Transcript The Interior of Mars

The Interior of Mars
Why do we need to know
about the interior?
Main reason: Because the chemical
composition and minerals inside can tell
us a lot about how the planet has formed
and evolved!!
Other reason: We can learn the process of
plume formation (which is mantle
upwelling) causing volcanisms on Mars.
Chemical Composition
• SNC meteorites can tell
us the chemical
compositions of magmas.
(Rocks are formed by
crystallization from a
cooling magma.)
• The most useful
meteorite types are
shergottities, which is the
S in SNC.
• Ex) Zagami found in
Nigeria, Africa in 1962.
Consists of 75%
pyroxene (pigeonite and
augite) and 18 %
plagioclase glass.
Study done by Driebus and Wanke
·Mid-1980s in Germany
They did a thorough study on the chemical
composition using the shergottites.
·Measured the abundances
of elements in shergottites
to estimate the abundances
in Mars mantle.
However…
• Driebus and Wanke were not satisfied with the result.
• So… they used carbonaceous chondrites.
• They found that the MnO (manganese oxide) abundance
in shergottites was about 0.48 wt%≈ in carbonaceous
chondrites.
• Assumption: The mantle of Mars has the same MnO
abundance as the carbonaceous chondrites.
• FeO/MnO (shergottites) (39.5) ÷ FeO/MnO
(carbonaceous chondrites) (100.6)=0.39. There is 0.39
of the FeO in the martian mantle of the FeO content of
the chondrites.
→FeO = 17.9 wt.%
Chemical Compositions of the
Mars and Earth (wt.%)
Compounds
Mars
Earth
SiO2
44.4
45.1
TiO2
0.1
0.2
Al2O3
3
4
Cr2O3
0.8
0.5
MgO
30.2
38.3
FeO
17.9
7.8
MnO
0.5
0.1
CaO
2.4
3.5
Na2O
0.5
0.3
K2O
0.04
0.03
Core of Mars
• Made comparison
with the
carbonaceous
chondrites.
• Iron – 77.8 wt.%
Nickel – 7.6 wt.%
Sulfur – 14.2 wt. %
Minerals in Mars
Experiment done by Bertka and Fei
• Purpose: To see how the
minerals change as
pressure/temperature
increases as depth
increases.
• Used a device called a
multi-anvil press – allows to
compress samples at
different pressures, and to
heat them at different
temperatures.
Results
• They found that at higher pressures, minerals
with higher densities were produced, while
the chemical composition remained the same.
• Refer to table 1.
• Ex) Mineral olivine (at 2Gpa)
→ crystal called gamma-spinel
(at 20Gpa).
More on how minerals change
Model of the mineralogy in
Martian Interior
• Refer to figure 1
• Note:
Uppermost mantle – olivine, pyroxene,
little bit of garnet
1100km – olivine → gamma-spinel
garnet and pyroxene → majorite
1850km – mixture of perovskite (mixture
of MgSiO3 and FeSiO), and
magnesiowustite (mixture of FeO and
MgO)
2000km – core-mantle boundary: metallic
core starts
Study done by Sohl and Spohn
•They constructed two different models.
• Model A – Satisfies
• Model B – Sastisfies the
Fe/Si=1.71 ratio, obtained
MI factor: C=0.366*Mprp2,
from the SNC meteorites.
also obtained from the
(However, MI:
SNC meteorites.
C=0.357*Mprp2)
(However, Fe/Si=1.35).
Considering the two models…
Here are the Results
•Fe-Ni-FeS core – size of a little less than one half of
the Mars’ radius
• On top of the core is a silicate mantle, which is
subdivided into lower spinel layer and upper olivine
layer.
• On top of the mantle is a basaltic crust, which is 100to 250-km in thickness.
• Surface heatflow density is 25 to 30 mW m-2.
• Calculated central pressure is about 40Gpa, and the
central temperature is about 2000 to 2200K.
Till now, we have learned about the
Martian interior by using….
• SNC meteorites
• Experiments
• Inner structure of
Earth as a
comparison
• Data of gravity,
rotation, and moment
of inertia.
What we need now is seismology
•Seismology is a study of marsquakes.
•Past attempts:
*Optimism seismometer was
onboard the small surface stations
of Mars 96, but there was a launch
failure.
*Seismometer onboard the Viking
lander failed as well.
*Seismometer onboard the Viking 2
lander – marsquake it detected
were not great due to a strong
wind and very low resolution.
Now…NetLander
• Goal – to study the metallic
core and the interior layers
• Seismometers will be carried
by a network of 4 landers.
--They will be flown one after
another, with a few days of
interval in-between.
-- They will be spread throughout
the planet.
NetLander contributions
• At first, the project was
supported by the
CNES, a French space agency,
and NASA.
• However, due to budgetary
problems,
NASA had to withdraw from the
project.
CNES had to end their entry
and landing
system activities.
→This project might be supported by
Europe and ESA (European Space Agency)
only.
To summarize
• Learned the chemical
composition of Mars
interior using SNC
meteorites. (Driebus and
Wanke’s study).
• Learned about the
mineralogy in Mars.
(Bertka and Fei’s study).
• Two models produced by
Sohl and Spohn.
• We need now seismology
– NetLander slowly on its
way.
References
• Bertka, C.M. & Yingwei F from Journal of Geophysical
Research. (1997).
• Lognonne, P., Giardini, D., et al. from Planetary and
Space Science. (2000, October).
• Lognonne, P., Giardini, D. from Astronomy & Geophysics.
(2003, August).
• Sohl, F. & Spohn, T. from Journal of Geophysical
Research, E. Planets. (1997, January 25).
• Taylor J.G. from Planetary Science Research
Discoveries. (1997, August 22)
• Website of European Space Agency
http://www.esa.int/export/esaCP/ESAZXCZ84UC_Expan
ding_0.html