**3. Viking and perchlorates**

A further support to a biological interpretation of the Viking LR experiment was given by R. Navarro-Gonzales [27]. In summary, a sample of a Mars-like soil of the driest core of the Atacama desert in Northern Chile (The Yungay Area), containing very low organic concentration (32 ppm), was subjected to a thermal volatilization process. The released gases and volatiles have been then measured by a GCMS similar to the Viking ones. At 500°C a clear emission of organic substances such as benzene, toluene, formic acid was observed. But when the same soil was heated at 500°C after the addition of 1% of Mg perchlorate, the organic substances mentioned were no longer observed, whereas release of CO2 and H2O and, amazingly, also of CH3Cl and CH2Cl2 was measured (**Figure 18**).

traces (0,02%) of other salt containing Cl, the quite abundant amount of Cl found by Vikings appears as a strong indication of the presence of perchlorates. The mechanism of Martian perchlorate production is still being debated. It has been suggested that production pathways for perchlorate on Mars are similar to Earth, primarily photochemically in the upper atmosphere via oxidation of chlorine by ozone [36]. But because of the low amount of Ozone in the Martian atmosphere, mechanisms involving surface components are probable [37]. For example, perchlorates may form from the radiolysis of surface component caused by galactic cosmic rays, causing a sublimation of chlorine oxide in atmosphere, where final oxidation to perchloric acid is performed by some sources of active Oxigen (i.e. O3 and/or CO2 photolysis) [38]. And in the presence of a suitable catalist such as TiO2 the strong Martian UV illumination could oxidize chloride ions to perchlorate also

The permanence of perchlorates (very soluble in water) on the martian soil is made possible by the strong ambient dryness: Mars lacks rains able to dissolve

2 Mg ClO ð Þ<sup>4</sup> <sup>2</sup> ! MgO þ MgCl2 þ 15*=*2 O2 þ 2Cl

The results of Phoenix and Atacama analyses, suggested to reconsider methods

The first chance for to this new approach occurred with the Curiosity mission (NASA, Mars Science Laboratory Press Kit, 2012), a rover of 900 kg that landed successfully on August 6, 2012 inside the Martian Gale crater (5.4°S 137.8°E) at a lower latitude than Viking (Cryse at 22,7°N and Utopia at 48,3°N), an ancient lake, with a layered mountain 5,000 m high in the center (the Mount Sharp). The task of Curiosity was to reach the mountain and to climb on it, in order to disclose the geological past of Mars, starting from the farter past (lower stratification)

(**Figure 19**). The most interesting soils were found right at the base of Mount Sharp, where Curiosity encountered a dangerous expanse of dark sand (Bagnold Dunes), a

On January 1, 2018 (sol 1992) near the southern edge of the Vera Ruin Ridge, the Mars Hand Lens Imager (MAHLI) camera on Curiosity movable arm, pointed out a cluster of millimetric dark, stick-shaped features whose origin is uncertain. One possibility is that they are erosion-resistant bits of dark material from mineral veins

But the morphological analogy with terrestrial fossil traces of life-substrate interactions is impressive [41]. Some studies even highlight occurrence, on Martian sediments, of widespread structures like the famous microspherules discovered by the Rovers Spirit and Opportunity, often organized into some higher-order settings (**Figure 22**). Such structures also occur on terrestrial stromatolites in a great variety

long ridge rich of hematite (Vera Rubin Ridge), a clay-bearing unit (Glen

Torridon), followed by Sulfur-rich uneven ground.

cutting through rocks in this area (**Figures 20** and **21**).

The logical interpretation of the Navarro Gonzales [27] results on the Atacama soil starts from the well known decomposition of Mg(ClO4)2 at

O2 and Cl react with organics compounds, releasing, on one side, H2O and CO2, and, on the other side, the chlorine compounds observed by the Viking

for searching carbon molecules on Mars, taking in account the significant risk

in aqueous solutions [39].

GCMS.

**149**

perchlorates for millions of years.

*New Insights into the Search for Life on Mars DOI: http://dx.doi.org/10.5772/intechopen.97176*

arising from the thermal methods.

**4. Curiosity and SAM results**

temperature > 400°C [40], with release of O2 and Cl:

According to Navarro Gonzales [27] the release CH3Cl and CH2Cl2 was ascribed to a reaction between perchlorate and organics. According to experiments on simulated Martian soil [28], the thermal action of perchlorate in the Vikings GCMS results should have substantiate by the detection of some chlorinated aromatics (such as chlorobenzene and chlorotoluene). Well, an accurate re-examination of the original, microfilm preserved, Viking GCMS data sets [29] found evidence for the presence of chlorobenzene in Viking Lander 2 (VL-2) data, at levels corresponding 0.08–1.0 ppb, in two sample heated to 350°C and 500°C. A surprising discovery that is also a demonstration of the presence of perchlorate in the Viking martian soil.

Unfortunately, the two Vikings were not able to search for perchlorates. But it is possible 'to read' the potential presence of these salts in some meaningful clues.

For example, the RXFS (X-Ray Fluorescence Spectrometer) on board the Viking lander was suitable to search for Cl (Chlorine) in martian soil, finding similar values: Viking 1 found 0,8% of Cl on the landing site of Cryse (22,7°N, 48,2° W) and Viking 2 found about 0,4% of Cl on the landing site of Utopia (48,3°N, 226°W) [30, 31]. Furthermore Pathfinder (1997) found up to 1% of Cl on Ares Valley (19,3°N, 33,6°W) [32], Spirit found about 0,5% of Cl inside the Gusev crater (14,6°N, 175,5°E) [33] and Opportunity found up to 1% of Cl on Meridiani Planum (1,9°S, 354,5°E) [34]. A more general investigation was made by the orbital spacecraft Odissey 2001, between June 2002 and April 2005. Its Gamma Ray Spectrometer (GRS), measured the equatorial and mid-latitude distribution of Cl at the near-surface of Mars, finding a not homogeneously concentration, with a mean value of 0.49 wt% Cl and variation up to a factor of 4 [35]. The kind of compound containing Cl should be investigated.

