Week 1 Continued How to Build a Habitable Planet Stars………

Week 1 continued How to Build a Habitable Planet Stars………. Origin of the Solar System, Earth and Moon, Earth differentiation into core, mantle and crust ………..atmosphere and hydrosphere Making a Habitable Planet

• The right kind of star and a rocky planet • A benign cosmological environment • Matter, temperature where liquid water stable, energy • And many more…………see WS Broecker, How to Build a Habitable Planet Astronomical Distance Scales Some Common Distance Units: •Light Year: the distance that light travels in one year (9.46 x 10^17 cm). •Parsec (pc): 3.26 light years (or 3.086 x 10^18 cm).; also kiloparsec (kpc) = 1000 parsecs and megaparsec (Mpc) = 1,000,000 parsecs. •Astronomical Unit (AU): the average separation of the earth and the sun (1.496 x 10^13 cm).

Some Representative Distances: •The Solar System is about 80 Astronomical Units in diameter. •The nearest star (other than the sun) is 4.3 light years away. •Our Galaxy (the Milky Way) is about 100,000 light years in diameter. •Diameter of local cluster of galaxies: about 1 Megaparsec. •Distance to M87 in the Virgo cluster: 50 million light years. •Distance to most distant object seen in the universe: about 18 billion light years (18 x 10^9 light years). A little about Galaxies!

•A remarkable deep space photograph made by the Hubble Space Telescope •Every visible object (except the one foreground star) is thought to be a galaxy. Image courtesy of NASA. Galaxy Geometries & The Milky Way •There are many geometries of galaxies including Images removed due to copyright restrictions. the spiral galaxy See http://hyperphysics.phy-astr.gsu.edu/hbase/astro/imgast/galaxo.gif. characteristic of our own Milky Way.

•Several hundred billion stars make up our galaxy •The sun is ~26 lt.y. from the center Spiral Galaxy NGC 6744

Image courtesy of NASA. Protostar Formation from Dark Nebulae

Cores of ca 1000 t=0 solar masses

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See http://abyss.uoregon.edu/~js/images/cloud_frag.gif

Clumps of ca 10-50 Dark Nebulae: Opaque solar masses and clumps or clouds of gas 0.1pasec dia and dust. Poorly defined outer boundaries (e.g., serpentine shapes). Large DN visible to naked eye t=10 m.y. as dark patches against the brighter background Image courtesy of NASA. Image courtesy of NASA. of the Milky Way. Image courtesyof NASA.

Protostar Formation from a dark nebula in the constellation Serpens

•Hubble Space Telescope image Image courtesy of NASA. Orion Nebula Candidate Protostars in the Orion Nebula

Images courtesy of NASA. Star Formation from Protostar

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See http://abyss.uoregon.edu/~js/images/protostar.gif Star Maintenance

•Gravity balances pressure (Hydrostatic Equilibrium) •Energy generated is radiated away (Thermal Equilibrium)

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See http://abyss.uoregon.edu/~js/images/thermal_equilibrium.gif

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See http://abyss.uoregon.edu/~js/images/hydrostatic_equilibrium.gif All objects emit energy in the shape of Planck's curve, where the amount and the peak energy vary only as the temperature of the body.

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See http://abyss.uoregon.edu/~js/images/planck_curve.gif Electromagnetic Spectrum •The Sun, a relatively small & cool star, emits primarily in the visible region of the electromagnetic spectrum. •Fainter & hotter objects emit energy at longer & shorter Visible Spectrum λ’s, respectively.

Image courtesy of the U.S. Geological Survey. Transparency of Atmosphere

However, Earth atmosphere is opaque to certain wavelengths

Image removed due to copyright restrictions. Graph showing that the Earth’s atmosphere is mostly opaque to all but visual light and radio waves; see http://abyss.uoregon.edu/~js/images/transparency.jpg Spectra of Elements •All elements produce a unique chemical fingerprint of “spectral lines” in the rainbow spectrum of light. •Spectra are obtained by spectroscope, which splits white light into its component colors.

Image removed due to copyright restrictions. Image removed due to copyright restrictions.

Figure showing a photographic spectrum, and a graph of its line See http://abyss.uoregon.edu/~js/images/kirchhoff.gif for intensity profile; see http://abyss.uoregon.edu/~js/images/a3combo.gif illustration of emission/absorption lines concept. for image. Doppler Effect Occurs when a light-emitting object is in motion with respect to the observer.

