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.