Transcript PHYS_3380_120715_bw - The University of Texas at Dallas

The final is Dec 14 at 2:00 PM
I will not be there as I have a meeting in San Francisco. Xu Liu will
proctor the exam. I will be available by phone if there are any
questions he cannot answer.
It will be 40% comprehensive and 60% what has been covered since
the last exam
You will be allowed two 8 ½ x 11 sheets of notes (both sides)
Your projects are due at the final.
Your grades will be available by Dec 21. You may email me or come
by my office in WSTC (call me or email me first to make sure I will be
there) if you want to know your grade on your final
I will place the rest of the homework solutions on line Wednesday.
PHYS 3380 - Astronomy
The Search for Extraterrestrial Life
PHYS 3380 - Astronomy
Earth-like worlds in a telescope like that on the proposed (and cancelled_
Terrestrial Planet Finder would still only appear as a single pixel of light.
• But looking at the spectra we might see the "fingerprints" of life and
learn about the chemistry of the planet's atmosphere.
Venus and Mars show the mark
of a carbon dioxide-rich
atmosphere, but only Earth's
spectrum has strong ozone and
water vapor fingerprints as well.
Spectral fingerprints of several important
chemicals for astrobiology
PHYS 3380 - Astronomy
Oxygen and its tag-along cousin ozone top the list of target molecules.
Without life, oxygen should be rare on rocky worlds.
A small amount of it can be created without life by ultraviolet radiation
that splits water vapor into hydrogen and oxygen. But that oxygen would
be readily consumed by rocks and minerals on the planet's surface in
the "oxidizing" reactions that produce, for example, rust. Volcanic gases
also react with oxygen and remove it from the atmosphere.
Oxygen gas is a good indicator of
life. But oxygen has been
abundant on Earth only since the
advent of photosynthesis -probably a billion years or more
after life began. To have the
greatest chance of spotting
extraterrestrial life,
astrobiologists must consider
how life looked on the young
Earth, too, when the atmosphere
was different.
PHYS 3380 - Astronomy
Life in the Solar System
PHYS 3380 - Astronomy
Life on Mars?
Mars is the only planet on which we have searched for life
• Early Mars may have been similar to early Earth
• Conclusive evidence that free-flowing water existed on Mars at one
time and actually exists at periods even today.
• Has all the chemical ingredients necessary for life as well as energy
from sunlight and now dormant volcanoes
• CO2 atmosphere
• May have significant amounts of subsurface ice - residual volcanic
heat may create pockets of liquid water where life could exist
• Microbacteria developed in labs can survive simulated Martian
conditions
PHYS 3380 - Astronomy
Viking Landers
Viking 1 and Viking 2 landed on Mars in 1976 - specific mission to look
for life. Equipped with robotic arms to scoop up soil samples and
deposit them in a closed container for treatment. Arms pushed aside
rocks to get at shaded soil less likely to have been sterilized by UV
light.
PHYS 3380 - Astronomy
Viking Life Detection Experiments on Mars
Living organisms alter their environment they breathe, eat, grow, and produce waste
Three experiments were designed to detect signs of living organisms by
treating soil samples in a closed environment (a container):
PHYS 3380 - Astronomy
Viking Life Detection Experiments on Mars
Gas exchange • Looked for changes in the atmosphere caused by metabolism of
organisms in the soil.
• Soil sample fed nutrient in a carbon dioxide (CO2) atmosphere.
• Organisms eat nutrients and release gases like CO2, methane,
oxygen and hydrogen into the container.
• Some gases were found but were thought to be due to chemical
reactions between the nutrient water and the soil.
PHYS 3380 - Astronomy
Viking Life Detection Experiments on Mars
Labeled release • Looked for CO2 breathed into the atmosphere
• Soil sample fed radioactive nutrient
• Organisms would release radioactive CO2 into the container
• Some gases were found but were thought to be due to the
chemical reactions between the nutrient and the soil
PHYS 3380 - Astronomy
Viking Life Detection Experiments on Mars
Pyrolytic release •Looked for radioactive carbon in soil sample
•Soil sample in radioactive CO2 atmosphere illuminated by ultraviolet
light to simulate sunlight
•Soil sample then heated to 650°C to decompose any growth
material in the soil
•Soil contained some radioactive carbon - did not represent life
Conclusion:
Some positive results found in each experiment. However, not
sufficient to confirm life as we know it
Explanation - unusual chemical activity
PHYS 3380 - Astronomy
Fossil Life in Meteorites
Possible fossil life found in meteorite discovered in Antarctica - hotly debated Meteorite came from Mars - air trapped in rock matches known Martian
atmosphere
• Age of meteorite 4.5 billion years - solidified shortly after Mars formed resided on Mars throughout period when Mars may have been warmer and
wetter
• Ejected from Mars 16 million years ago by large meteor impact
• Landed on Earth 13,000 years ago in Antartica
• Well preserved: not exposed to water erosion or industrial contaminants
PHYS 3380 - Astronomy
• While on Mars, meteorite was infiltrated by water - carbonate mineral
globules formed in water
• About 3.6 billion years old - when Mars was warmer and liquid water
may have existed - older than impact (asteroid?) that launched meteorite
into space
• Oxygen and carbon in globules contain isotopes characteristic of Mars
• Showed presence of polycyclic aromatic hydrocarbons (PAM) unlike any
on earth - associated with life
• Iron rich materials characteristic of fossil remains
PHYS 3380 - Astronomy
Pictures of meteorite taken with
electron microscope reveal
shapes that look much like
nanobacteria in existence on
Earth - fossils of microscopic life
on Mars? Hotly contested - other
scientists claim they are mineral
formations.
