Variability in Mars' Seasonal Polar Caps Observed by the Mars Odyssey Neutron Spectrometer Over Eight Mars Years
Abstract
The polar caps on Mars are dynamic regions that affect the global martian climate through the condensation each Fall/Winter of 25% of the atmosphere as CO2 frost on the surface in the polar regions, with subsequent sublimation in the Spring. One method of observing properties of the seasonal CO2 caps is neutron spectroscopy from orbiting spacecraft. Galactic cosmic rays (GCRs) bombard the surface of Mars producing spallation neutrons, which through scattering and excitation in the top meter of the martian surface lead to neutrons and gamma-rays that can be detected from orbit and provide unique information about surface geochemistry.
Mars Odyssey Neutron Spectrometer (MONS) has been in polar orbit around Mars since early 2002, measuring GCR-induced neutrons from the martian surface in three energy bands. Through these measurements, one can characterize the seasonal deposition and sublimation of CO2 frost through growth and recession rates and column-integrated mass. Such information provides unique benchmarking data for General Circulation Models, which are used to study Mars' atmosphere and climate history. MONS continues to operate today, providing a wealth of data to study variability in the seasonal CO2 cycle on present-day Mars. We have recently reprocessed eight Mars Years of data (MY 26 - 33, plus some data for MY 25 and 34) to study inter-annual variability. Initial results indicate that the global dust storm of MY 28 impacted the Northern seasonal cap properties in the Fall, Winter, and Spring immediately following the event. The observed trends (Fig 1 - reduction in thermal neutron counting rates, though no change in epithermal neutron counting rates were observed) may be due to a combination of cap properties, such as changes in CO2 deposition, deposition of an overlying later of hydrated dust molecules, and atmospheric properties, such as changes in atmospheric composition associated with breakdown of the polar vortex. The new data set, discussion of the observed variability and implications, and comparison of the MONS data to other observational techniques, will be presented.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.P41B3411M
- Keywords:
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- 0343 Planetary atmospheres;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 6225 Mars;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS;
- 5405 Atmospheres;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS;
- 5445 Meteorology;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS