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 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.%) Compound sMarsEarth SiO TiO Al 2 O 3 34 Cr 2 O MgO FeO MnO CaO Na 2 O K2OK2O

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 Model A – Satisfies Fe/Si=1.71 ratio, obtained from the SNC meteorites. (However, MI: C=0.357*M p r p 2) Model B – Sastisfies the MI factor: C=0.366*M p r p 2, also obtained from the SNC meteorites. (However, Fe/Si=1.35). They constructed two different models.

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.

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 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. Seismology is a study of marsquakes.

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 ding_0.html