PHYS 3380 - Astronomy
Carbonate globules are the key to biogenic activity on Mars
• Globules formed in fractures of rock in liquid water
• Globules are younger than the rock
• Globular features resemble earth microorganisms, earth biogenic
carbonate structures and microfossils
•Globules contain PAH's
CONCLUSION:
Alternative explanations exist for each globular phenomenon
taken individually
Collectively, they are evidence for primitive life on Mars
NASA’s Mars Exploration Strategy: Follow the Water
Why is water on Mars important?
•
Geologic history - explanations for observed phenomena
•
Climate evolution - was Mars warm and wet?
•
Resources for future human exploration
In order for life, as we know it, to exist, water must be present.
Therefore, the finding of water on Mars is a precursor to finding life,
past or present on Mars.
PHYS 3380 - Astronomy
Ancient Water on Mars
Surface Water Ice
Frost at the Viking 2 landing site.
Image Credit: NASA/JPL
Northern residual polar cap as seen by
the Mars Orbiter Camera (MOC)
Phoenix
Phoenix Spacecraft:
Lander with robotic arm and scoop to dig trenches in the surface
- to look for water
- determine the mineralogy
- search for hydrocarbons
- assess potential habitability
Launched August 4, 2007.
Arrived May 25, 2008.
Phoenix lander on Mars
Picture taken by Mars Orbiting Spacecraft
Mars orbiting spacecraft, Odyssey, detected abundant water ice in the top
meter of Martian surface poleward of +/- 60°.
Landed in the Martian Arctic at approximately 68 degrees
N latitude, 233 degrees E longitude
(Earth equivalent: NW Territories, Canada)
Phoenix explored the farthest northern region of any Mars
mission to date.
UTD on Mars:
TEGA, Thermal and Evolved Gas Analyzer
TEGA is a combination of T - Thermal Analyzer - 8 high-temperature ovens - University of
Arizona
EGA - Mass spectrometer – University of Texas at Dallas
Samples of martian soil and regolith dug by the robotic arm are
- deposited in each of the 8 ovens.
- heated up to 1000 degrees C (1800 degees F)
- evolved gases analyzed by the UTD mass spectrometer.
Evolved Gas Analyzer
UT Dallas experiment:
Magnetic sector single focusing mass spectrometer.
1. Samples evolved gases from ovens during heating
cycles.
Measured relative abundances of evolved gases of
principal constituents.
2. Sampled atmosphere through constricted flow tube.
Measures relative abundances of gasses in the
martian atmosphere.
Mars surface covered with tiny rocks and pebbles and
displaying polygon shaped formations.
Polygons 1 to 2 meters across.
Photo taken with Surface Stereo Imager.
Polygon formation results from
seasonal expansion and
contraction of ground/ice
mixture as temperatures
change.
Exhibit central mounds and
perimeter troughs.
Troughs come from cracks from
that are filled with dirt and small
rocks.
Troughs are 1 cm to 10s of
centimeters deep.
Similar features seen in earth’s
permafrost arctic regions.
Robotic Arm: Rasping the Ice
Qui ckT ime ™ and a
MPEG-4 Vi d eo de comp re ssor
are ne ed ed to see thi s p i ctu re .
Left digging site called Humpty dumpty.
Right digging site called Wonderland.
Martian terrain looking west.
Robotic arm with scoop and robotic arm camera.
Surface material in scoop.
Solar cell panel
Exposing Water Ice
Trenches dug on Sol 17 named Dodo (left) and
Goldilocks (right)
Baby Bear taken from Goldilocks, delivered to TEGA
oven 4
Soils dumped on oven 4 exterior surface did not pass
through screen into oven.
Required vibrating screen for 6 sols for soil to drop into
oven.
Soils dried out. No water detected in soil sample.
How did we discover water on Mars?
Robotic arm scooped a sample from the bottom of a trench,
2 inches below the surface,
Deposited the sample in one of the TEGA ovens.
How did we discover water on
Mars?
Sol 113, Sept. 18 False Color Image of Snow
White trench.
Bright material near and below the four-byfour set of rasp holes in the upper half of the
image is water-ice exposed by rasping and
scraping in the trench earlier in the morning.
The back-hoe acquired of the icy soil sample
for delivery to a TEGA oven.
Other bright material, especially around the
edges of the trench, is frost.
Trench is 2 in. Deep and 9 in. wide.
Wicked Witch material placed in oven and heated up to 35
degrees C (95 degrees F), well above the melting
temperature of ice.
Something in the sample melted at 0 degrees C (32 F) which
was identified as water ice.
How did we discover water on Mars?
