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G345U: Life in the Universe - is an introductory overview of the field of astrobiology.
Quiz
Syllabus
Whati is astrobiology?
http://faculty.washington.edu/dcatling/img/Astrobio-origins.jpg
http://www.fredbortz.com/AstrobiologyLg.jpg
ASTROBIOLOGYVolume 6, Number 5, 2006© Mary Ann Liebert, Inc.Education Paper
The Astrobiology Primer: An Outline of GeneralKnowledge—Version 1, 2006
TABLE OF CONTENTS
Introduction 739
1. Stellar Formation and Evolution 741
1A. The Formation of Stars 742
1B. The Evolution of Stars 744
1C. The Death of Stars 746
2. Planetary Formation and Evolution 748
2A. Planet Formation and Dynamical Evolution 748
2B. Asteroids, Comets, and Impacts on Earth 752
2C. Introduction to Geology 755
2D. Early Earth Environments 756
2E. Global Climate Evolution 760
3. Astrobiogeochemistry and the Origin of Life 765
3A. Life’s Basic Components 765
3B. Evolution of Complexity 768
3C. Definition of Life 771
4. Evolution of Life Through Time 771
4A. Overview 772
4B. Evolutionary Dynamics 772
4C. Molecular Phylogenetics 774
4D. Rare Events in Evolution 776
4E. Chemical Fossils 777
4F. Paleontology 780
5. Planet Detection and Characterization 783
5A. Methods of Planet Detection 783
5B. Planet Habitability 786
5C. Exploration and Characterization of Mars 788
5D. Exploration and Characterization of Europa 791
6. Diversity of Life 793
6A. Biodiversity 793
6B. Redox Chemistry and Metabolic Diversity 797
6C. Life in Extreme Environments 799
7. Science in Space 804
7A. Space Biology 804
7B. Planetary Missions 807
7C. Planetary Protection 809
Most people think about UFOs and contact with alien civilizations when they hear “Life In The Universe” or “Astrobiology”
Main topics of interest:
Extraterrestrial intelligent life/civilizations (SETI, Fermi Paradox, Drake Equation).
Extraterrestrial life in any form (what is life and how did it form; what conditions does life need - habitable planets and extremeophiles; what about our solar system - Mars, Europa, Titan)
Are there other Earthlike planets?(Spectra, detecting extrasolar planets, planet formation models, stellar lifecycles, where do elements come from?)
Interdisciplinary science: astronomy, biology, chemistry, engineering, geology, physics
Solar System diagram. The planet sizes are to scale, the distances between them are not.Credit: The International Astronomical Union / Martin Kornmesser
We are going to start with a survey of our solar system for two reasons: 1) We use our own system as an input to all of our models; and 2) As you will see, we have trouble classifying objects in our own system, which will complicate our discussions of exoplanets.
Definitions:
Solar system: All of the material (planets, moons, comets, asteroids, etc.) that is gravitationally bound to our star (the sun, or Sol)
Star: A gaseous sphere that produces enough heat in its interior by nuclear fusion to withstand the force of gravity
Planet: From a Greek word meaning wanderer. Originally, the little points of light that moved through the constellations. Now, reasonably large (but not too large) objects that orbit the sun.
The solar system that I learned about in grade school consisted of 9 planets orbiting the sun in a plane with all of the planets going around the sun the same direction.
The inner solar system consisted of 4 terrestrial (Earth-like) planets; the outer solar system consisted of 4 Jovian (Jupiter-like) planets and Pluto. An asteroid belt separated the inner and outer solar systems, and there were comets somewhere past the planets of the outer solar system
http://www.astro.psu.edu/users/niel/astro1/slideshows/class43/slides-43.html
We are actually having problems defining “planet”.
Planet definition #1The 9 classical planets, period. Too few?
Planet definition #2An object in orbit around the sun that is sufficiently large that self-gravity shapes it into a spherical form. Includes: biggest asteroids, biggest KBOs. Too many?
Planet definition #3Same as #2, but greater in size than Pluto (2320 km diameter). 10 planets (so far).
Terrestrial Planets
MercuryVenusEarthMars
and then there is our Moon
Mercury and the Moon have no atmosphere and are “dead” worlds
Venus lacks water and is not a hospitable place to visit
We know there is life on Earth – Mars is the only other PLANET in the solar system on which there might be life (notice I said PLANET, not OBJECT).