After the unexpected discovery of up to about 1% of Mg-perchlorate on the Martian polar soil (68.3°N, 127.0°W) performed by Phoenix Lander [24], with only

#### **Figure 18.**

*The dry soil of the Yungay Area (Northern Atacama), if heated up to 500°C with the external addition of perchlorates, shows the same behaviour of the Martian soil: disappearance of organic signals and release of light chloro-hydrocarbons.*

*New Insights into the Search for Life on Mars DOI: http://dx.doi.org/10.5772/intechopen.97176*

very low organic concentration (32 ppm), was subjected to a thermal volatilization process. The released gases and volatiles have been then measured by a GCMS similar to the Viking ones. At 500°C a clear emission of organic substances such as benzene, toluene, formic acid was observed. But when the same soil was heated at 500°C after the addition of 1% of Mg perchlorate, the organic substances mentioned were no longer observed, whereas release of CO2 and H2O and, amazingly, also of

According to Navarro Gonzales [27] the release CH3Cl and CH2Cl2 was ascribed to a reaction between perchlorate and organics. According to experiments on simulated Martian soil [28], the thermal action of perchlorate in the Vikings GCMS results should have substantiate by the detection of some chlorinated aromatics (such as chlorobenzene and chlorotoluene). Well, an accurate re-examination of the original, microfilm preserved, Viking GCMS data sets [29] found evidence for the presence of chlorobenzene in Viking Lander 2 (VL-2) data, at levels corresponding 0.08–1.0 ppb, in two sample heated to 350°C and 500°C. A surprising discovery that is also a demonstration of the presence of perchlorate in the Viking martian soil. Unfortunately, the two Vikings were not able to search for perchlorates. But it is possible 'to read' the potential presence of these salts in some meaningful clues. For example, the RXFS (X-Ray Fluorescence Spectrometer) on board the Viking lander was suitable to search for Cl (Chlorine) in martian soil, finding similar values: Viking 1 found 0,8% of Cl on the landing site of Cryse (22,7°N, 48,2° W) and Viking 2 found about 0,4% of Cl on the landing site of Utopia (48,3°N, 226°W) [30, 31]. Furthermore Pathfinder (1997) found up to 1% of Cl on Ares Valley (19,3°N, 33,6°W) [32], Spirit found about 0,5% of Cl inside the Gusev crater (14,6°N, 175,5°E) [33] and Opportunity found up to 1% of Cl on Meridiani Planum (1,9°S, 354,5°E) [34]. A more general investigation was made by the orbital spacecraft Odissey 2001, between June 2002 and April 2005. Its Gamma Ray Spectrometer (GRS), measured the equatorial and mid-latitude distribution of Cl at the near-surface of Mars, finding a not homogeneously concentration, with a mean value of 0.49 wt% Cl and variation up to a factor of 4 [35]. The kind of compound containing Cl should be investigated. After the unexpected discovery of up to about 1% of Mg-perchlorate on the Martian polar soil (68.3°N, 127.0°W) performed by Phoenix Lander [24], with only

*The dry soil of the Yungay Area (Northern Atacama), if heated up to 500°C with the external addition of perchlorates, shows the same behaviour of the Martian soil: disappearance of organic signals and release of light*

CH3Cl and CH2Cl2 was measured (**Figure 18**).

*Solar System Planets and Exoplanets*

**Figure 18.**

**148**

*chloro-hydrocarbons.*

traces (0,02%) of other salt containing Cl, the quite abundant amount of Cl found by Vikings appears as a strong indication of the presence of perchlorates. The mechanism of Martian perchlorate production is still being debated. It has been suggested that production pathways for perchlorate on Mars are similar to Earth, primarily photochemically in the upper atmosphere via oxidation of chlorine by ozone [36]. But because of the low amount of Ozone in the Martian atmosphere, mechanisms involving surface components are probable [37]. For example, perchlorates may form from the radiolysis of surface component caused by galactic cosmic rays, causing a sublimation of chlorine oxide in atmosphere, where final oxidation to perchloric acid is performed by some sources of active Oxigen (i.e. O3 and/or CO2 photolysis) [38]. And in the presence of a suitable catalist such as TiO2 the strong Martian UV illumination could oxidize chloride ions to perchlorate also in aqueous solutions [39].

The permanence of perchlorates (very soluble in water) on the martian soil is made possible by the strong ambient dryness: Mars lacks rains able to dissolve perchlorates for millions of years.

The logical interpretation of the Navarro Gonzales [27] results on the Atacama soil starts from the well known decomposition of Mg(ClO4)2 at temperature > 400°C [40], with release of O2 and Cl:

$$\mathsf{2Mg} \ (\mathsf{ClO}\_4)\_2 \to \mathsf{MgO} + \mathsf{MgCl}\_2 + \mathsf{15}/2\ \mathsf{O}\_2 + \mathsf{2Cl}$$

O2 and Cl react with organics compounds, releasing, on one side, H2O and CO2, and, on the other side, the chlorine compounds observed by the Viking GCMS.

The results of Phoenix and Atacama analyses, suggested to reconsider methods for searching carbon molecules on Mars, taking in account the significant risk arising from the thermal methods.