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Illustrations of blue shift and red shift; see http://abyss.uoregon.edu/~js/images/doppler.gif

•Motion toward observer: light is •Object receding from “compressed” (wavelength gets observer: λ increases, or gets smaller). Smaller λ = bluer light, “red shifted”. or “blue shifted”. Red Shift vs. Distance Relationship Example: If a shift toward red of hydrogen spectral •Spectral lines become shifted lines from a distant galaxy of against the rainbow background 10% is observed the galaxy when a distant object is in motion is speeding away from Earth (see Example). at 67 million mile per hour (0.1c). •All observed galaxies have red shifted spectra, hence all are receding from us. •More distant galaxies appear more Image removed due to copyright restrictions. red shifted than nearer ones, Illustration of red shift. consistent with expanding universe. •Hubble’s Law: red shift (recession speed) is proportional to distance. Surveying 101 A

Line of sight #1 B Angle A a s Rock e l i n Angle B Line of sight #2 e

•To determine distance to an object without B going to it: measure A-B and angles A & B A Astronomical Surveying

Line of sight #1 B Angle A a s e Star l i n Angle B Line of sight #2 e •Baseline = diam. of earth orbit (3x1013 cm) •Nearest star = 4x1018 cm B Works for ‘close’ objects; more distant ones can be surveyed by motion of our solar system through the galaxy Astronomical Distance Scales Some Common Distance Units: •Light Year: the distance that light travels in one year (9.46 x 10^17 cm). •Parsec (pc): 3.26 light years (or 3.086 x 10^18 cm).; also kiloparsec (kpc) = 1000 parsecs and megaparsec (Mpc) = 1,000,000 parsecs. •Astronomical Unit (AU): the average separation of the earth and the sun (1.496 x 10^13 cm).

Image removed due to copyright restrictions. Illustration of the local stellar neighborhood. Mass-Luminosity Relationship for Stars

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Graph of luminosity over mass for nearby stars; see http://abyss.uoregon.edu/~js/images/mass_luminosity.gif for image.

•A small sampling of stars near the sun. Actual

range of masses in our Galaxy is 0.08-100 Msun. Inverse Square Law

The brightness of an object varies inversely with the square of the distance from that object. Classification Image removed due to copyright restrictions. Graph of the relative strength of spectral lines versus stellar spectral class. of Stellar Ionized helium peaks around class O, neutral helium peaks around class B, hydrogen peaks around class A, ionized metals peaks around classes F and G, neutral metals peaks around class K, and molecules (TiO) slopes steeply upward Spectra past class M. See http://abyss.uoregon.edu/~js/images/stellar_lines.gif for image.

<--Increasing T,L Decreasing M,R-->

•Luminosity α to Mass type Mass Temp Radius Lum (Sun=1) ------•T inversely α to λ O 60.0 50,000 15.0 1,400,000 (Planck’s curve) B 18.0 28,000 7.0 20,000 •Spectral classification A 3.2 10,000 2.5 80 and color dictated almost F 1.7 7,400 1.3 6 solely by surface G 1.1 6,000 1.1 1.2 temperature (not K 0.8 4,900 0.9 0.4 chemical composition). M 0.3 3,000 0.4 0.04 ------Examples of Stars

Image courtesy of Wikipedia.

•Sun: middle-of-the-road G star.

•HD93129A a B star, is much Image removed due to copyright restrictions. See http://abyss.uoregon.edu/~js/images/HD93129A.jpg for larger, brighter and hotter. image depicting relative sizes of HD93129A and the Sun. Hertzsprung- Russell Diagram Image removed due to copyright restrictions.

See http://abyss.uoregon.edu/~js/images/pre_main_seq.gif

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See http://abyss.uoregon.edu/~js/images/hr_diagram_1.gif

•90% of all stars lie on main sequence

•Above Stars are from solar Neighborhood Stellar Evolution

Image removed due to copyright restrictions. Graph of main sequence for stars with stellar class included along x- axis; see http://abyss.uoregon.edu/~js/images/hr_diagram_3.gif Sun’s Evolution Onto the Main Sequence

Image removed due to copyright restrictions. See http://hyperphysics.phy-astr.gsu.edu/hbase/astro/imgast/sunev.gif.

•Where it will stay for ~10 b.y. (4.6 of which are past) until all hydrogen is exhausted… Sun’s Future Evolution Off the Main Sequence

Image removed due to copyright restrictions. See http://hyperphysics.phy-astr.gsu.edu/hbase/astro/imgast/sunfut.gif.

•In another ~5 b.y. the Sun will run out of hydrogen to burn •The subsequent collapse will generate sufficiently high T to allow fusion of heavier nuclei •Outward expansion of a cooler surface, sun becomes a Red Giant •After He exhausted and core fused to carbon, helium flash occurs. •Rapid contraction to White Dwarf, then ultimately, Black Dwarf. Red Giant Phase of Sun: t minus 5 b.y.… •For stars of less than 4 solar masses, hydrogen burn-up at the center triggers expansion to the red giant phase.

Image removed due to copyright restrictions. See http://hyperphysics.phy-astr.gsu.edu/hbase/astro/imgast/sunrg.gif.

White Dwarf Phase of Sun •When the triple-alpha process (fusion of He to Be, then C) in a red giant star is complete, those evolving from stars < 4 Msun do not have enough energy to ignite the carbon fusion process. •They collapse, moving down & left of the main sequence, to become white dwarfs. •Collapse is halted by the pressure arising from electron degeneracy (electrons forced into increasingly higher E levels as star contracts).

