Gain Controller, Mass Spectrometer, Gas Chromatograph, Project Viking, Prototype

This is a prototype of the Gas Chromatograph-Mass Spectrometer (GCMS) used on Project Viking. Developed and built by Litton Systems, Inc., it is an example of the difficult history of the development of the GCMS in the early 1970s. This object was used for many tests and aided in planning for modifications to the flight instruments. Its design reflects problems refining the instrument's size and weight.

The GCMS experiment for each of the two Viking Landers, which landed on Mars in the early 1970s, were the key instruments in proving that other Viking experiments were not detecting life. It was designed to measure the amount of organic molecules in the Martian soil. Results of the GCMS work allowed scientists to determine such molecules did not exist.

This artifact was transferred to NASM by the NASA Jet Propulsion Laboratory in 2004.

Surface Composition

To determine the composition of the atmosphere, and whether organic molecules exist in the surface samples, a Gas Chromatograph Mass Spectrometer measured the atomic composition of gas samples from heated soil and the atmosphere. No organic molecules were detected at either landing site, but the abundance of the gas argon (36AR) was found to be less than that expected. This difference suggests that during the early evolution of the planet, the amount of gas released to the atmosphere of Mars was less than that released to the atmosphere of the early Earth.

The composition of heavier elements, those that are common in rocks and soils, is determined by means of an X-ray Fluorescence Spectrometer. Samples of Mars are dropped into the instrument in the Lander body, where they are exposed to high-energy x-rays. Each element then produces its own characteristic x-rays, which are counted and recorded. Following the analysis, the sample is dropped out of the bottom of the test container so a new sample can be measured.

Analysis of the surface soil indicates that both landing sites are similar in composition and primarily composed of the elements silicon and iron. The sulfur content is unexpectedly high, and might be caused by water-soluble minerals deposited on the surface. Lander soils could be derived from weathering of an iron-rich igneous rock, such as basalt. Consistent with these analyses, magnetic particles were photographed clinging to the magnets on the sampling arm and on the camera reference chart.