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Mercury Atmospheric and Surface Composition Spectrometer (MASCS)

NSSDC ID: 2004-030A-04
Mission Name: MESSENGER


The MESSENGER Mercury Atmospheric and Surface Composition Spectrometer (MASCS) will use ultraviolet, visible, and near-infrared spectrometry to search for iron-related minerals on the surface of Mercury, to profile the distribution of various species with altitude, and to try to identify other species not previously detected. The primary objectives of this experiment are to help characterize the composition of the surface, the geologic history, and the nature of the exosphere. A total of roughly 2.7 Gb of data are expected over the nominal 1 year mission.

The MASCS experiment consists of two instruments, a UV/Visible Spectrometer (UVVS) and a Visible/IR Spectrograph (VIRS). A baffled 250 mm Cassegrain f/5 telescope focuses light through a common boresight to both instruments. The UVVS consists of an Ebert-Fastie diffraction grating spectrometer. An 1800 groove/mm grating gives an average spectral resolution of 1.0 nm (0.5 nm in the far ultraviolet). The grating is rotated in 0.25 nm steps for scanning. Three photomultiplier tubes are situated behind separate slits, one covers the far ultraviolet (115-190 nm), one the middle ultraviolet (160-320 nm), and one the visible (250-600 nm).

The instrument is optimized to observe weak atmospheric emissions but the far ultraviolet and middle ultraviolet detectors can also be used for surface reflectance measurements, the visible detector is protected from damage by a sensor which turns off the power before the field of view intercepts the sunlit planetary disk. The field of view is 1 x 0.05 degrees in the atmosphere and 0.023 x 0.023 degrees on the surface, it has a 25 km resolution at the limb.

The VIRS is designed to measure surface reflectance in the 0.3-1.45 micrometer band with a spatial resolution of 100 m to 7.5 km. The field of view is 0.023 x 0.023 degrees. Light reaches the detector through a fused silica fiber optic bundle. A concave holographic diffraction grating with 120 lines/mm and a dichroic beam splitter which separates the visible (0.30 - 1.025 micrometers) and infrared (0.95-1.45 micrometers) parts of the spectrum are used to focus the spectra on two detectors. The visible detector is a 512 pixel silicon line array with an absorption filter in front of the long-wavelength half to eliminate the second order spectrum. The infrared detector is a 256 pixel InGaAs line array which does not require cooling. Spectral resolution is 4 nm and data is digitized to 12 bits.

Alternate Names


Facts in Brief

Mass: 3.1 kg
Power (avg): 3.0 W
Bit rate (avg): 0.087 bps

Funding Agency

  • NASA-Office of Space Science Applications (United States)


  • Planetary Science: Atmospheres
  • Planetary Science: Geology and Geophysics

Additional Information

Questions or comments about this experiment can be directed to: Dr. David R. Williams.



NameRoleOriginal AffiliationE-mail
Dr. William E. McClintockExperiment ScientistUniversity of
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