Asteroids:Small bodies (worldlets?) separate the inner solar system from the outer solar system
Asteroids
asteroid-- rocky or metallic object in orbit around the sun
includes:Main Belt asteroid: between Mars & JupiterNear-Earth asteroid (NEA): planet-crossingTrojan asteroid: Jupiter’s orbit
origin:mostly material that never accreted into a
larger object; survivors of the planetary sweep-up process
Asteroids
asteroid-- rocky or metallic object in orbit around the sun
includes:Main Belt asteroid: between Mars & JupiterNear-Earth asteroid (NEA): planet-crossingTrojan asteroid: Jupiter’s orbit
origin:mostly material that never accreted into a
larger object; survivors of the planetary sweep-up process
Main asteroid belt and typical NEA orbit
Asteroidlocations:a snapshot
Trojan
Trojan
Main belt
Moon
1 Ceres
Asteroid-Moon size comparison(first ten numbered asteroids)
2 Pallas 4 Vesta
10 Hygiea3 Juno
--Over 300,000 asteroids (as of 2006)--Virtually all <100 km across, largest ~930 km across
5 6 7 8 9
1 Ceres
diameter = 930 kmProt = 9.1 hrsalbedo = 0.10a = 2.8 AUSpectral class = Gdensity = 2.12 g/cm32005 HST images
• 25% of all asteroid mass• Probably differentiated, with near-surface water ice• May contain more water than Earth
Largest Asteroid – still < half the size of Pluto
Jovian planets
Moons of Jupiter – Io and Europa are larger than Pluto, Callisto is only slightly smaller than Mercury, and Ganymede is larger than Mercury – three of these may have liquid water layers in their interiors
Titan
• bigger than Mercury• 2nd largest moon in solar system• only moon with a significant atmosphere• organic chemistry in atmosphere
Cassini / Aug. 1, 2007
What about Pluto???
Pluto’s orbit brings it closer to the sun than Neptune;It is in a 3:2 resonance with Neptune(Neptune revolves 3 times for every 2 revolutions of Pluto)
Pluto has at least 3 moonsHST image
A Planet and its moon? A binary planet? Something else?
Kuiper Belt– region of space beyond Neptune that is populated by larger objects (KBOs) and is a source
of short period (<200 yr) comets
Classical Kuiper Belt
Size &albedovariety
Mainlydark(albedo< 30%)
Ixion (25-50%)
(12-30%)
(60%)
(40%)
Pluto: a Kuiper Belt object
KuiperBelt
Typical orbital features of classical KBOs:
1. Relatively low inclination orbits (<30 degrees)2. Prograde revolution around sun, like other planets
Hypothesis:
KBOs formed as part of normalplanet-forming process, but didn’tgrow as large as Jovian planets.
Perhaps to make a Jovian planet you have to grow a sufficiently large ice embryo tohave gas collapse onto the embryo.
Scattered KBOs: orbits more eccentric,often more inclined than other KBOs
Sedna:a scattered KBO,or something else?
Comets
comet-- icy object in orbit around the sun;shows coma (gas cloud) when sufficiently close to sun
origin: icy material that never accreted into alarger object; survivors of the planetarysweep-up process
includes:short period cometlong period cometKuiper Belt cometOort Cloud comet
Comets
comet-- icy object in orbit around the sun;shows coma (gas cloud) when sufficiently close to sun
origin: icy material that never accreted into alarger object; survivors of the planetarysweep-up process
includes:short period cometlong period cometKuiper Belt cometOort Cloud comet
usually small,but some are“planet sized”!
Comet orbits: long & short period
comet type approx. a (AU) approx. e
short period 2 - 100 0 - 0.98(P ~ 3-200 yrs)
long period > 100 0.99 - 1(P > 200 yrs)
Comet orbits: long & short period
comet type approx. a (AU) approx. e
short period 2 - 100 0 - 0.98(P ~ 3-200 yrs)
long period > 100 0.99 - 1(P > 200 yrs)
Pluto:a ~ 39 AU, e ~ 0.25
Comets are derived from theKuiper Belt and Oort Cloud
KB
Oort Cloud:distant sphericalshell
Kuiper Belt:disk extendingoutwards fromNeptune / Pluto
(ESA)
Wild-2 jets:sources inday & nighthemispheres
Nucleusof cometWild-2
So when we look at our solar system, we see:A starObjects made of rock and metal (terrestrial planets,
some moons, asteroids)Very large objects made mostly of gas/fluid (Jovian
planets)Objects made of rocky material plus ices (Pluto,
KBOs, some moons, comets
Among the things we want to explore this term is WHY our solar system looks like this – what we might expect other planetary systems to look like, and what conditions we might need or have on any of these objects for life to originate, exist, or evolve.