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mercury atmosheric and surface composition spectrometerMercury Atmospheric and Surface Composition Spectrometer (MASCS)

The purpose of the Mercury Atmospheric and Surface Composition Spectrometer is to help determine what minerals are present on the surface of Mercury, and to help characterize the outermost layer of Mercury�s atmosphere. The MASCS is actually two instruments: an UltraViolet-Visible Spectrometer (UVVS) and a Visible-InfraRed Spectrograph (VIRS). Both instruments analyze sunlight that is reflected from the surface of Mercury. UVVS also examines light re-emitted from the planet�s tenuous atmosphere.

How it works

A spectrometer may sound foreign, but in fact it is similar in some respects to the human eye. If you look at an object and see color, your eyes and brain are working together to interpret the visible light that is reflected or emitted by that object. This is possible because different colors correspond to different wavelengths in the visible light. Similarly, a spectrometer collects light and separates it into its various wavelengths. By measuring the amount of light at each wavelength, the spectrometer can help us interpret what materials reflected or emitted that light. Thus, this instrument will help us understand what materials are present in the atmosphere and at the surface of Mercury.

A significant difference between the human eye and a spectrometer is that the human eye only detects visible light (a limited range of wavelengths) whereas a spectrometer can be designed to detect infrared and/or ultraviolet light as well. Infrared light has a longer wavelength than visible light, whereas ultraviolet radiation has a shorter wavelength than visible light.

a prism splitting light into its individual colors
A prism splits light into its individual colors.
( Image Credit: NASA)
In the MASCS, a single telescope focuses light coming from Mercury or its atmosphere so that it can be analyzed by both the UVVS and the VIRS. These instruments employ a device called a diffraction grating to disperse the light, acting like a prism to separate the colors or wavelengths. In the UVVS portion of MASCS, the light which has been spread out by the grating, then falls on an array of photomultiplier tubes, which are devices that convert the light energy at each selected wavelength to an electrical signal. The signal�s strength measures the amount of light at that wavelength, and this information can be sent back to Earth for interpretation. In VIRS, the spread-out spectrum falls on an array of detectors, each of which measures the light from a small range of wavelengths.

Interpretation of the data relies on the idea that the light detected by MESSENGER is a sort of fingerprint of the material from which it came. For example, iron can be found in different forms, and each form produces a unique spectral signature.

Spectral signatures are unique for different molecules or minerals, since these only absorb and reflect certain wavelengths of light. By looking at what wavelengths are absorbed and reflected by a material, scientists can determine what minerals are present on the surface of Mercury.

unique spectral signatures of iron forms
While this data was not collected by the same instrument, it reveals the unique spectral signature of the different forms of iron
from the surface of Mars. This data was collected using the Panoramic Camera Spectral Imager on the Mars exploration Rover, Spirit.
Image credit: NASA/JPL/Cornell

Contribution to our understanding of Mercury and beyond

The UltraViolet-Visible Spectrometer, for example, will tell us what the outer atmosphere (exosphere) of Mercury is composed of, and how it is structured. The Visible-InfraRed Spectrograph will tell us about some of the minerals that are present on the surface of Mercury.

a radar image of the north polar region of Mercury showing bright features that may be ice deposits
A radar image of the north polar region of Mercury,
showing bright features that could be ice deposits.
( Image Credit: J. Harmon, P. Perrilat, & M. Slade)
Ultimately, this information will be used to help us answer several important questions, such as:

  • How is the atmosphere on Mercury generated and maintained?
  • How are the surface composition and atmospheric composition of Mercury related?
  • What is the material at the poles of Mercury that reflects radar?
  • What are the common minerals on Mercury�s surface?

Other applications of this instrument

Similar instruments are used in chemistry laboratories, as well as on several NASA missions. For example, as early as 1969 one of the Mariner missions to Mars used an infrared spectrometer to learn about the Martian surface. The Near Earth Asteroid Rendezvous (NEAR) mission explored the geology of the asteroid 433 Eros. However, this mission first made sure the Near-Infrared Spectrometer was functioning properly by analyzing the surface and atmosphere of Antarctica:

antarctica and the NIS footprint NIS antarctic spectrum
An image of Antarctica from the NEAR spacecraft, alongside the spectrum taken using the
Near-Infrared Spectrometer onboard. And the spectrum reveals�water ice!! (Image Credit: NASA)

An ultraviolet spectrometer was used on the Galileo mission to Jupiter to study the ever-changing atmospheres of Jupiter and one of its moons, Io. Results indicate the presence of ammonia ice clouds in Jupiter�s turbulent atmosphere and active volcanoes contributing sulfur dioxide to Io�s atmosphere.

near-infrared image of jupiter’s great red spot
The Near-infrared Mapping Spectrometer on the Galileo spacecraft captured the
false-color image of Jupiter�s Great Red Spot, left, on June 26, 1996. The light blue color in the
upper left corner of the image indicates the presence of ammonia ice clouds. (Image Credit: NASA)

Infrared and Ultraviolet spectrometers are also used on Earth to study gases discharged from volcanoes, and in laboratories to learn which minerals are present in rocks, among other applications.

Working with the other instruments

Data from these instruments will be used in conjunction with data from the Gamma Ray and X-Ray Spectrometers as well as images from the Mercury Dual Imaging System to further define the composition of Mercury�s surface. Additionally, data from these instruments will help scientists learn about the impact of space weathering and the overall geologic history on Mercury�s surface.