**4. Curiosity and SAM results**

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 long ridge rich of hematite (Vera Rubin Ridge), a clay-bearing unit (Glen Torridon), followed by Sulfur-rich uneven ground.

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

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

**Figure 19.** *The path of Curiosity inside the Gale crater, to reach the base of Mount Sharp.*

#### **Figure 20.**

*December 13, 2017 (sol 1903): Curiosity near the Vera Rubin Ridge, a formation very rich of hematite.*

of microscopic structures, such as voids, gas domes and layer deformations of microbial mats [42].

SAM (Sample Analysis at Mars) is a suite of instruments aimed at analyzing of soil samples on board of Curiosity (**Figure 23**).

It includes an improved and more sensitive (up to 100 times) version of the Viking GC MS [43] and a laser infrared spectrometer (TLS) [44] able to analyse any gaseous substance from both Martian atmosphere and GC–MS, with a sensitivity of 1 ppb (part per billion). The SAM works by accepting drilled or scooped Martian grit into a tiny cup made of quartz, that can be cooked in an oven up to 1100°C. Tiny puffs of helium gas move the gases from the sample cup into a MS (Mass Spectrometer), that sift through the resulting fumes for molecular signatures, directly (EGA, Evolved Gas Analysis) or after a previous separation inside one of 6 column GC (Gas Chromatographic) (**Figure 24**). There are 74 cups in a carousel: 59

are quartz tubes slated for "dry" chemistry, 9 are solvent cups, sealed with foil, contain solvents for 'wet' chemistry to tease out organic molecules, like amino acids and degraded fatty acids, that would otherwise resist vaporization; the last 6 are

*Examples of mesostructural parallels with occurrence of spherical bodies having similar shape and structure. On Mars, 'blueberries' could assume polycentric polispherules or concentric structures. Such parallels occur also for living colony of cyanobacteria (frame II), as polispherule and concentric structures and for stromatolites (the*

*January 1, 2018 (sol 1992): these enigmatic dark, stick-shaped features taken from the MAHALI camera on*

*board of Curiosity look alike terrestrial fossils of the Ordovician period.*

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

Among other capacities, the TLS [44], detecting the IR absorption band of CH4 at 3,27 micron, was aimed at confirming the existence and the seasonal cycle of methane discovered by terrestrial telescopes [45] and possibly confirmed by PFS

calibration cups (**Figure 25**).

*knot structure in the frame III.*

**Figure 21.**

**Figure 22.**

**151**

#### **Figure 21.**

*January 1, 2018 (sol 1992): these enigmatic dark, stick-shaped features taken from the MAHALI camera on board of Curiosity look alike terrestrial fossils of the Ordovician period.*

#### **Figure 22.**

of microscopic structures, such as voids, gas domes and layer deformations of

*December 13, 2017 (sol 1903): Curiosity near the Vera Rubin Ridge, a formation very rich of hematite.*

SAM (Sample Analysis at Mars) is a suite of instruments aimed at analyzing of

It includes an improved and more sensitive (up to 100 times) version of the Viking GC MS [43] and a laser infrared spectrometer (TLS) [44] able to analyse any gaseous substance from both Martian atmosphere and GC–MS, with a sensitivity of 1 ppb (part per billion). The SAM works by accepting drilled or scooped Martian grit into a tiny cup made of quartz, that can be cooked in an oven up to 1100°C. Tiny puffs of helium gas move the gases from the sample cup into a MS (Mass Spectrometer), that sift through the resulting fumes for molecular signatures, directly (EGA, Evolved Gas Analysis) or after a previous separation inside one of 6 column GC (Gas Chromatographic) (**Figure 24**). There are 74 cups in a carousel: 59

microbial mats [42].

**Figure 20.**

**150**

**Figure 19.**

*Solar System Planets and Exoplanets*

soil samples on board of Curiosity (**Figure 23**).

