New discoveries from MESSENGER and insights into Mercury's exosphere (original) (raw)
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The MESSENGER mission to Mercury: scientific objectives and implementation
Planetary and Space Science, 2001
Mercury holds answers to several critical questions regarding the formation and evolution of the terrestrial planets. These questions include the origin of Mercury's anomalously high ratio of metal to silicate and its implications for planetary accretion processes, the nature of Mercury's geological evolution and interior cooling history, the mechanism of global magnetic ÿeld generation, the state of Mercury's core, and the processes controlling volatile species in Mercury's polar deposits, exosphere, and magnetosphere. The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission has been designed to y by and orbit Mercury to address all of these key questions. After launch by a Delta 2925H-9.5, two ybys of Venus, and two ybys of Mercury, orbit insertion is accomplished at the third Mercury encounter. The instrument payload includes a dual imaging system for wide and narrow ÿelds-of-view, monochrome and color imaging, and stereo; X-ray and combined gamma-ray and neutron spectrometers for surface chemical mapping; a magnetometer; a laser altimeter; a combined ultraviolet-visible and visible-near-infrared spectrometer to survey both exospheric species and surface mineralogy; and an energetic particle and plasma spectrometer to sample charged species in the magnetosphere. During the ybys of Mercury, regions unexplored by Mariner 10 will be seen for the ÿrst time, and new data will be gathered on Mercury's exosphere, magnetosphere, and surface composition. During the orbital phase of the mission, one Earth year in duration, MESSENGER will complete global mapping and the detailed characterization of the exosphere, magnetosphere, surface, and interior.
Observations of Mercury's Exosphere during the First MESSENGER Flyby
… Proceedings of the …, 2008
Observations of Mercury's tenuous exosphere were taken with the UltraViolet and Visible Spectrometer (UVVS) of the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) during MESSENGER's first Mercury flyby on January 14, 2008 [1]. ...
Measurement of neutral atoms and ions in Mercury's exosphere
Planetary and Space Science, 2001
ABSTRACT The Mercury apparatus for ions and atoms (MAIA) is a linear time-of-flight mass spectrometer operating in two modes, a neutral mode and an ion mode, which are used alternatively. MAIA is designed to determine the composition of Mercury's exosphere and possibly its crust. The mass resolution of MAIA is sufficient to resolve all elements up to mass . In both optional modes the mass range extends from 1 to , and, if required, it can be increased up to by changing the data acquisition mode. Even isotopes could be resolved, however, the partial pressures at Mercury are most likely too low for identification.
Mercury's exosphere origins and relations to its magnetosphere and surface
Planetary and Space Science, 2007
Mariner 10, the only spacecraft that ever passed close to Mercury, revealed several unexpected characteristics: an intrinsic magnetosphere, the highest mean density of any Solar System terrestrial planet and a very thin non-collisional atmosphere. Mercury's atmosphere is very poorly explored since only three atomic elements, H, He and O, were observed during the three flybys of Mariner 10. The measurements done by radio and solar occultations provided upper limits on the neutral and ion densities. These measurements pointed out the close connection between species in Mercury's exosphere and its surface, which is also the case for the Moon. Mariner 10 observations also characterized the vertical distributions and the day to night contrasts of Mercury's exosphere for its lightest components H and He (
The Mercury Atmospheric and Surface Composition Spectrometer for the MESSENGER Mission
Space Science Reviews, 2007
The Mercury Atmospheric and Surface Composition Spectrometer (MASCS) is one of seven science instruments onboard the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft en route to the planet Mercury. MASCS consists of a small Cassegrain telescope with 257-mm effective focal length and a 50-mm aperture that simultaneously feeds an UltraViolet and Visible Spectrometer (UVVS) and a Visible and InfraRed Spectrograph (VIRS). UVVS is a 125-mm focal length, scanning grating, Ebert-Fastie monochromator equipped with three photomultiplier tube detectors that cover far ultraviolet (115-180 nm), middle ultraviolet (160-320 nm), and visible (250-600 nm) wavelengths with an average 0.6-nm spectral resolution. It will measure altitude profiles of known species in order to determine the composition and structure of Mercury's exosphere and its variability and will search for previously undetected exospheric species. VIRS is a 210-mm focal length, fixed concave grating spectrograph equipped with a beam splitter that simultaneously disperses the spectrum onto a 512-element silicon visible photodiode array (300-1050 nm) and a 256-element indium-gallium-arsenide infrared photodiode array 850-1,450 nm. It will obtain maps of surface reflectance spectra with a 5-nm resolution in the 300-1,450 nm wavelength range that will be used to investigate mineralogical composition on spatial scales of 5 km. UVVS will also observe the surface in the far and middle ultraviolet at a 10-km or smaller spatial scale. This paper summarizes the science rationale and measurement objectives for MASCS, discusses its detailed design and its calibration requirements, and briefly outlines observation strategies for its use during MESSENGER orbital operations around Mercury.
The unique two-point measurements of neutrals and ions at Mercury, obtained by the MESSENGER spacecraft during its 14 January and 6 October 2008 Mercury flybys, provide the first opportunity to constrain the transport of heavy ions in this reconnecting magnetosphere. Models of exospheric transport and of ion circulation of two major species, sodium and magnesium, are combined with MESSENGER observations to investigate the effect of planetary ions on the properties of Mercury's magnetosphere. Under northward interplanetary magnetic field (IMF), the condition that prevailed during the first flyby, finite gyro-radius effects lead to increased penetration of pickup ions into the dusk magnetosphere. In contrast, under southward IMF the planetary ion distributions are dominated by the open magnetopause boundary and the formation of a near-tail X-line, leading not only to increased penetration of pickup ions into the magnetosphere, but also to increased ``leakage'' to the solar...
2012
Orbital gamma-ray measurements obtained by the MESSENGER spacecraft have been analyzed to determine the abundances of the major elements Al, Ca, S, Fe, and Na on the surface of Mercury. The Si abundance was determined and used to normalize those of the other reported elements. The Na analysis provides the first abundance estimate of 2.9 AE 0.1 wt% for this element on Mercury's surface. The other elemental results (S/Si = 0.092 AE 0.015, Ca/Si = 0.24 AE 0.05, and Fe/Si = 0.077 AE 0.013) are consistent with those previously obtained by the MESSENGER X-Ray Spectrometer, including the high sulfur and low iron abundances. Because of different sampling depths for the two techniques, this agreement indicates that Mercury's regolith is, on average, homogenous to a depth of tens of centimeters. The elemental results from gamma-ray and X-ray spectrometry are most consistent with petrologic models suggesting that Mercury's surface is dominated by Mg-rich silicates. We also compare the results with those obtained during the MESSENGER flybys and with ground-based observations of Mercury's surface and exosphere.