G345U: Life in the Universe - is an introductory overview of the field of astrobiology. Quiz Syllabus Whati is astrobiology? robio-origins.jpg

ASTROBIOLOGY Volume 6, Number 5, 2006 © Mary Ann Liebert, Inc. Education Paper The Astrobiology Primer: An Outline of General Knowledge—Version 1, 2006

TABLE OF CONTENTS Introduction Stellar Formation and Evolution 741 1A. The Formation of Stars 742 1B. The Evolution of Stars 744 1C. The Death of Stars 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 Astrobiogeochemistry and the Origin of Life 765 3A. Life’s Basic Components 765 3B. Evolution of Complexity 768 3C. Definition of Life 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 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 Diversity of Life 793 6A. Biodiversity 793 6B. Redox Chemistry and Metabolic Diversity 797 6C. Life in Extreme Environments 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

We are actually having problems defining “planet”. Planet definition #1 The 9 classical planets, period. Too few? Planet definition #2 An 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 #3 Same as #2, but greater in size than Pluto (2320 km diameter). 10 planets (so far).

Terrestrial Planets Mercury Venus Earth Mars 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 & Jupiter Near-Earth asteroid (NEA): planet-crossing Trojan 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 & Jupiter Near-Earth asteroid (NEA): planet-crossing Trojan 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

Asteroid locations: a snapshot 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 56789

1 Ceres diameter = 930 km P rot = 9.1 hrs albedo = 0.10 a = 2.8 AU Spectral class = G density = 2.12 g/cm 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 2 nd 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 moons HST 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 & albedo variety Mainly dark (albedo < 30%) Ixion (25-50%) (12-30%) (60%) (40%)

Pluto: a Kuiper Belt object Kuiper Belt

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 normal planet-forming process, but didn’t grow as large as Jovian planets. Perhaps to make a Jovian planet you have to grow a sufficiently large ice embryo to have 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 a larger object; survivors of the planetary sweep-up process includes: short period comet long period comet Kuiper Belt comet Oort 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 a larger object; survivors of the planetary sweep-up process includes: short period comet long period comet Kuiper Belt comet Oort Cloud comet usually small, but some are “planet sized”!

Comet orbits: long & short period comet typeapprox. a (AU)approx. e short period (P ~ yrs) long period> (P > 200 yrs) Comet orbits: long & short period comet typeapprox. a (AU)approx. e short period (P ~ yrs) long period> (P > 200 yrs) Pluto: a ~ 39 AU, e ~ 0.25

Comets are derived from the Kuiper Belt and Oort Cloud

KB Oort Cloud: distant spherical shell Kuiper Belt: disk extending outwards from Neptune / Pluto

(ESA)

Wild-2 jets: sources in day & night hemispheres Nucleus of comet Wild-2

So when we look at our solar system, we see: A star Objects 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.