Image removed due to copyright restrictions. See http://hyperphysics.phy-astr.gsu.edu/hbase/astro/imgast/whdw.gif

(1 teaspoon of a white dwarf would weigh 5 tons. A white dwarf with solar mass would be about the size of the Earth.) End of a Star’s Life

•Stars < ~25 Msun evolve to white dwarfs after substantial mass loss. •Due to atomic structure limits, all white dwarfs must have mass less than the

Chandrasekhar limit (1.4 Ms). •If initial mass is > 1.4 Ms it is reduced to that value catastrophically during the planetary nebula phase when the envelope is blown off. •This can be seen occurring in the Cat's Eye Nebula:

Image courtesy of NASA. Supernovae: Death of massive stars > 25 Solar masses Image removed due to copyright restrictions.

See http://abyss.uoregon.edu/~js/images/sn_explosion.gif

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See http://abyss.uoregon.edu/~js/images/hr_diagram_3.gif Supernovae Images courtesy of NASA. •E release so immense that star outshines an entire galaxy for a few days.

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Illustration of supernova-induced star formation; see http://abyss.uoregon.edu/~js/images/star_propagation.jpg

Supernova 1991T in galaxy M51 •Supernova can be seen in nearby galaxies, ~ one every 100 years (at least http://abyss.uoregon.edu/~js/ast122/lectures/lec13.html one supernova should be observed if 100 galaxies are surveyed/yr). The Solar System and Earth Accretion & Differentiation Formation of the Solar System

• Sites and images Æ Maria Zuber Website 12.004 Introduction to Planetary Science http://web.mit.edu/12.004/www/sites.html

Text: Earth System History Steven M. Stanley, 1998 Other Readings: WS Broecker, How to Build a Habitable Planet 5 papers in Scientific American Oct 1994 Volume 271 from the big bang to pollution Weinberg, Peebles, Kirschner, Allegre and Orgel Delsemme, 1996, The origin of the atmosphere and of the oceans in Comets and the Origin and Evolution of Life (Eds Thomas, P.J., Chyba, C.F., McKay, C.P.) Chyba and Sagan, 1996, Comets as a source of Prebiotic Organic Molecules for the Early Earth in Comets and the Origin and Evolution of Life (Eds Thomas, P.J., Chyba, C.F., McKay, C.P.) • Rotating dust cloud (nebulae) Rotation causes flattening Gravity causes contraction Origin of Rotation increases Solar Material accumulates in center--protosun Compression increases T to 106 °C—fusion begins System: Great explosion Nebular • Origin of planets Gases condense Hypothesis Gravity causes them to coalesce into planetesimals Planetesimals coalesce & contract into planets • The planets Terrestrial or inner planets Mercury, Venus, Earth, Mars

loss of volatiles (H, He, H2O) by solar wind made of rock (O,Mg,Si,Fe) Jovian planets (4 of the 5 outer planets) Jupiter, Saturn, Neptune, Uranus mostly volatiles (H, He) Pluto

anomalous--rock w/ frozen H2O &CH4 Origin of Planetary System from Solar Nebula • Slowly rotating cloud of gas & dust • Gravitational contraction • High P=High T (PV=nRT) • Rotation rate increases (conserve angular momentum) • Rings of material condense to form planetesimals, then planets (Accretion) Figure by MIT OCW. The Solar System Anomalous Planet

Image courtesy of NASA. “Failed Planet” UB313 • When astronomers announced the discovery of UB313, the so-called tenth planet, a little more than a year ago, they had a hunch it might be bigger than Pluto because of its brightness. But despite several attempts to observe more closely the mysterious object orbiting the sun at a distance of more than 14 billion kilometers, accurate estimates of its size remained elusive. Now German astronomers working in Spain have determined that UB313 has a diameter of roughly 3,000 kilometers--roughly 700 kilometers larger than Pluto's • These calculations rely on several assumptions, however, such as UB313 lacking an atmosphere that would either reflect more light or trap more heat even though Pluto has such a covering. The astronomers estimate that the planet reflects roughly the same amount of light as Pluto, perhaps thanks to an icy methane surface. Their research appears in today's issue of Nature. The finding adds impetus to the debate surrounding what constitutes a planet. The International Astronomical Union is currently working on a definition based on minimum size so as to keep Pluto a planet, but this could open the possibility of even more planets in the outer reaches of the solar system. After all, UB313 is one of more than 1,000 objects discovered beyond the orbit of Neptune since 1992. In an accompanying commentary, Scott Sheppard of the Carnegie Institution of Washington suggests it might be time for a new term for such trans-Neptunian objects, much like "asteroid" was coined to refer to the many inner solar system objects discovered in the mid-19th century. If it is size that matters, however, it will be difficult to keep UB313 out of the exclusive planetary club. Says Bertoldi: "Since UB313 is decidedly larger than Pluto, it is now increasingly hard to justify calling Pluto a planet if UB313 is not also given this status." Asteroid 243 IDA

Image courtesy of NASA.