*The path of Curiosity inside the Gale crater, to reach the base of Mount Sharp.*

*Examples of mesostructural parallels with occurrence of spherical bodies having similar shape and structure. On Mars, 'blueberries' could assume polycentric polispherules or concentric structures. Such parallels occur also for living colony of cyanobacteria (frame II), as polispherule and concentric structures and for stromatolites (the knot structure in the frame III.*

are quartz tubes slated for "dry" chemistry, 9 are solvent cups, sealed with foil, contain solvents for 'wet' chemistry to tease out organic molecules, like amino acids and degraded fatty acids, that would otherwise resist vaporization; the last 6 are calibration cups (**Figure 25**).

Among other capacities, the TLS [44], detecting the IR absorption band of CH4 at 3,27 micron, was aimed at confirming the existence and the seasonal cycle of methane discovered by terrestrial telescopes [45] and possibly confirmed by PFS

#### **Figure 23.**

*The suite of instruments of SAM (Sample Analysis at Mars) laboratory on board of Curiosity.*

spectromenter on board of Mars Express [46]. The task of TLS was to continue the search for methane in order to establish its source (geological or biological).

*Seasonal variations of Martian methane, detected by the SAM-TLS spectrometer, during 55 months (about three Mars years from March 17 2014 to March 21, 2017.Potential methane sources include methanogenesis by microbes, ultraviolet degradation of organics, or water-rock chemistry. The methane could be later destroyed by atmospheric photochemistry or surface reactions, as examples. Seasons refer to the northern hemisphere.*

*The Carousel of SAM, called the SMS (Sample Manipulation System). It contains 74 cups, dedicated to receiving solid samples collected by the Curiosity rover. The 74 sample cups are separated into three categories: 59 solid sample quartz cups, 9 foil topped metal cups for wet chemistry experiments (7 with MTBSTFA, 2 with*

**Figure 25.**

**Figure 26.**

**153**

*TMAH), and 6 foil topped cups of reference samples.*

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

Really, TLS detected methane many times over the course of the mission, though with a very strange behaviour. Background levels of the gas seem to rise and fall seasonally (0,24–0,65 ppbv, parts per billion units by volume) [47] (**Figure 26**). The highest methane levels do appear just after the warmest time of the year, suggesting that heat spreading downward allows more of the gas to be released.

#### **Figure 24.**

*Inside the SAM lab., gases released by a sample of Martian soil heated up to 1000°C can be sent to a Mass Spectrometer (MS) directly (EGA-MS, Evolved Gas Analysis) or passing before though Gas-chromatographic column (GCMS).*

#### **Figure 25.**

**Figure 23.**

*Solar System Planets and Exoplanets*

**Figure 24.**

**152**

*column (GCMS).*

*The suite of instruments of SAM (Sample Analysis at Mars) laboratory on board of Curiosity.*

*Inside the SAM lab., gases released by a sample of Martian soil heated up to 1000°C can be sent to a Mass Spectrometer (MS) directly (EGA-MS, Evolved Gas Analysis) or passing before though Gas-chromatographic* *The Carousel of SAM, called the SMS (Sample Manipulation System). It contains 74 cups, dedicated to receiving solid samples collected by the Curiosity rover. The 74 sample cups are separated into three categories: 59 solid sample quartz cups, 9 foil topped metal cups for wet chemistry experiments (7 with MTBSTFA, 2 with TMAH), and 6 foil topped cups of reference samples.*

spectromenter on board of Mars Express [46]. The task of TLS was to continue the search for methane in order to establish its source (geological or biological).

Really, TLS detected methane many times over the course of the mission, though with a very strange behaviour. Background levels of the gas seem to rise and fall seasonally (0,24–0,65 ppbv, parts per billion units by volume) [47] (**Figure 26**).

The highest methane levels do appear just after the warmest time of the year, suggesting that heat spreading downward allows more of the gas to be released.