Heated sampleEvidence it contained water:
1. Additional power to oven at 0 degrees C, 32 degrees F the
melting point of frozen water.
2. Pressure increase in the container that captured the gases
evolved from the oven that occurred at 0 degrees.
3. The data from the evolved gas analyzer.
Water chemical formula is 2 atoms of hydrogen linked to
1 atom of oxygen - H2O
The mass spectrometer identified this to be water.
Other evidence for
water on Mars-
Ice-cemented soils
uncovered 5 cm below
surface.
Three small chunks of
material seen in
shadow area of picture
from Sol 20 are gone by
Sol 24.
Material sublimated –
strong evidence for
water ice.
Trench is Dodo
PHYS 3380 - Astronomy
Water on Mars now?
PHYS 3380 - Astronomy
PHYS 3380 - Astronomy
Dark narrow streaks, called "recurring slope lineae," emanate from the walls of
Garni Crater on Mars, The dark streaks here are up to few hundred meters
long. They are hypothesized to be formed by flow of briny liquid water on Mars.
Measured hydrated salts in them - would lower the freezing point of a liquid
brine. It’s likely a shallow subsurface flow, with enough water wicking to the
surface to explain the darkening.
PHYS 3380 - Astronomy
Tidal Heating On Jupiter’s Moon’s
Gravitational tidal heating keeps the interiors of the three inner moons of Jupiter
hot
Moons have elliptical orbit and synchonous rotation
- as Ganymede completes one orbit, Europa completes exactly two orbits,
and Io completes exactly four orbits - moons periodically line up - causes
orbital ellipticity.
- tidal bulges are constantly being flexed in different directions - generates
friction inside
PHYS 3380 - Astronomy
Io
Jupiter’s tidal forces flex Io like a
ball of silly putty.
- friction generates heat
- interior of Io is molten
Volcanoes erupt frequently.
- sulfur in the lava accounts for
yellow color
- surface ice vaporizes and
jets away
Evidence of tectonics and impact
cratering is covered.
PHYS 3380 - Astronomy
Volcanic Plumes
PHYS 3380 - Astronomy
“Movie” (two frames) of the Tvashtar volcano on Io taken by New Horizon’s
spacecraft on the way to Pluto
PHYS 3380 - Astronomy
Europa
Metallic core, rocky mantle, and a crust
made of H2O ice
Its fractured surface tells a tale of
tectonics.
- few impact craters seen
- double-ridged cracks
- jumbled icebergs
These provide photographic evidence
of a subsurface ocean.
Europa has a magnetic field.
- implies liquid salt water beneath
the icy crust
Where liquid water exists, there could
be life!
PHYS 3380 - Astronomy
PHYS 3380 - Astronomy
Evidence of a Subsurface ocean
Jumbled crust with icebergs and surface cracks with double-ridged
pattern - caused by tidal flexing of thick layer of ice on top of liquid
ocean of water.
PHYS 3380 - Astronomy
Europa Ice Rafts
Thin, disrupted, ice crust in the Conamara region of Europa
- white and blue colors outline areas blanketed by a fine dust of ice
particles ejected at the time of formation of the large (26 kilometer in
diameter) crater Pwyll 1000 kilometers to the south.
- a few small craters - less than 500 meters in diameter were probably
formed at the same time as the blanketing occurred by large, intact,
blocks of ice thrown up in the impact explosion that formed Pwyll.
PHYS 3380 - Astronomy
Ganymede
Largest moon in the Solar System
Its surface has 2 types of terrain:
- heavily cratered, implies old
- long grooves, few craters, implies
young like Europa
It also has a magnetic field.
Could it have subsurface ocean?
- case not as strong as Europa’s
- tidal heating would be weaker
- would need additional heating
from radioactive decay
PHYS 3380 - Astronomy
Geyser-like eruptions of
ice particles and water
vapor shoot from the
south pole of Saturn's
moon, Enceladus
- arise from nearsurface pockets of
liquid water
- likely produce
Saturn's faint but
extended E ring.
PHYS 3380 - Astronomy
Cassini spacecraft
dove in October to
within 30 kilometers
of Enceladus, flying
right through -- and
sampling -- ice
geysers directly.
Observations support a mathematical model which treats the vents as nozzles that
channel water vapor from a warm, probably liquid source, to the surface at supersonic
speeds - theorizes that only high temperatures close to the melting point of water ice
could account for the large number of ice particles present in steady state in jets. A
liquid water source inside Enceladus could be similar to Earth's Lake Vostok, beneath
Antarctica, where liquid water exists beneath the ice. In Enceladus' case, the ice
grains would then condense from the vapor escaping from the water source and
stream through cracks in the ice crust to the surface and out into space.
PHYS 3380 - Astronomy
Largest moon of Saturn
• only moon known to
have a dense
atmosphere
• only object other than
Earth for which clear
evidence of stable
bodies of surface liquid
(methane) has been
found
• 98.4% nitrogen—the only
dense, nitrogen-rich
atmosphere in the solar
system aside from the
Earth’s
•
remaining 1.6%
composed of methane
and trace amounts of
other gases such as
hydrocarbons
Titan