•Cratering indicates early origin •Chemical composition of meteorites collected on Earth indicate undifferentiated primordial material. Accretion of the Earth

Earth mostly accreted from rocky material in a large, viscous disc of dust around a young star (Laplace, 1796 and now supported by Hubble observations)

Earth accreted from planetesimals in the zone 0.8 to 1.3 au around the young sun where the temperature gradient (1500K to 900K) determined the chemical composition of condensing material and the ultimate composition of the bulk of the planet Coagulation of grains to 1m -1km sized objects x103 yrs; larger ‘embryos’ during ‘runaway growth 104-106 yrs formed objects lunar to martian mass Simulations predict an accretion time of roughly 50 million years for an Earth analogue to reach >90% of its final mass (review by Halliday et al. 2000) Chrondrites provide much of the evidence for planetary formation - ‘planets that never formed’. Chondrites = primitive objects, stony meteorites from the asteroid belt with elemental abundance ratios = those of the sun. Very heterogeneous rocks formed by accretion of grains (chondrules) with a variety of origins. Roughly ten times too much D/H to have delivered Earth’s water otherwise have solar elemental abundances Asteroids orbit roughly 2-4 Au ( between Mars and Jupiter) around the Sun but delivered slowly to the inner solar system. Different families identified by their spectral characteristics and the variable nature of meteorites. Some are undifferentiated – too small/cold to gravitationally separate into a core and mantle. Formation of the Earth by Accretion • Step 1: accretion of cm sized particles • Step 2: Physical Collision on km scale • Step 3: Gravitational accretion on 10-100 km scale • Step 4: Molten protoplanet from the heat of accretion

Image removed due to copyright restrictions. Please see images linked to from this page: http://zebu.uoregon.edu/ph121/l7.html. Accretion of the Earth: 2

Chrondrites provide much of the evidence for origins of nebula components and for planetary formation - ‘planets that never formed’.

Many chondrites have roughly ten times too much D/H (the deuterium excess) to have delivered Earth’s water otherwise have solar elemental abundances

Presence of ‘extinct isotopes’ eg Al26 now present as Mg26. Half-life of Al26 is low and all would be dissipated in 2 million years. Therefore Al26 must have been trapped in the solar nebula very early after it was formed in a supernova.

Chondrites contain a small proportion of ‘interstellar grains’ graphite, silicon carbide, fullerines with trapped noble gases Carbonaceous chondrites contain the most volatile elements and typically about 6% organic carbon. Thought to have delivered significant amounts of organic matter to the early Earth

Comets are nomadic bodies of ice, rock and organic and inorganic volatile compounds left over from the formation of our solar system. Comets come from the Kuiper belt located beyond Neptune, and from the Oort Cloud >200Au, which marks the outside edge of the solar system. Formation of the Earth by Accretion

•Tremendous heat generated in the final accretion process resulted in initially molten objects. •Any molten object of size greater than about 500 km has sufficient gravity to cause gravitational separation of light and heavy elements thus producing a differentiated body. •The accretion process is inefficient, there is lots of left over debris. •In the inner part of the solar system, leftover rocky debris cratered the surfaces of the newly formed planets (Heavy Bombardment, 4.6-3.8 Ga). •In the outer part of the solar system, the same 4 step process of accretion occurred but it was accretion of ices (cometisemals) instead of grains. http://zebu.uoregon.edu/ph121/l7.html The Sun & Planets to Scale

Image courtesy of NASA. NASA-JPL Accretion continues…

Chicxulub Crater, Gulf of Mexico •200 km crater •10-km impactor •65 Myr BP Image removed due to copyright restrictions. Photograph of Meteor Crater. •Extinction of 75% of all species!

Meteor (Barringer) Crater, Arizona Image removed due to copyright restrictions. Photograph of Chicxulub Crater. •1 km diam. Crater •40-m diam Fe-meteorite •50 kyr BP •300,000 Mton •15 km/s

http://www.gi.alaska.edu/remsense/features/impactcrater/imagexplain.htm Differentiation of the Earth:1

VM Goldschmidt 1922 published landmark paper ‘Differentiation of the Earth’ ‘Father of Geochemistry’ because of the realization that Earth has a chondritic (meteoritic) elemental composition. Surface rocks are not chemically representative of solar abundances therefore must be differentiated Proto-planet differentiated early into an iron-rich core surrounded by a metal sulfide-rich shell and a silicate-rich magma ocean Cooling of the magma caused segregation of dense silicate minerals – pyroxenes and olivines. Less dense minerals feldspars and quartz floated to surface to form crust. Less abundant elements segregate according to affinities for Fe = siderophile, sulfide = chalcophile and silicate = lithophile Differentiation of Earth

Figure by MIT OCW. •Driven by density differences •Occurred within ~100 Myr Differentiation of the Earth:2

R MA UPPE NTLE LITHOSPHERE ASTHENOSPHERE OLIVINE-RICH LOWER MANTL E MATERIAL

PEROVSKITE-RICH MATERIAL

CORE

4.4 BILLION YEARS AGO

4.2 BILLION YEARS AGO TO PRESENT

Figure by MIT OCW.

