Mercury 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.
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 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.
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 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:
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:
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.
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.
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.
