The Viking GC/MS: The Seek for Organic Compounds on Mars

The Viking GC/MS program, conducted during NASA‘s Viking missions in 1976, was the first direct attempt to search for organic molecules on another planet. This program marks a pivotal moment in Mars exploration.

Both Viking 1 and Viking 2, the first successful Mars landers, were equipped with Gas Chromatograph/Mass Spectrometer (GC/MS) instruments to carry out this task.

These identical landers conducted four types of biological experiments, including the GC/MS tests, at two different sites on Mars—Viking 1 near the equator and Viking 2 further north.

The GC/MS experiment was designed to detect organic compounds, which are the fundamental keys of life. In this process, Martian soil samples were heated to vaporize any organic molecules present, and the resulting gases were analyzed by the gas chromatograph and mass spectrometer.

The aim was to identify any biological material in the Martian soil by separating volatile elements with the gas chromatograph and determining their composition with the mass spectrometer.

Image-1. Viking. (Image Credit: NASA).

Background of the Viking Missions

The Viking program was initiated in response to growing interest in Mars, fueled by previous flyby missions like Mariner 4 in 1965, which provided the first close-up images of the Martian surface.

Planning for the Viking missions began in the late 1960s. The mission’s primary purposes were to search for biosignatures of life.

Viking 1 was launched on August 20, 1975, followed by Viking 2 on September 9, 1975. Both spacecraft reached Mars in mid-1976.

The Viking program consisted of two spacecraft, Viking 1 and Viking 2, each composed of an orbiter and a lander.

The orbiter’s role was to photograph the Martian surface. The lander was equipped with scientific instruments to carry out experiments on the ground.

The Viking landers were equipped with several scientific instruments, including the Gas Chromatograph/Mass Spectrometer (GC/MS), to analyze the Martian surface and atmosphere.

Image-2. NASA’s Curiosity rover. (Image Credit: NASA/GSFC).

What Is Organic Matter?

Organic molecules consist of a wide variety of compounds made primarily of carbon and usually include hydrogen and oxygen atoms. They can also contain other elements, such as nitrogen, phosphorus, and sulfur.

On Earth, organic matter is generally associated with life processes, including living organisms, their remains, and the byproducts of life.

The presence of these specific molecules is considered to be a potential biosignature. it raises the possibility that life could exist or could have existed if the right conditions were present. A substance or structure that could be evidence of past life but may also have been produced without the presence of life.

Image-3. Viking, Gas Chromatograph Mass Spectrometer. (Image Credit: National Air and Space Museum).

How the GC/MS Works?

A gas chromatograph/mass spectrometer (GC/MS) is a device that separates vapor components chemically via a gas chromatograph and then feeds the result into a mass spectrometer, which measures the molecular weight of each chemical.

The GCMS was used to analyze the components of untreated Martian soil, and particularly those components that are released as the soil is heated to different temperatures.

Gas Chromatography:

Gas Chromatography (GC) technique separates the components of a sample. The sample, often in liquid or solid form, is injected into the GC system where it is vaporized.

Different compounds travel through this column at different speeds based on their chemical properties. These different chemical properties -different interactions with the stationary phase- allow for their separation. The GC unit in the Viking landers was designed to separate complex mixtures of gases into individual components.

The soil samples collected by the robotic arm were placed in an oven and heated to temperatures up to 500°C. This heating process vaporized any potential organic compounds in the soil.

The vaporized gases moved through the column, different compounds separated based on their volatility and interactions with the column’s stationary phase.

Mass Spectrometry (MS):

After separation, the components enter the mass spectrometer, where they are ionized, fragmented, and then detected based on their mass-to-charge ratio. This allows scientists to identify the chemical structure of each compound.

The mass spectrum acts like a fingerprint for each compound. The fragments were then sorted based on their mass-to-charge ratio, and a detector recorded the abundance of each fragment. This allows scientists to determine the identity of the original molecules.

Results of the Viking GC/MS on Mars

The Viking GC/MS was pioneering in its approach and set the stage for subsequent missions to Mars, like the Mars Science Laboratory’s Curiosity rover in 2011, which continued the search for organic molecules and signs of past life.

The GCMS measured no significant amount of organic molecules in the Martian soil. The Viking GC/MS did not find definitive evidence of organic molecules in the Martian soil.

The Viking GC/MS detected trace amounts of chlorinated hydrocarbons in the Martian soil. Chlorohydrocarbons were found at landing sites 1 and 2. They were dismissed at the time as terrestrial contaminants, even though they were not found at the same levels in blank runs.

Only water at 0.1–1.0 wt% was detected, with traces of chloromethane at 15 ppb, at Viking landing site 1. Water at 0.05–1.0 wt% and carbon dioxide at 50–700 ppm, with traces of dichloromethane at 0.04–40 ppb, at Viking landing site 2.

Perchlorates are well-known as powerful oxidizing compounds that combust organics, but their presence in Martian soils was not thought in the Viking GC/MS 1976.

Then Nasa’s 2008 Phoenix mission to Mars unexpectedly detected perchlorate salts at the northern polar landing site.

Decades later, the discovery of perchlorates (salts containing the ClO₄⁻ ion) in Martian soil by the Phoenix lander in 2008 prompted a reevaluation of the Viking data.

Despite this, the Viking missions did not find clear evidence of organic molecules. This caused continued debate and further missions to study the Martian environment.

Recent re-evaluations suggest that these might be breakdown products of Martian organics, possibly influenced by perchlorates in the soil.

According to a 2010 NASA press release: “The only organic chemicals identified when the Viking landers heated samples of Martian soil were chloromethane and dichloromethane — chlorine compounds interpreted at the time as likely contaminants from cleaning fluids.”

However, the 2010 NASA press release also noted that: “One reason the chlorinated organics found by Viking were interpreted as contaminants from Earth was that the ratio of two isotopes of chlorine in them matched the three-to-one ratio for those isotopes on Earth.

The ratio for them on Mars has not been clearly determined yet. If it is found to be much different than Earth’s, that would support the 1970s interpretation.”

Image-4. The perchlorate Martian mystery. (Image Credit: NASA/JPL-Caltech/MSSS).

Perchlorates and Their Role:

Perchlorates are salts that contain the ClO₄⁻ ion, and they were discovered in Martian soil by the Phoenix lander in 2008. These compounds are reactive, especially when heated, and can break down organic molecules.

This suggests that the Viking landers may have actually detected Martian organics that were transformed by perchlorates during the heating process.

Perchlorate was detected in Martian soil at the level of ~0.6% by weight.[19][20] It was shown that at the Phoenix landing site it was present as a mixture of 60% Ca(ClO4)2 and 40% Mg(ClO4)2.

These salts, formed from perchlorates, act as antifreeze and substantially lower the freezing point of water.

Based on the temperature and pressure conditions on present-day Mars at the Phoenix lander site, conditions would allow a perchlorate salt solution to be stable in liquid form for a few hours each day during the summer.

In this article, We have mentioned the Viking Mission of NASA as a MoEP ARK Team. In the next articles, more astrobiology contents will come. Keep following us!