Allegre & Schneider, Sci. Am.(1994) Differentiation of the Earth:3

Proof of the differentiated planet comes from Slightly –flattened shape of the Earth Seismology – reflection and refraction of sound waves by materials of different densities and elasticities.

Continuous partial melting of mantle and the rising of less-dense components in ‘plumes’ , and the sinking or more dense ones drives tectonic cycles.

Tectonism essential for the continuity of life •Differentiation of Earth Differentiation Homogenous planetesimal of Earth, Earth heats up Continents,Differentiation of Earth, Accretion and compression (T~1000°C) Continents, Ocean & Radioactive decay (T~2000°C) OceanAtmosphere & Iron melts--migrates to center Atmosphere Frictional heating as iron migrates Light materials float--crust Intermediate materials remain--mantle

•Differentiation of Continents, Oceans, and Atmosphere Continental crust forms from differentiation of primal crust Oceans and atmosphere Two hypotheses internal: degassing of Earth’s interior (volcanic gases)

external: comet impacts add H2O CO2, and other gases Early atmosphere rich in H2, H2O, N2, CO2; deficient in O2 Early Earth History

Sun and accretionary disk formed (4.57) Some differentiated 0 asteroids (4.56) Earth accretion, core formation and Mars accretion degassing over first 100 million years. completed (4.54) Possible hot dense atmosphere. The Moon formed during Magma oceans. Little chance of life. mid to late stages of 100 Cooling of surface with Earth's accretion (4.51) loss of dense atmosphere. Loss of Earth's early atmosphere (4.5) 200 Earth's accretion, core formation and degassing essentially complete (4.47) Earliest granitic crust and liquid water. Earliest known Possibility of continents and primitive life. 300 zircon fragment (4.4) Bombardment of Earth could have repeatedly Upper age limit of most destroyed surface rocks, induced widespread known zircon grains (4.3) melting and vaporized the hydrosphere. Life may have developed on 400 more than one occasion.

500

Earliest surviving continental crust (4.0) Stable continents and oceans. 600 Earliest records thought to implicate primitive life. End of intense bombardment (3.9) 700

Figure by MIT OCW. Moon-Forming Impact Canup R & AspaugE:Eos Trans. AGU, 82(47), Fall Meet. Suppl., Abstract U51A-02, 2001 http://www.swri.edu/9what/releases/canupmoon.htm Hypothesis for lunar origin - Moon forms from debris ejected as a result of the collision of a roughly Mars-sized impactor with early Earth Geophysical simulations use a method known as smooth particle hydrodynamics, or SPH and can achieve resolutions sufficient to study the production of orbit-bound debris necessary to yield the Moon Off-center, low-velocity collisions yield material in bound orbit from which a satellite may then accumulate. Simulations must account for mass, angular momentum and compositions of the earth-Moon system. Must yield an Earth that retains an iron-rich core and a moon that is appropriately iron-depleted and the right density. SPH results suggest: The object had 10-12% of Earth’s mass Produces a satellite with <3% Fe by mass. Out of reach & unable to be captured subsequently Happened when Earth near its current ie final mass & near the very end of the accretion history

Earth from Space

•70% of surface covered with liquid water. •Is this necessary for the formation of life? •How unusual is the Blue Planet?

Image courtesy of NASA. The Habitable Zone

‘Goldilocks Metaphor’ 480ºC too hot no water

Venus atm. 90 bar

96% CO2 3% N2 Image courtesy of NASA. -60ºC too cold…..

Mars Atm.

Image courtesy of NASA. 95% CO2 2.7% N2 1.6% Ar no atmosphere …..and no life

Image courtesy of NASA. Atm of

78% N2 21% O2 1% Ar, CO2 and H20

15ºC + oceans

just

Image courtesy of NASA. right…... 10 water boils ) sun

3 Vl 1 sun

Stellar mass (M 1 Msun water freezes

0.1 1 10 100 Distance from star (AU) Figure by MIT OCW.

Must allow liquid water to exist! Habitable Zone of Continuously HZ Hz,t0 Solar

System Hz,t1 Venus

Sun Mars

Mercury

t1-t0 = 4.6 b.y.

Other Considerations Influencing HZ Caveat: We are relegated to only considering life as we know it & to considering physical conditions similar to Earth

• Greenhouse effect: Increases surface T

(e.g., Venus, at 0.72 AU, is within HZ, but Ts~745 K!)

• Lifetime of star: larger mass = shorter lifetime (must be long enough for evolution)

• UV radiation emission: larger mass = more UV (deleterious to life… as we know it)

• Habitable zone moves outward with time (star luminosity increases with age) Characteristics of the Habitable Zone

• Rocky planet and suitable star

• Clement intergalactic environment: low level of radiation and bombardment over sufficient time for evolution to take palce

• Temperature control to enable liquid water to be stable

• Sources of carbon and energy – CO2, organic matter – energy from chemistry of rocks + water – energy from the sun

• Mechanisms of renewal and recycling – Nutrients limited – Space = habitat limited (continents…)

• Mechanism = Tectonism. Is it that simple? The Drake Equation* Q: What is the possibility that life exists elsewhere?

