Transcript PPT - Lunar and Planetary Laboratory

Extraterrestrial life and … extrasolar planets
PTYS/ASTR 206
Life / Exo Planets
5/1/07
Announcements
• Final exam – Thursday, May 10 11AM-1PM
– Brief review today
• Pick up past assignments!
• Office Hours
– Jade: not in this week
– John: as usual
– Me: as usual
– Email for times other than office hours
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Life / Exo Planets
5/1/07
Have we Been Visited by Aliens ?
Check out: http://www.ufoevidence.org/photographs/photohome.asp
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A UFO panel convened to discuss all of the
current evidence:
The Sturrock Panel
• They concluded that the UFO
problem is not a simple one
– No simple, universal answer
– Whenever there are
unexplained observations,
there is the possibility that
scientists will learn something
new by studying those
observations.
– Example: “ball lightning”
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Visual Evidence
example: UFOs and Ball Lightning
• UFOs
– Not reported by scientists
– Scientists are skeptical
• Ball Lightning
– Often reported by scientists (and others
who are deemed credible and
believable)
– Never photographed ! (confirmed to be
authentic)
– Not produced in a laboratory and
theoretical models are dubious (but a lot
of effort has been put into studying this)
– A physiological effect ?
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Sprites observed over a thunderstorm in Kansas in August, 2000
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• Mission update #1
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Life on Mars ?
• The Viking Lander had a
biological experiment
package on board to search
for life
– If life is confirmed to exist
on Mars, this would be a
scientific discovery of
EPIC proportions!
– In fact, some reason that
this alone supports the
Humans-to-Mars initiative
• ALH48001
– was there life on Mars in
the past ?
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Labeled Release
Experiment:
“Give them water”
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Pyrolytic Release
Experiment:
“Give them sunlight”
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Gas Exchange
Experiment:
“Give them food”
Viking Results Summarized
• A key find came from the GCMS
experiment
– Mars has NO organic compounds
– The surface of Mars is sterile
• The consensus opinion is that Viking
found no evidence for life on Mars
• Better location?
– We know more about the
surface of Mars now, perhaps a
better site selection would help!
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The Story of ALH84001
• A “SNC meteorite” found in
1984 in Alan Hills Antarctica
• Softball-sized meteorite
weighing about 4 lbs.
• In a 1997 article in Science,
David McKay indicated the
meteorite showed evidence
of primitive bacterial life on
Mars
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• A separate class of meteorites.
– Igneous rocks crystallized from
molten magma in a way which
suggests they formed in a
planetary-sized body, not an
asteroid
– They show evidence of shock
heating, presumably as a result
of the impact which ejected them
into space.
– Gas bubbles trapped in one
meteorite, EETA79001, have a
composition which matches the
current Martian atmosphere
• Names after the first 3 places where
they were found (Shergotty, Nakhla,
Chassigny)
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SNC Meteorites
4.5 Billion years ago -- The original
igneous rock solidified within Mars
3.6 - 4 billion years ago -- the rock was
fractured. Water then permeated the
cracks, depositing carbonate minerals
and allowing primitive bacteria to live in
the fractures.
3.6 billion years ago -- the bacteria and
their by-products became fossilized in
the fractures.
16 million years ago -- a large meteorite
struck Mars, dislodging a large chunk
of this rock and ejecting it into space.
13,000 years ago -- the meteorite landed
in Antarctica, where it was discovered
in 1984
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ALH84001 timeline
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globules
The Story of
ALH84001
• Simple organic compounds were
found on the fracture surfaces
• Carbonate “globules”
– look like mineral alterations
caused by primitive bacteria on
Earth
– Concentric “rings” of different
composition
– Magnetite was very pure
• “Ovoids”
– may be fossilized remains of
bacteria
– Extremely small
• Smaller than even single cells
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– Not life as we know it
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ovoids
• Where do we stand on this ?
– The original authors still maintain that this is
evidence of life on Mars.
– Most scientists believe that the evidence can
be explained by non-biological processes
• Need additional evidence
• The future?
– A sample-return mission would be important to
resolve the issue of life on Mars
• Very expensive
• A multinational plan for 2005 was scrapped due to
the back-to-back failures of 1999.
– The earliest launch of the next sample-return
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Planets
mission
is 2014 Life / Exo
5/1/07
• Mission update #2
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Extrasolar Planets
• About 8 years ago,
astronomers began finding
extrasolar planets, or planets
orbiting other stars
– More than 200 have been
detected so far
• They are not actually seen,
instead, their effects on their
parent star are oberved
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Methods of detecting extrasolar planets
• Astrometry (changes in the star’s
location)
• Radial Velocity (changes in the
star’s velocity)
• Transit method (dimming caused
by a transiting planet)
• Other methods:
– Pulsar timing, gravitational
microlensing, circumstellar
disks
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Habitable zone
• a region of space where conditions are favorable for life as it
can be found on Earth (water can exist as a liquid)
• This distance is centered on
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The recent discovery of a new
extrasolar planet that is within the
habitable zone of its parent star
It may be earth like – but the
diameter (and hence the density) is
not known without modeling
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• Mission update #3
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Final Exam
• Format:
– 6 short answer questions (4 pts each)
– 38 multiple choice questions (2 pts each)
– Closed book, closed note, no electronic devices (including a
calculator!)