#### **Figure 26.**

*Seasonal variations of Martian methane, detected by the SAM-TLS spectrometer, during 55 months (about three Mars years from March 17 2014 to March 21, 2017.Potential methane sources include methanogenesis by microbes, ultraviolet degradation of organics, or water-rock chemistry. The methane could be later destroyed by atmospheric photochemistry or surface reactions, as examples. Seasons refer to the northern hemisphere.*

Finding methane in Mars's atmosphere is intriguing because chemical reactions should destroy the gas after about 300 years. So its presence today suggests that something on the planet is still sending the gas into the atmosphere. The source could be geological, such as reactions between certain types of rock and water (basaltic serpentinization) or could be linked to ancient methane trapped in clathrate hydrates; more intriguingly, the warmest season could 'awaken' buried microbes or other forms of life, taking in account that most of the methane in Earth's atmosphere comes from living processes. But a recent statistical analysis [48] casts doubt on the hypothesis of "seasonal variability" in Mars'surface methane, finding that it is unsupported by the Curiosity TLS data. This is because the data are too sparse over too limited timespan, to favor a seasonally cyclic explanation of the data over alternative hypotheses of stochastic variation or variation with other periods.

TLS detected also episodically increases ('spike') of Martian methane [49]: for example on June 16, 2013 and on early January 2014 readings averaged ten time the background level (6–8 ppbv). The largest concentration of methane detected in situ by the Curiosity reached a spike to 21 ppbv, on June 20, 2019, dropping quickly over a few days (**Figure 27**).

which includes the strongest fundamental absorption bands for hydrocarbons such as CH4, in particular the ν3 asymmetric stretching band on which all the previous

*On June 13, 2013, the PFS spectrometer on board of Mars Express observed a methane emission over the fractured terrain of Medusae Fossae, some hours before a spike of methane detected inside the Gale crater by the TLS-SAM instrument. Geological methane carried towards the Gale crater by the prevailing winds?*

Until the end of 2020 the SAM-GCMS made more than twenty complete ana-

Inside the Gale crater Curiosity discovered for the first time, Martian organic molecules, just after a few attempts (Rocknest, John Klein, Cumberland at Yellow-

Yellowknife Bay mudstone is thought to contain sediments transported by

sandy terrain of Rocknest, located about 550 meters away the landing site. The APXS instrument (Alpha Particle-X rays spectrometer) [52] detected on Rocknest a little amount of S and Cl [53]. The sandy texture of the soil was suitable to be easily transferred inside the SAM. Under the heating of the sample up to 800°C, many kinds of gaseous substances were released [54]. The release of molecular Oxigen (O2) at 300–400°C (**Figure 31**) was very important: together with the presence of

Between sol 56 and 100 (October 2 to November 16, 2012) Curiosity reached the

detections were made.

**Figure 28.**

**Figure 29.**

**155**

lyses on Gale crater soil (**Figure 29**).

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

knife Bay, not far from the landing site) (**Figure 30**).

fluvial and deltaic processes from the crater rim area to the north.

*A summary of all drill sites made by Curiosity at Gale Crater up the end of 2020.*

The PFS spectrometer of Mars Express found a possible geological origin of this n usual pattern [50]. Indeed, in a re-examination of archive data, PFS, on June 16, 2013, observed an elevated spot level (15.5 2.5 ppbv) of methane, from a nearby area called Medusae Fossae, located about 500 km east of Gale crater. The Mars Express observation was made 20 hours before the methane spike of 5.78 2.27 ppbv reported by TLS-SAM. Being Medusae Fossae a fractured and likely volcanic in origin, it is possible that a therein geological emission of methane has been carried by the prevailing winds towards the Gale crater (**Figure 28**).