A: N = Ng fp ne fl fi fc fL ~ 1,000 11 Ng=# of stars in our galaxy ~ 4 x 10 (good) fp=fraction of stars with planets ~ 0.1 (v. poor) ne=# of Earth-like planets per planetary system ~ 0.1 (poor) fl=fraction of habitable planets on which life evolves fi=probability that life will evolve to an intelligent state fc=probability that life will develop capacity to communicate over long distances fl fi fc ~ 1/300 (C. Sagan guess!) fL=fraction of a planet’s lifetime during which it supports a technological civilization ~ 1 x 10-4 (v. poor)

*An estimate of the # of intelligent civilizations in our galaxy with which we might one day establish radio communication. Recent detection of an extra-solar planet

Adapted from Konacki et al. by T. Brown, Nature, Vol. 421 (2003) HD209458b :http://www.space.com/scienceastronomy/shrinking_planet_030312.html

The planet, discovered in 1999 by a method that notes the gravitational wobble a planet induces on its star, is one of more than 100 worlds so far detected outside our solar system. Because the planet orbits so close to the star and in a favorable edge- on configuration, as viewed from Earth, astronomers have been able to study it in more detail than any other extrasolar planet. When HD209458b passes in front of its star, called HD209458, it blocks a bit of the starlight reaching Hubble. These so-called transit events, which occur every 3.5 days with this planet, allowed a different group of astronomers in 2001 to find sodium, marking the first detection ever made of an atmosphere of a planet around another star. Other hot Jupiters have been found in slightly tighter orbits, making a trip around their stars every 3 days. But only one has been found closer than that, even though closer- in worlds would be the easiest to detect. David Charbonneau of Caltech, who worked on the 2001 discovery of HD209458b's atmosphere, said the new study might suggest a reason why. "The implication is that planets initially located even closer to their stars would not survive long," Charbonneau writes in an analysis of the study for Nature. Charbonneau said the planet's mass loss may be a trickle or a flood -- the new data are not sharp enough to pin that down. He also said the planet's size and other characteristics had already indicated that it contained hydrogen, which is the most common element in the universe and the chief component of stars. Detecting Wobble

• Method relies on detection of a fluctuating solar spectrum via its Doppler Effect • Method detects only ‘close Jupiters’ ie huge planets with fat orbits. Most extra solar planets have been detected this way • The wobble can't tell us how massive the orbiting planet is because the Doppler shift only works if the object is moving toward us or away. It only detects only the star’s motion toward or away from us, not the full extent of the planet's pull. We know that the planet has offset the star at least as much as has been measured. The actual mass of the planet is thus a minimum, not an precise figure.

http://www.space.com/searchforlife/seti_wobble_method_010523.html “Feb. 3, 2004 — One of the best known planets beyond our solar system has surprised astronomers by revealing an oxygen, carbon and hydrogen- bearing atmosphere that's blowing away before our eyes. Image removed due to copyright restrictions. The exoplanet HD 209458, Illustration of Osiris's atmosphere being blown away as it orbits its sun. unofficially called Osiris, is 150 light-years away in the constellation Pegasus. It orbits its star at a dizzying rate of once every 3 1/2 days. It is a Jupiter- like gas giant that is far closer to its sun than Jupiter, and therefore is baked with 50,000 times more energy.”

http://dsc.discovery.com/news/briefs/20040202/planet.html# "It's a really, really hot planet," said space and planetary scientist Jonathan Fortney of the University of Arizona's Lunar and Planetary Laboratory (LPL). Fortney has done previous research that revealed sodium on the planet. Osiris is so hot that the 10,000-degree upper atmosphere has hydrogen atoms revved up to escape velocity — the speed that lets them escape the gravity of the planet and launch into space, said LPL's Gilda Ballester, co-author of a research paper announcing the discovery in the next issue of Astrophysical Journal Letters. Oxygen and carbon have also been detected in the hydrogen cloud around the planet, probably because the high-speed hydrogen atoms drag along the heavier atoms. "Like a river can carry silt if it moves faster," explained Ballester. The trick to identifying the elements was getting a good look at light from Osiris with an ultraviolet-detecting instrument aboard the Hubble Space Telescope. Ground based telescopes can't see the right wavelength of UV because they are filtered by the Earth's ozone layer. Because no telescope can actually image the planet itself, astronomers used the three-hour windows every 3 1/2 days when Osiris crosses in front of, and partially eclipses, its sun. During that "transit" time, the light of the star dims slightly and reveals the spectral signatures of Osiris, including the telltale ultraviolet signs of hot hydrogen, carbon and oxygen. "The planet is effectively evaporating very, very slowly," said Fortney of what the elements say about the planet. Although Osiris' sun is only slightly larger than our sun and about the same age, its solar system is dramatically different. Instead of orbiting hundred of millions of miles out, like Jupiter, Osiris is just four million miles from its sun, said Fortney. That's more than twenty times closer than Earth is to the sun.

