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Lecture 5 : Mars, Earth, and The Outer Planets

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Life on Mars? ... today is whether life existed on Mars in the past, and ... in the 1970s, tested directly for the existence of life on the surface of Mars. ... – PowerPoint PPT presentation

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Title: Lecture 5 : Mars, Earth, and The Outer Planets


1
Lecture 5 Mars, Earth, and The Outer Planets
  • Robert Fisher

2
Items
  • Tutor Akiva Bhansali has hours Monday 4 - 6 PM,
    Tuesday 4 - 8 PM on the 12th floor lounge
    (possibly 14th floor if 12th floor is crowded.)
  • Solution sets 1-3 has been posted to the website.
  • Problem set number 4 has been posted to the
    website.
  • Midterm 1 is in two weeks.
  • Everything through next weeks lecture will be on
    the exam.
  • Exam will be multiple-choice and true/false
    questions.
  • The exam will be one hour long.
  • After the exam, well take a break and return to
    lecture.
  • No homework will be due in two weeks on the day
    of the first midterm.
  • First observational project will be distributed
    in two weeks, following the exam.
  • Late Homeworks

3
Sample Midterm Question
  • Which of the following inner solar system bodies
    is most similar to Mercury in terms of surface
    properties?
  • A) Venus
  • B) Earth
  • C) Moon
  • D) Mars

4
Sample Midterm Question
  • Which of the following statements is false?
  • A) At the location of Chicago, the sun is never
    visible at the zenith.
  • B) At the location of the North Pole, all visible
    stars are circumpolar stars.
  • C) At the location of the Equator, all stars are
    visible at some point in the year.
  • D) At the location of the South Pole, the
    celestial equator is at the Meridian.

5
Review Week 3
  • Keplers Three Laws
  • Newtons Three Laws
  • Spectra -- Continuum, Absorption, Emission

6
Review Week 4
  • Solar System Overview
  • Sun
  • Planets
  • Moons/Rings
  • Dwarf Planets, Asteroids, Kuiper Belt Objects,
    Comets, Meteors
  • Mercury
  • Venus

7
Todays Material
  • Mars, Earth
  • The Outer Solar System

8
Mars
9
Mars
  • The red planet Mars is the current focus of
    NASAs unmanned interplanetary missions, because
    it is believed to have once harbored a warm,
    moist Earth-like phase -- possibly even life.
  • There are several similarities between Earth and
    Mars.
  • Mars orbits the sun at 1.5 AU.
  • Its axis is tilted at 25 degrees.
  • Its day is nearly identical to one Earth day.

10
A Visual Comparison of Earth and Mars
11
Canals on Mars??
  • In 1877, Italian astronomer Giovanni Schiaparelli
    described features he saw on Mars as canali,
    which is probably best translated as channels.
  • This phrase became mistranslated as canals,
    which suggested to some astronomers that the
    features seen were artificially-created.
  • Later space missions have uncovered tons of
    evidence for water on Mars, including channels
    like those Schiaparelli claimed to have seen.
    They are, however, far too small to be visible
    from Earth, even with the largest telescopes
    available.

12
Schiaparellis Drawing of Mars
  • Although primitive photographic plates existed at
    that time, Schiaparelli recorded his observations
    in drawings, which he believed to be more
    accurate than photographic plates.

13
Canals on Mars??
  • Other astronomers (most noteably Percival Lowell)
    became fascinated with the concept, and
    astronomical research of Mars has flourished
    since.
  • Despite the body of work, it is likely that
    Schiaparellis canals were a physiological fluke,
    though the explanation is still sometimes debated
    today.
  • These canals gave rise to the wealth of Martian
    science fiction -- from Edgar Rice Burroughs to
    H.G. Wells to Ray Bradbury, and many, many more
    -- which in turn inspired real planetary
    scientists like Carl Sagan and many others.

14
Early Martian Astronomy
15
A Flyover Overview of Mars
16
Mars vs. Earth
  • Mars is much smaller than the Earth, with a
    radius about half that of Earth, and a mass of
    about a tenth the Earths.
  • The surface temperature today is far below the
    freezing point of water.
  • Even if one could warm water ice on Mars today,
    it would go directly into a gaseous state without
    becoming liquid because of the thin atmosphere.
  • It has two tiny moons, Phobos and Deimos, with
    properties radically different than Earths moon.
  • While tilt is similar to that of Earth today, the
    tilt angle oscillates wildly over tens and
    hundreds of millions of years.
  • It has only a weak magnetic field in its crust,
    and lacks a magnetic core.

