Re-Analysis of the 1976 Mars Occultation of Epsilon Geminorum
Abstract
Introduction: Stellar occultations utilize the line-of-sight alignment of a star with a solar system body in order to measure properties of neutral atmospheres. A particularly fortuitous observation, the occultation of ɛ Geminorum by Mars on April 8, 1976 remains the brightest stellar occultation of Mars to date. This occultation was observed in three channels by the 91 cm telescope aboard the Kuiper Airborne Observatory and the original analysis was published in 1977 just after the arrival of Viking 1 at Mars [1].
Motivation and Aims: The original analysis made a number of assumptions and limitations no longer required today. These include favoring analytical expressions over exact solutions, omitting full error propagation, and binning the original 4 ms time resolution to 0.1 s [1, 2]. Relaxing the latter is a fundamental tenant of this work—we believe this high-resolution observation contains detailed structure on the Martian atmosphere not identified in the original work. Furthermore, we interpret our results in the context of the many orbital remote sensing and in situ measurements taken, as well as atmospheric models deployed, in the past 43 years. Methods: We use an improved computational procedure closely following the steps of the original work [3]. Normalized stellar flux is fit to an isothermal model to set an upper boundary condition for inversion. Inversion begins at 90% stellar flux and first integrates time resolution into altitude resolution of occultation ray penetration depth and into differential refractivity. The latter is inverted to determine neutral number density, temperature, and pressure at all altitudes [1, 3]. Error is carefully propagated by taking partial derivatives at each integration step [3]. Results: Our work shows a significant increase in vertical resolution of atmosphere profiles in comparison to the original work. Notably we find approximately 5 km-wavelength temperature fluctuations not identified in the original work, which may be vertically propagating waves. We also report our findings on the climatic shifts of the Martian atmosphere in the years since these data were taken. References: [1] J. L. Elliot et al. (1977) ApJ, 217, 661-679. [2] R. G. French, J. L. Elliot, and P. J. Gierasch (1978) Icarus, 33, 186-202. [3] Elliot, J. L., Person, M. J., & Qu, S. (2003) AJ, 126, 1041-1079.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.P41B3425S
- 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