http://dsc.discovery.com/news/briefs/20040202/planet.html# Origin of Earth’s Volatile Components Atmosphere, Oceans & Carbon •Arrived with the planetesimals, partly survived the accretion process and outgassed during volcanic activity (Hogbom 1894, Rubey 1951-5). Volcanic gases vary in composition; not primordial and may have been recycled many times. No record of the time and conclusive answers about this scenario (Turekian, 1972; Delsemme, 1997). •Arrived with comets during the late bombardment - late veneer hypothesis (Delsemme, 1997) •Arrived with one or more hydrated planetesimals from the outer asteroid belt (Morbidelli, 2001) •Arrived with comets and mixed with accreted water Arrived with comets and mixed with accreted water http://www.agu.org/cgi-bin/SFgate U51A-05 Origin of Earth's Volatiles: The Case for a Cometary Contribution : Owen, T C

D/H show comets could not have delivered all the Earth's water. 84Kr/132Xe and the isotopic composition of Xe show that chondrites did not deliver the atmospheric noble gases. The existence and extent of a cometary contribution to the Earth's oceans and atmosphere can be sought through studies of isotopic ratios and noble gas abundances. Because its atmosphere is so thin and it lacks plate tectonics, Mars provides a useful control on models for volatile delivery. Here we find evidence for a cometary-delivered hydrosphere decoupled from a lithosphere that contains xenon with solar isotope ratios. The Martian atmosphere reveals krypton and xenon relative abundances and isotope ratios remarkably similar to Earth's, despite obvious evidence for atmospheric escape. An external source seems necessary to satisfy both Martian and terrestrial data with the D/H result pointing toward comets. This result requires that Earth formed with its own water, to mix with the cometary component. The ratios of 15N/14N on Mars and Earth (in the atmosphere and rocks) are also consistent with cometary delivery of nitrogen in the form of N-compounds. Arrived with one or more hydrated planetesimals from the outer asteroid belt (Morbidelli, 2001) http://www.agu.org/cgi-bin/SFgateU51A-04 The Formation of a Water-Rich Earth Morbidelli, A The radial extent of the primordial population of planetary embryos I not known. In principle, a system of embryos originally within 2 AU from the Sun could form terrestrial planets on time-scales compatible with geochemical constraints (4). However, an even better agreement with the geochemical time-scales is achieved if one postulates that the formation of the embryos occurred also in the asteroid belt (5). This scenario has additional advantages: (i) the original presence of planetary embryos explains the presently observed properties of the asteroid belt (6); (ii) in ¾ of the cases a terrestrial planet accreted at least one embryo coming from the outer asteroid belt, which was presumably heavily hydrated, on the basis of meteorite analyses and modeling of the solar nebula. This could have brought to the Earth up to 10 times the present amount of water in the crust, with the correct isotopic composition (7). The amount of water carried to the Earth by small asteroids and comets is negligible with respect to that acquired through the accretion of an hydrated embryo, and it would not be enough to explain the current budget of water on Earth. Nevertheless this contribution may be important, because it occurred since the very beginning of the planet's formation. Selected references: (1) Wetherill and Stewart, 1989, Icarus 106, 190 (2) Weidenschilling et al., 1997, Icarus, 128, 429 (3) Wetherill, 1992, Icarus, 100, 307 (4) Chambers and Wetherill, 1998, Icarus 136, 304 (5) Agnor et al., 1999, Icarus, 142, 219 (6) Petit et al., 2001, Icarus, in press (7) Morbidelli et al., 2000, Meteoritics, 35, 1309 Arrived predominantly with comets – late veneer (Delsemme 1997) • Cratering record of the Moon, and Mars confirms massive bombardment at the tail of the main accretion – would have dissipated any volatiles • Modeling of cometary diffusion is consistent and predicts a subsiding flux of bolides • A 1% volatile fraction of Earth coming from comets explains the right proportions of siderphile elements present in the crust. They were not ‘scavenged’ by the core confirming that they must be from a later veneer. • D/H ratios ‘consistent with quenching’ of water-snow at 200°K from the nebular gas, stored in comets and then brought into the oceans • Improved knowledge of the chemical compositions of comets will help to constrain the hypotheses Composition of Comet Halley Volatiles (modeled)

78.5 % H2O2.6% N2 1.5% C2H4 0.1% H2S

4.0% H2CO 0.8% NH3 0.5% CH4 0.05% S2

4.5% HCO-OH 1.0% HCN 0.2% C3H2 0.05% CS2

1.5% CO 0.8% N2H4

0.4% C4H4N2

92% with O 5.6% with N 2.6% H/C 0.2% S Early Composition of the Atmosphere

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0 4.5 4 3 2 1 Time (Billion of years ago) Atmospheric composition, shown by the relative concentration of various gases, has been greatly influenced by life on the earth. The early atmosphere had fairly high concentrations of water and carbon dioxide and, some experts believe, methane, ammonia, and nitrogen. After the emergence of living organisms, the oxygen that is so vital to our survival became more plentiful. Today carbon dioxide, methane and water exists only in trace amounts in the atmosphere.

