Lecture 15

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Lecture 15Mars CH4, MER Rovers, SNC
Meteorites/Loss of Heavy Gases

• Meteo 466

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Is there CH4 in Mars present atmosphere?
M. J. Mumma, Science (2009)

• Mumma is doing high-resolution spectroscopy
  using the (10-m) Keck
• telescopes in Hawaii
• The martian CH4 lines, while weak, are Doppler
  shifted relative to Earth

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Martian CH4 Spatial variability?

• Mumma sees evidence for both spatial and
  temporal variability
• This is curious, as the estimated photochemical
  lifetime of CH4 in
• Mars atmosphere is 300 years!

M. J. Mumma, Science (2009)
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Methane on Mars?(From Mars Express Planetary
Fourier Spectrometer)
0 ppbv CH4
10-50 ppbv CH4
H2O
H2O
H2O
CH4 (3018 cm-1)
Solar
Formisano et al., Science Express (28 Oct., 2004)
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CH4 Spatial Variability
High CH4
Med CH4
Low CH4
Formisano et al., Science Express (28 Oct., 2004)
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MER Rovers

• Two rovers Spirit and Opportunity
• Arrived at Mars in early 2004
• Still operating!
• Design lifetime was for 3-6 months

Courtesy of Joy Crisp
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Meridiani Planum
Opportunity
Spirit
Gusev Crater

• Both rovers landed near the edge of the southern
  highlands

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Spirit RoverGusev Crater

• Gusev Crater was picked as a landing site because
  it is at the base of an ancient river channel

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Husband HillGusev Crater

• Lots of rocks and dust!

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Opportunity landing site
Endurance crater
Eagle crater
Image from Wikipedia
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OpportunityEagle crater

• First panoramic view taken by the Opportunity
  rover
• The rover would later investigate the outcrops
  at the upper right

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Endurance crater (Opportunity)
Courtesy of Darren Williams
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Blueberries
From Opportunity rover at Meridiani Planum
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Spherules (Blueberries) on Mars
(False color image)
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Opportunity roverMeridiani Planum

• Lots of hematite, in the form of blueberries
• Also see evidence for sulfate evaporites
• Both are evidence for standing water
• Doesnt tell you much about surface temperature,
  though, because sulfate solutions have low
  freezing points

Courtesy of NASA
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Sulfuric Acid as Anti-Freeze
Courtesy of Andy Knoll
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• Blueberries are made of hematite (Fe2O3)
• Liquid water is required for their formation

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Crossbedding?

• Standing liquid water (no ice cover) is probably
• required to form these patterns (John
  Grotzinger, MIT)

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• Well return to the evidence for liquid
• water in Mars past in the next lecture..

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Famous martian meteorite
Notation ALH Alan Hills (Antarctica)
84 collected in 1984 001 first
sample collected
D. S. McKay et al., Science (1996)
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Martian nannobacteria?
50 nm

• Pictures like this, taken with SEM (scanning
  electron microscopy), were
• argued to represent possible martian
  nannofossils
• Bacteria on Earth, however, are much larger (r gt
  500 nm, or 0.5 ?m)

D. S. McKay et al., Science (1996)
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SNC meteorites (from Mars)

• SNC Shergotty, Nahkla, Chassigny
• Formed in a strong gravitational field
• Different O isotopic composition than Earth
• See next slide
• Some (like this one) have glasses that contain
  trapped gases

http//www.jb.man.ac.uk/distance/strobel/ solarsys
/solsysc.htm
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3-isotope diagram for oxygen

• The Earth, the Moon, and enstatite chondrites
  all fall along
• a single mass fractionation line
• SNC meteorites are enriched in 17O by about 0.5

http//www.nature.com/nature/journal/v416/n6876/fi
g_tab/416039a_F3.html
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SNC noble gases vs. martian atmosphere (from
Viking)

• The pattern (and absolute abundances) of noble
  gases matches exactly with that measured by the
  Viking mass spectrometers
• N2 and CO2 abundances are also the same
• 15N/14N ratio is also the same ( 1.62 x Earths
  value)

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Mars N isotope fractionation

• 14N is lighter than 15N hence
• It is more abundant in the upper atmosphere
• It escapes more readily
• Photochemical escape
• N2 h? ? N2 e (? ? 79.6 nm)
• N2 e ? N N (dissociative recombination)
• When this happens, you get back the ionization
  energy 79.6 nm 15.6 eV
• (1 eV 1 electron volt 1.602?10-12 ergs)

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Nitrogen escape from Mars

• How much energy goes into the N atoms depends on
  their electronic state
• Ground state N(4S)
• First excited state N(2D)
• Possible reactions Kinetic energy
• N2 e ? N(4S) N(4S) (Doesnt go)
• N2 e ? N(4S) N(2D) 1.73 eV each
• N2 e ? N(2D) N(2D) 0.53 eV each

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Nitrogen escape from Mars

• Calculate velocities
• KE ½ mv2 ? v (2 KE/m)0.5
• For reaction ii
• N2 e ? N(4S) N(2D) 1.73 eV each
• v(14N) 4.87 km/s
• v(15N) 4.70 km/s
• Compare with escape velocity
• vesc (2GM/rc)0.5 4.88 km/s
• ? 14N escapes much more readily than 15N!
  Consequently, Mars has the largest 15N/14N ratio
  in the Solar System.

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Photochemical escape of oxygen from Mars

• Dissociative recombination of ions containing O
  atoms can lead to escape of oxygen
• O2 e ? O O(1D) 2.5 eV each
• CO e ? C O 1.25 eV for O
• 
  1.66 eV for C
• CO2 e ? CO O 3 eV for CO
• 
  5.3 eV for O
• Energies needed to escape
• O 1.99 eV C 1.49 eV
• ? Both O and C can escape!

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• Heavy gases can also be lost from Mars via
  sputtering by the solar wind
• By contrast, the solar wind is held off from
  Earths atmosphere/ionosphere by Earths magnetic
  field ?

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Earth magnetosphere/solar wind interaction
http//www.cem.msu.edu/cem181h/projects/97/solar/
index.htm
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Mars ionosphere/solar wind interaction

• In the case of low solar wind pressure, the
  sunward side of the ionosphere is thick (the red
  region) and some of the atmosphere can be seen
  trailing off behind the planet.

http//svs.gsfc.nasa.gov/vis/a000000/a002900/a0029
62/index.html
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Mars ionosphere/solar wind interaction

• For the faster solar wind, the Martian ionosphere
  becomes thinner and much more planetary
  atmosphere is scavenged by the solar wind

http//svs.gsfc.nasa.gov/vis/a000000/a002900/a0029
62/index.html
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Coupled O and H escape from Mars

• H can escape from Mars by 2 mechanisms
• Jeans escape
• Sputtering by solar wind
• O can escape photochemically or by sputtering
• If H and O escape in a 21 ratio, then H2O is
  being lost
• Feedback could work by controlling H2 and O2
  levels in the martian lower atmosphere
• This used to be a popular idea
• It now seems more likely that H escape is
  balanced largely by surface oxidation