Space/Science — HabitableZone

Space/Science » in reply to Ice sheets are cool.

Geoid modeling
Gary — (archived)

JMS said:

"Pleisotcene ice sheets ... were big enough to alter the geooid of the planet.

We mathematically model a planet's geoid using similar methods to modelling the gravitational field (no big surprise). The J2 harmonic correlates to a planet's oblateness. For heatshield design work, an ellipsoid model for the Earth is good enough. For Venus, a plain sphere is adequate (almost no oblateness). However Mars has a very irregular shape so a full blown spheroidal model is required. I take my model up to 5 x 5 terms. If memory serves me correctly, the Martian surface can vary over 3 km. from a perfect circle along the equator. This isn't common knowledge but the old Martian atmospheric models (COSPAR-NS) are obsolete because the zero altitude was based upon an inaccurate reference ellipsoid. It's interesting that a planet's geology plays a role in designing spacecraft heatshields.

Gary

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