The Annual Heat Balance of the Martian Polar Caps from Viking Observations

• Main Author: Paige, David Abbey, Jr.
• Format: Thesis
• Language: English
• Published: 1985
• Subjects: South Pole; North Pole; South pole
• Online Access: https://thesis.library.caltech.edu/5720/; https://thesis.library.caltech.edu/5720/1/Paige_da_1985.pdf; https://resolver.caltech.edu/CaltechTHESIS:04162010-092926816

This thesis presents the first measurements of the annual heat budgets of the polar caps of Mars from spacecraft observations. The primary motivation for this work is to understand why seasonal CO 2 frost deposits at the north pole of Mars disappear in the summer, whereas seasonal CO 2 deposits near the south pole do not. This behavior is not expected to first order because both Martian poles receive the same total amount of sunlight at the top of the atmosphere over the course of a year. Understanding why the Martian north and south polar caps behave in an asymmetric fashion is important because the vapor pressures of permanent polar CO 2 deposits determine the planet-wide surface pressures of CO 2 gas, which is the dominant constituent of the Martian atmosphere. Annual radiation budgets for the core regions of the north and south polar caps are determined from solar reflectance and infrared emission observations obtained by the Infrared Thermal Mappers (IRTMs) aboard the two Viking orbiters. The results show that the absence of CO 2 frost at the north pole during summer is primarily due to an asymmetry in the rates of CO 2 frost sublimation at surface in the north and south during spring. Further analysis traces this difference to seasonal frost reflectivities being approximately 20% lower in the north than in the south during late spring. It is shown that seasonal frost deposits at the poles demonstrate a remarkable tendency to not become darker when contaminated with dust, and to become brighter with increasing rates of solar illumination. Since peak solar illumination rates are presently higher at the south pole than the north pole because of the large eccentricity of Mars' orbit, the tendency for the frost to become brighter with increasing rates of solar illumination explains the asymmetry. The tendency for the frost to not become darker when contaminated by dust explains why the seasonal behavior of the Martian polar caps is highly repeatable from year to year despite interannual variations in the ...