Statistics
Scientific paper
Sep 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008epsc.conf..425z&link_type=abstract
European Planetary Science Congress 2008, Proceedings of the conference held 21-25 September, 2008 in Münster, Germany. Online a
Statistics
Scientific paper
Introduction The MESSENGER Fast Imaging Plasma Spectrometer (FIPS) [1] operated during the 14 January 2008 flyby of Mercury (M1) and provided the first composition measurements of Mercury's ionized exosphere and the ion plasma measurements of Mercury's magnetosphere. Ions in the mass/charge range 1 to ~60 amu/e were detected during the flyby period with a time-resolution of 8 s and within an energy range 0.1-13.5 keV/e. We will focus on three key results from this data set. First on the composition measurements of the ionized exosphere. The exosphere is found to be compositionally rich, with five key components in specific ranges of mass/charge. The identification of the specific elements is not unique because of limits to the FIPS counting statistics as well as the finite mass-resolution of FIPS. Second, we focus on the observations of multiply charged C and O observed in the magnetosphere. These particles are likely the result of impact ionization of hot electrons in the magnetosphere, and hence they provide an important indirect characterization of the magnetosphere. Third, we present an overview of the magnetospheric plasma properties as revealed by FIPS. Plasma moments are computed from what are at times partially obstructed velocity distributions. Our plasma moments are compared with magnetohydrodynamic simulations [2] of the magnetosphere. Exosphere Composition The exospheric composition is dominated by components in five ranges of mass/charge (m/q=23- 24, 32-35, 28, 39-40, and 17-19 amu/e) [3]. Even though the identification of the individual components is at times not unambiguous, FIPS measurements provide a rich set of constraints for the violent interactions of the space environment with Mercury's surface. The ionized exosphere is dominated by Na+ and Mg+, with a relative abundance that remains uncertain at this time due to limited counting statistics. The second mass/charge range most likely includes S+, O2 +, and/or H2S+, providing a first possible detection of S+ in the exosphere. More observations are needed distinguish among proposed sources [4]. Mass per charge 28 can be interpreted as Si+ or Fe++. This detection was complemented with very limited measurements of Fe+ at m/q=56. The next range provides a possible detection of K+ and Ca+, both of which are expected because neutral K and Ca are present in the exosphere. FIPS measurements may permit an estimate of the rate of ion implantation on Mercury's surface [5], of importance for understanding solar alteration of surface mineralogy and regolith properties. Finally, substantial fluxes at m/q = 17-19 suggest the presence of water compounds (H2O+, H3O+, OH+). These measurements point to a tight coupling between Mercury's exosphere and the planetary surface, through processes such as collisional sputtering and chemical sputtering [6]. Multiply Charged Components The MESSENGER FIPS data during the flyby EPSC Abstracts, Vol. 3, EPSC2008-A-00425, 2008 European Planetary Science Congress, Author(s) 2008 Fig. 1. MESSENGER first flyby geometry superposed on a plasma simulation by Kabin et al. [2]. X and Y are in units of Mercury radius. provided surprising evidence of highly charged ion components. Evidence of significant fluxes of C++ and O++ provide indirect evidence of hot electrons that interact with the exospheric plasma components. Plasma-sheet electrons appear to be the most likely ionization source for the creation of these ions, supporting an indirect detection of high-energy electrons by MESSENGER's X-Ray Spectrometer [7,8]. Magnetospheric Plasma FIPS also provided direct measurements of the magnetospheric plasma during the entire MESSENGER flyby. MESSENGER entered the magnetosphere from the tail side and exited toward the sunward direction, crossing the bow shock and the magnetopause with its associated plasma sheath, with a closest approach near the nightside of the planet (see Figure 1). Due to field-of-view obstructions from the MESSENGER sunshade and spacecraft, the observed velocity distributions are often incomplete, and an inversion requires model assumptions. The FIPS data indicate strong plasma heating at the magnetospheric boundary and document the evolution of the plasma throughout the magnetosphere. Conclusions The FIPS sensor has provided the first ion plasma measurements of Mercury's magnetosphere and ionized exosphere. The exosphere is found to be compositionally rich, with a significant number of atomic and molecular species. The measurements provide a first glimpse of Mercury's exosphere as a system that is highly connected through the incomplete shielding of Mercury's magnetic field from the solar wind, the interactions of the solar wind components with Mercury's surface, and the subsequent evolution of these particles in Mercury's small yet violent magnetosphere. References [1] Andrews, G. B. et al. (2007) Space Sci Rev., 131, 523. [2] Kabin, K. et al. (2000) Icarus, 143, 397. [3] Zurbuchen, T. H. et al. (2008) Science, in press. [4] Sprague, A. L. et al. (1995) Icarus, 118, 211. [5] Koehn, P. L. and Sprague A. L. (2007) Planet. Space Sci., 55, 1530. [6] Crider, D. H. and Vondrak R. R. (2000) JGR, 105, 26773. [7] Slavin, J. A. et al. (2008), Science, in press. [8] Mukai, T. et al. (2004) Adv. Space Phys, 33, 2166.
Gloeckler George
Killen Rosemary Margaret
Koehn Patrick L.
Krimigis Stamatios M.
McNutt Ralph L. Jr.
No associations
LandOfFree
Overview of Mercury's ionized exosphere and plasma environment: Results from the first MESSENGER flyby does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Overview of Mercury's ionized exosphere and plasma environment: Results from the first MESSENGER flyby, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Overview of Mercury's ionized exosphere and plasma environment: Results from the first MESSENGER flyby will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1793651