# Mars (Solar System) by Linda Elkins-Tanton

By Linda Elkins-Tanton

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Without the oxygen and water, more of the iron in the Earth would sink to the core as metal instead of bonding with oxygen and remaining in the mantle. The problem of depleted alumina in the Martian mantle is harder to explain. Calling on a bulk composition for Mars that is significantly different from the Earth’s challenges current concepts of planetary accretion in the early solar system; adjacent planets should have similar compositions. Still, Mars may have formed from material with less alumina than the Earth.

1 J/º kg). 2 calories of energy are required to raise the temperature of one pound of silicate material one degree. Here is a sample calculation. A planetesimal is about to impact a larger body, and the planetesimal is a kilometer in radius. 7 ϫ 1013 kg), if its density were about 250 lb/ft3 (4,000 kg/m3). 5 ϫ 1020 J ϭ 2 ϫ 1020 cal (continues) 37 38 B Mars Accretion and Heating: Why Are Some Solar System Objects Round and Others Irregular? 1 J/ºkg The question now becomes, how much mass is going to be heated by the impact?

This is the equation that allows geologists to determine the age of materials based on radiogenic systems. The material in question is ground up, dissolved in acid, and vaporized in an instrument called a mass spectrometer. The mass spectrometer measures the relative abundances of the isotopes in question, and then the time over which they have been decaying can be calculated. The values of D and n are measured for a number of minerals in the same rock, or a number of rocks from the same outcrop, and the data is plotted on a graph of D v.