows • Normally, methane burns in Oxygen – Natural Gas Friday, February 13, 2009

Biomarkers in atmosphere • Earth’s atmosphere shows strong signals of two biogenic molecules – Oxygen • Produced by plants – Methane • Produced by Cows • Normally, methane burns in Oxygen – Natural Gas • Two can only exist in combination because both being produced by life. Friday, February 13, 2009

What planets support intelligent life? Friday, February 13, 2009

Simple life Friday, February 13, 2009

Complex Life Friday, February 13, 2009

Lessons from Extremophiles • Complex life on Earth restricted to narrow range of habitats. – Not in Antarctica, too cold, dry – Not inside rocks, nothing to eat, breath – Not inside geothermal vents, too hot – Not in clouds, too heavy – Not in driest deserts, too dry Friday, February 13, 2009

Formation of Oxygen Atmosphere • Life begins to saturate atmosphere with Oxygen • Oxygen kills off life • Oxygen combines with rock • Life comes back, makes more oxygen • Oxygen kills off life • Process continued for 800 million years. Friday, February 13, 2009

Lessons from formation of life • Complex multicellular life did not evolve until recently. – Cambrian Explosion 600 Mya. • Complex life could not have evolved without Oxygen atmosphere. • Complex life more fragile than simple life. • Complex life difficult to evolve. Friday, February 13, 2009

Lessons from Mars • Planetary climates can change • Complex life (if it ever existed) likely wiped out today. • Simple life could have survived. Friday, February 13, 2009

Answer to Fermi Paradox? • Sun may be among the ﬁrst stars to have planets • Life may be common • Complex life may be rare • Complex life may take a long time to form • We may be alone? Friday, February 13, 2009

Intelligent life • No information how • Search for Extraterrestrial common intelligent life is. Intelligence: SETI – Cannot be federally funded – Took most of history of by congressional mandate earth to evolve an earthworm. – Now part of NASA’s Astrobiology Institute • Definition of Intelligent life: – Just another means to Ability to operate radio search for life transmitters – Privately Funded SETI • Search for intelligent life institute by searching for radio transmission Friday, February 13, 2009

The End Friday, February 13, 2009

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Astrobiology: Life on other planets

by David Graff on Feb 13, 2009

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