17
Phobos and Deimos The Moons of Mars
  • Mars has two tiny moons located very near the
    planets surface -- the closest moons to any
    planet in the solar system.
  • It is thought they were asteroids intersecting
    the Martian orbit captured via drag through an
    early, thicker Martian atmosphere.

Phobos
Deimos
18
Asaph Hall, Discoverer of Phobos and Deimos
19
From The Observatory, 1877
20
Phobos and Deimos
  • An orbiting body at one specific radius has an
    orbital period equal to the rotational period of
    the planet -- a geosynchronous orbit. From the
    planet, the body would appear to be stationary.

21
Phobos
  • Phobos orbits well inside Martian Geosynchronous
    orbit, and so
  • appears to rise in the west and set in the east

22
Deimos
  • Deimos orbits outside of Martian geosynchronous
    orbit, and remains visible for two nights in a
    row.

23
Mars Odyssey - How to Get to Mars
24
Olympus Mons, The Largest Volcano in the Solar
System
  • Olympus Mons is roughly three times the height of
    Mount Everest, but is much broader, with
    shallower sides.

25
Digitally-Reconstructed Flythrough of Valles
Marineris from Mars Odyssey
26
Crevasses on Martian Polar Icecap, Revealed by
Martian Global Surveyor
27
What Can Cause These Variations in the Martian
Climate?
  • The leading explanation for the stratification in
    the Martian polar cap is the variation in the
    Martian rotational and orbital properties.
  • All planets are perturbed in the orbits about
    the sun by gravitational influences from the
    other planets, particularly Jupiter
  • Mars is particularly susceptible to these
    perturbations because
  • It is the closest planet to Jupiter
  • It lacks a large moon (like Earth) to dampen
    out the effects

28
Variation in Martian Obliquity and Orbital
Eccentricity
  • Researchers have found that both the angle of
    inclination of the Martian rotation (obliquity)
    and the eccentricity of its orbit vary wildly
    over a timescale of millions of years -- leading
    to alternating epochs of warm and cold climate

Today
Earth
Mars
29
Variation in Martian Obliquity and Orbital
Eccentricity
  • Researchers have modeled the effects of the
    variation of Martian obliquity and orbital
    eccentricity, and found that they in fact do
    naturally lead to variations in the amount of
    power the Martian surface receives, on the
    timescale of millions of years

30
Water on Mars
  • Multiple lines of evidence compiled over many
    years strongly suggest that Mars had abundant
    liquid water on the surface in the distant past,
    and may even have frozen water just beneath the
    surface today.
  • One line of evidence comes from images of the
    surface -- suggestions that the morphology, or
    shapes, suggests the presence of water.
  • Another line of evidence comes from direct
    surface measurements made by the Rovers sent to
    the surface.
  • A third line of evidence comes from imaging
    instruments on orbiters which detect hydrogen --
    a key component of water.

31
Riverbeds on Mars
  • Many regions on Mars show what appear to be signs
    of meandering, dry riverbeds.

32
Evidence for Flooding on Mars
  • Evidence for massive erosion from floods can be
    seen on the surface of Mars today, for instance
    in the Ares Vallis.

33
Catastrophic Floods on Earth
  • Similar catastrophic floods have occurred on the
    Earth as well, for instance in the Washington
    State Scablands. These were believed to have been
    formed from massive floodwaters a thousand feet
    (!!) deep.

34
Seepage Channels
  • Various craters and valleys on Mars show signs of
    runoff in the recent past.

Newton Crater
35
Seepage Channels
  • While liquid water cannot exist on the surface of
    Mars today, it is possible that these runoff
    regions develop only after subsurface liquid
    water has burst through a dam of frozen surface
    water.
  • This water would be boiling away violently, and
    so these events must develop suddenly and
    disappear rapidly.
  • Similar behavior occurs in ice flows in
    Antarctica on the Earth.

Side View
Rock/Liquid Water
Rock/Ice
36
Where Did All That Water Go?
  • Very good evidence exists that a LOT of liquid
    water once ran on the surface of Mars in the
    past. Where did all of that water go?
  • Because the atmospheric pressure is so low on
    Mars today, any water on the surface of Mars
    today will evaporate in the first global warming
    cycle
  • Some water may be buried in layers of CO2 ice at
    the poles of Mars
  • However, the leading explanation has been that
    the water has become frozen beneath the surface
    of Mars.

37
Permafrost on Earth
  • The situation on Mars is analogous to permafrost
    on Earth, where regions (mostly inside the arctic
    circles) have water frozen in the surface
    year-round.