Figure by MIT OCW. Why the big deal with water? http//www.esa.int/rosetta

The countdown to Rosetta’s rendezvous in space began on 1 March 1997. At the end of February 2004, seven years and not a few headaches later, the European Space Agency (ESA) probe will at last be setting off on its journey to meet Comet Churyumov-Gerasimenko. The long-planned get-together will not however take place until the middle of 2014. A few months after arriving at the comet, Rosetta will release a small lander onto its surface. Then, for almost two years it will investigate Churyumov-Gerasimenko from close up.

Rosetta will be waved off on 26 February when it lifts off from the space centre in Kourou, French Guiana, aboard an Ariane 5 launcher. Shortly after the spacecraft’s release, its solar panels will be deployed and turned towards the Sun to build up the necessary power reserves. Its various systems and experiments will be gradually brought into operation and tested. Just three months into the mission the first active phase will be over, followed by final testing of the experiments in October 2004. Rosetta will then spend the following years flying a lonely path to the comet, passing by the Earth, Mars, the Earth and the Earth again. Why the big deal with water? http//www.esa.int/rosetta

The comet explorer carries ten scientific instruments. Their job is to draw out the secrets of the comet’s chemical and physical composition and reveal its magnetic and electrical properties. Using a specially designed camera, the lander will take pictures in the macro and micro ranges and send all the data thus acquired back to Earth, via Rosetta.

“This will be our first ever chance to be there, at first hand, so to speak, as a comet comes to life,” Schwehm goes on to explain. When Churyumov-Gerasimenko gets to within about 500 million kilometres of the Sun, the frozen gases that envelop it will evaporate and a trail of dust will be blown back over hundreds of thousands of kilometres. When illuminated by the Sun, this characteristic comet tail then becomes visible from Earth. In the course of the mission, the processes at work within the cometary nucleus will be studied and measured more precisely than has ever before been possible, for earlier probes simply flew past their targets. Characteristics of the Habitable Zone: known requirements of life? • Liquid water •Sources of carbon and energy •CO2, organic matter •energy from chemistry of rocks + water •energy from the sun •Mechanisms of renewal and recycling •Nutrients limited •Space = habitat limited •Mechanism = Tectonism. Is it that simple? Copernicus 1473-1543 Hypothesised Earth circularly orbited Sun c. 1543 slow to publish. German printer took liberty of adding unwlecome preface. Saw it on his deathbed

Tycho Brahe 1546-1601 Observed planet positions. Hired Kepler but was mean with the data and died before the results c. 1600

Johannes Kepler 1571-1630 Analysed Image removed due to copyright restrictions. Image of the cover of Galileo’s Daughter. Tycho’s data and developed Kelper’s laws and eliptical orbits c. 1610

Galileo Galilei 1546-1642 Built good telescopes, confirmed Kepler c. 1610 and wore the wrath of Rome c. 1623

Isaac Newton 1642-1727 Principia 1687 Water Elsewhere in the Solar System Ice - Rafts on Europa

Image courtesy of NASA. Water Elsewhere in Solar System CO2 + Water Ice on Mars http://photojournal.jpl.nasa.gov/

Image courtesy of NASA. Water Elsewhere in Solar System Flat topography of Mars Northern Hemisphere

http://photojournal.jpl.nasa.gov/ Image courtesy of NASA. Water Elsewhere in Solar System Evidence of recent water flow on Mars http://www.msss.com/mars_images/moc/june2000/age/index.html

Images courtesy of NASA. Water Elsewhere in Solar System Evidence of recent water flow on Mars http://www.msss.com/mars_images/moc/june2000/age/index.html Gullies seen on martian cliffs and crater walls in a small number of high- resolution images from the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) suggest that liquid water has seeped onto the surface in the geologically recent past. The gully landforms are usually found on slopes facing away from mid-day sunlight, and most occur between latitudes 30° and 70° in both martian hemispheres. The relationship to sunlight and latitude may indicate that ice plays a role in protecting the liquid water from evaporation until enough pressure builds for it to be released catastrophically down a slope. The relative freshness of these features might indicate that some of them are still active today--meaning that liquid water may presently exist in some areas at depths of less than 500 meters (1640 feet) beneath the surface of Mars. The evidence for recent water activity is described in a paper by MGS MOC scientists being published in the June 30, 2000, issue of Science. The gullies are rare landforms that are too small to have been detected by the cameras of the Mariner and Viking spacecraft that examined the planet prior to MGS. This picture (left), acquired by the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) in May 2000 shows numerous examples of martian gullies that all start—or head-- in a specific layer roughly a hundred meters beneath the surface of Mars. These features are located on the south- facing wall of a trough in the Gorgonum Chaos region, an area found to have many examples of gullies proposed to have formed by seepage and runoff of liquid water in recent martian times.

Images courtesy of NASA.