– Bring a #2 Pencil
– You will have 2 full hours to take the exam
• What will it cover?
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Mostly material discussed in the lectures (75%)
Reading (25 %)
75% of the exam will be from Chapters 14-17
25% from topics covered throughout the course
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• A brief review of these follows
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Final Exam
• What should you study?
– Go over lecture slides
– Go over questions at the beginning of each chapter
– Go over key ideas and review questions at the end of
each chapter
– Go over in-class activities, quizzes, and homework
(except for mathematical questions)
• The solutions are on the website
A practice exam is now posted on the website
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Final Exam: A brief review of
comprehensive material (25% of exam)
• Chapters 1-4 : Basic Astronomy
– The motion and position of objects in the sky
• Diurnal motion, retrograde motion
• Reason for seasons
– Moon phases
– Kepler orbits and gravity
• Chapter 5: The Nature of Light and Atoms
– Wien’s Law
– Stefan-Boltzman law
– The Electromagnetic Spectrum
– Kirchoff’s Laws (emission and absorption lines in
spectra)
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Final Exam: A brief review of
comprehensive material (25% of exam)
• Chapters 7 and 8: The layout, nature, origin, age, and
formation of the Solar System
– Basic solar-system properties
• Terrestrial planets and gas giants
• All planets orbit the Sun in the same direction and
in the same plane
• Density of the planets
– The Solar Nebula
– The nebular hypothesis of the formation of the solar
system
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Final Exam: A brief review of
comprehensive material (25% of exam)
• Basic Planetary processes
– Interiors and Surfaces
– Review the “rules of thumb” discussed in the textbook
• p. 156 (in box 7-2)
• p. 159
• p. 161
– Planetary Magnetic Fields
– Atmospheres
• Chapter 9: The Earth
– Plate tectonics
– Structure of the interior
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Planets
– Greenhouse
effect Life / Exo
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Final Exam: A brief review of
comprehensive material (25% of exam)
• Chapter 18: The Sun
– Basic Structure (interior and atmosphere)
• Radiative zone – NOT radioactive zone!
– Energy Source
• Sun-Earth connection
– Sunspots and the sunspot cycle
• Sunspots are dim against the Sun, but still very bright!
– What is a geomagnetic storm?
– What is a cosmic ray?
• Chapters 10 and 11: The Moon and Mercury
– Lots of craters – why?
– Basic surface geology (highlands, mare)
– No atmosphere – why ?
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Planets
– Synchronous
rotation (due
to tidal
forces)
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Final Exam: A brief review of
comprehensive material (25% of exam)
• Chapter 12: Venus
– Why does it exhibit phases ? And why is it so bright?
– Runaway greenhouse effect
• Chapter 13: Mars
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Why is it at opposition every 2 years (nearly) ?
Evidence for Water
Atmosphere
Basic geology (northern vs southern regions)
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Life / Exo Planets
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Final Exam:
A brief review of Chapters 14-17 (75% of exam)
• Chapters 14 : Jupiter and Saturn
– Orbits
– composition
– Rotation
• Both are rapid and exhibit “differential rotation”
– Oblateness (Saturn is the most oblate)
– Features of the upper atmosphere
• Belts, and Zones, Giant Red Spot (Jupiter)
– Interiors
– Magnetic Fields
• Jupiter – extremely strong
• Saturn – aligned with rotation axis
– Planetary Rings (formation, gaps, which planets have
them? Saturn’s rings, etc.)
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Life / Exo Planets
5/1/07
Final Exam:
A brief review of Chapters 14-17 (75% of exam)
• Chapter 15: Jupiter and Saturn’s Moons
– Galilean Satellites: A Solar system in
miniature
– Io, Europa, Ganymede, and Callisto
– Titan and Enceladus
– Tidal forces (tidal heating of the moons)
– Connection to the Jovian Magnetosphere
• Io torus
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Life / Exo Planets
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Final Exam:
A brief review of Chapters 14-17 (75% of exam)
• Chapter 16: The Outer Worlds
– Uranus and Neptune
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How were they discovered?
Why are they blue-green in color?
Uranus has an unusual tilt
Both have unusual magnetic fields
– Pluto
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Discovery
Orbit
Charon
Kuiper-belt objects
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Life / Exo Planets
5/1/07
Final Exam:
A brief review of Chapters 14-17 (75% of exam)
• Chapter 17: Asteroids/Comets/Meteorites
– Asteroid Belt
– Kuiper Belt
– Oort Cloud
– Kirkwood Gaps
– Trojan Asteroids
– Asteroids shapes and brightness
– “Rubble piles”
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Life / Exo Planets
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Final Exam:
A brief review of Chapters 14-17 (75% of exam)
• Chapter 17: Asteroids/Comets/Meteorites (cont.)
– Meteorites
• Stony, irons, stony-irons, carbonaceous chondrites
– Comets
• Basic structure
• Orbits
• Meteor showers
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Life / Exo Planets
5/1/07