Transcript Jovian planets

G345U: Life in the
Universe - is an
introductory overview of
the field of astrobiology.
Quiz
Syllabus
Whati is astrobiology?
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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 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
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.
Solar System diagram. The planet sizes are to scale, the distances between them are not.
Credit: The International Astronomical Union / Martin Kornmesser
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 #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
Main asteroid belt and typical NEA orbit
Asteroid
locations:
a snapshot
Main belt
Trojan
Trojan
Asteroid-Moon size comparison
(first ten numbered asteroids)
Moon
1 Ceres
4 Vesta
2 Pallas
3 Juno
5
6
7
8
9 10 Hygiea
--Over 300,000 asteroids (as of 2006)
--Virtually all <100 km across, largest ~930 km across
Largest Asteroid – still < half the size of Pluto
1 Ceres
2005 HST images
diameter = 930 km
Prot = 9.1 hrs
albedo = 0.10
a = 2.8 AU
Spectral class = G
density = 2.12 g/cm3
• 25% of all asteroid mass
• Probably differentiated, with near-surface water ice
• May contain more water than Earth
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 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
(40%)
Ixion (25-50%)
(60%)
Mainly
dark
(albedo
< 30%)
(12-30%)
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
usually small,
but some are
“planet sized”!
Comet orbits: long & short period
comet type
approx. a (AU)
approx. e
short period
(P ~ 3-200 yrs)
2 - 100
0 - 0.98
long period
(P > 200 yrs)
> 100
0.99 - 1
Pluto:
a ~ 39 AU, e ~ 0.25
Comets are derived from the
Kuiper Belt and Oort Cloud
Oort Cloud:
distant spherical
shell
KB
Kuiper Belt:
disk extending
outwards from
Neptune / Pluto
(ESA)
Nucleus
of comet
Wild-2
Wild-2 jets:
sources in
day & night
hemispheres
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.