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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!!

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The Interior of Mars

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  1. The Interior of Mars

  2. 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.

  3. 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.

  4. 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.

  5. 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.%

  6. Chemical Compositions of the Mars and Earth (wt.%)

  7. Core of Mars • Made comparison with the carbonaceous chondrites. • Iron – 77.8 wt.% Nickel – 7.6 wt.% Sulfur – 14.2 wt. %

  8. Minerals in MarsExperiment 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.

  9. 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).

  10. More on how minerals change

  11. 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

  12. Model A – Satisfies Fe/Si=1.71 ratio, obtained from the SNC meteorites. (However, MI: C=0.357*Mprp2) Model B – Sastisfies the MI factor: C=0.366*Mprp2, also obtained from the SNC meteorites. (However, Fe/Si=1.35). Study done by Sohl and Spohn • They constructed two different models.

  13. 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 100- to 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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_Expanding_0.html

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