38
Mars Odyssey Neutron Maps
  • In 2002, Mars Odyssey imaged Mars in neutrons,
    scanning for hydrogen-rich material just beneath
    the surface.

39
Odysseys Hydrogen Map of Mars
  • Odyssey found bands of hydrogen-rich material
    around both the north and south poles of Mars --
    possibly due to frozen water.

40
Surface Water on Mars
  • In the very distant past -- billions of years ago
    -- Mars appears to have had abundant surface
    liquid water. It is possible that the
    lowest-lying areas on the surface, particularly
    in the Northern hemisphere, were submerged in a
    giant ocean.
  • Mars climate eventually became unsuited to
    liquid water at the surface, and most of it was
    probably lost over time to atmospheric
    evaporation.
  • The remaining water became frozen into the
    surface in a kind of permafrost, similar to that
    on arctic regions on Earth.

41
Life on Mars?
  • Because there is excellent evidence suggesting
    that large amounts of surface water existed in
    the past on Mars, it is natural to think that
    life may have existed on Mars as well.
  • One of the biggest questions that one can ask
    today is whether life existed on Mars in the
    past, and may possibly even exist today.
  • The pioneering Viking 2 lander, launched by NASA
    in the 1970s, tested directly for the existence
    of life on the surface of Mars.

42
Question
  • How would you construct a test for life on
    another planet?

43
Viking 2 Lander Model
44
Viking 2 Lander on Surface of Mars
45
Viking 2 Tests for Life
  • The Viking 2 mission to Mars contained a
    highly-sophisticated scientific package with four
    experiments designed to detect the presence of
    life in the Martian surface soil.

46
Wheres the Carbon?
  • One experiment, the gas chromatograph - mass
    spectrometer - took a scoop of Martian soil,
    vaporized the soil and analyzed the composition
    of the resulting chemicals.
  • The idea was to test for the presence of
    carbon-bearing compounds, which are the hallmark
    of organic chemistry and life on Earth.
  • The result was a stunning negative - there is
    even less organic material on Mars than in the
    lunar regolith.

47
The Labeled Release Experiment
  • Perhaps the most clever of the Viking experiments
    was the labeled release experiment, which put a
    drop of liquid nutrient bearing seven organic
    molecules metabolized by microorganisms on Earth.
  • The trick was to tag each of the carbon molecules
    using a very rare isotope of radioactive carbon
    14.
  • Amazingly, this test produced a measurable
    response.

48
How to Reconcile the Viking Measurements?
  • How can one reconcile the two Viking measurements?

49
The Earth
We shall not cease from exploration, and at the
end of all our exploring will be to arrive where
we started and know the place for the first
time.
-- T.S. Eliot, Little Gidding
50
Earth
  • Earth is superficially similar in many respects
    to both Venus and Mars, in terms of its
    composition, size, and so on.
  • The primary features which distinguish Earth is
  • Existence of a major moon.
  • Relatively strong magnetic field.
  • Abundant surface water.
  • Life.

51
Greenhouse Effect Demo
52
Coriolis Demo (2/2)
53
Circulation Demo
54
Greenhouse Effect
  • Molecules in the atmosphere are transparent to
    visible light, but absorb radiation in the
    infrared.
  • Fundamentally, this is because individual atoms
    in molecules can rotate and vibrate at energies
    much lower than electrons in atoms.
  • These lower-energy transitions typically occur in
    the infrared portion of the spectrum.

Diatomic Molecule
55
Coriolis Demo (1/2)
56
Long-Term Stability of Earths Climate
  • Physicists and other scientists will often
    characterize a system by its equilibrium and
    stability.
  • For instance, a ball may be instantaneously in
    balance -- in equilibrium -- but that balance may
    be either stable or unstable.

Stable
Unstable
57
Earths Climate
  • Up until now, Earths climate has been stable

58
Earths Climate
  • The trend of global warming has been pronounced
    in the last one hundred and fifty years.

59
Carbon Dioxide Emissions
  • The trend of heating is correlated with increased
    greenhouse gas emissions.

60
Astronomical Context
  • We have seen that Earth is unique in the solar
    system.
  • Runaway greenhouse heating resulted in the
    hellish world of Venus.
  • Insufficient greenhouse heating resulted in the
    frigid world of Mars.
  • Has mankind upset the delicate climate
    equilibrium on Earth?

61
Outer Planets
62
Gas Giant Planet Interiors
  • Each of the gas giants is thought to have a rocky
    core interior about the size of the Earth or
    greater, overlaid by thick gaseous atmospheres.

63
Next Week -- Midterm!
  • We will begin to cover the Outer Planets.
  • First midterm next week!
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