Highly sensitive measurements of the atmosphere of Mars performed by the ESA-Roscosmos ExoMars TGO (Trace Gas Orbiter) from April to August 2018 made the problem of Martian methane even more enigmatic [51]. No trace of methane was indeed found by two instrument suites onboard TGO designed to perform such measurements: ACS (the Atmospheric Chemistry Suite) and NOMAD (Nadir and Occultation for Mars Discovery) that cover the 3.3 μm spectral range,

#### **Figure 27.**

*TLS-SAM methane measurements at Gale crater over an 4.5 Earth years (56 months) period (from 26 October 2012 to 27 May 2017), taken during the rover's journey of 16.5 km over highly varied terrain.*

#### **Figure 28.**

Finding methane in Mars's atmosphere is intriguing because chemical reactions should destroy the gas after about 300 years. So its presence today suggests that something on the planet is still sending the gas into the atmosphere. The source could be geological, such as reactions between certain types of rock and water (basaltic serpentinization) or could be linked to ancient methane trapped in clathrate hydrates; more intriguingly, the warmest season could 'awaken' buried microbes or other forms of life, taking in account that most of the methane in Earth's atmosphere comes from living processes. But a recent statistical analysis [48] casts doubt on the hypothesis of "seasonal variability" in Mars'surface methane, finding that it is unsupported by the Curiosity TLS data. This is because the data are too sparse over too limited timespan, to favor a seasonally cyclic explanation of the data over alternative hypotheses of stochastic variation or

TLS detected also episodically increases ('spike') of Martian methane [49]: for example on June 16, 2013 and on early January 2014 readings averaged ten time the background level (6–8 ppbv). The largest concentration of methane detected in situ by the Curiosity reached a spike to 21 ppbv, on June 20, 2019, dropping quickly over

The PFS spectrometer of Mars Express found a possible geological origin of this n usual pattern [50]. Indeed, in a re-examination of archive data, PFS, on June 16, 2013, observed an elevated spot level (15.5 2.5 ppbv) of methane, from a nearby area called Medusae Fossae, located about 500 km east of Gale crater. The Mars Express observation was made 20 hours before the methane spike of 5.78 2.27 ppbv reported by TLS-SAM. Being Medusae Fossae a fractured and likely volcanic in origin, it is possible that a therein geological emission of methane has been

Highly sensitive measurements of the atmosphere of Mars performed by the ESA-Roscosmos ExoMars TGO (Trace Gas Orbiter) from April to August 2018 made the problem of Martian methane even more enigmatic [51]. No trace of methane was indeed found by two instrument suites onboard TGO designed to perform such measurements: ACS (the Atmospheric Chemistry Suite) and NOMAD (Nadir and Occultation for Mars Discovery) that cover the 3.3 μm spectral range,

*TLS-SAM methane measurements at Gale crater over an 4.5 Earth years (56 months) period (from 26 October 2012 to 27 May 2017), taken during the rover's journey of 16.5 km over highly varied terrain.*

carried by the prevailing winds towards the Gale crater (**Figure 28**).

variation with other periods.

*Solar System Planets and Exoplanets*

a few days (**Figure 27**).

**Figure 27.**

**154**

*On June 13, 2013, the PFS spectrometer on board of Mars Express observed a methane emission over the fractured terrain of Medusae Fossae, some hours before a spike of methane detected inside the Gale crater by the TLS-SAM instrument. Geological methane carried towards the Gale crater by the prevailing winds?*

which includes the strongest fundamental absorption bands for hydrocarbons such as CH4, in particular the ν3 asymmetric stretching band on which all the previous detections were made.

Until the end of 2020 the SAM-GCMS made more than twenty complete analyses on Gale crater soil (**Figure 29**).

Inside the Gale crater Curiosity discovered for the first time, Martian organic molecules, just after a few attempts (Rocknest, John Klein, Cumberland at Yellowknife Bay, not far from the landing site) (**Figure 30**).

Yellowknife Bay mudstone is thought to contain sediments transported by fluvial and deltaic processes from the crater rim area to the north.

Between sol 56 and 100 (October 2 to November 16, 2012) Curiosity reached the sandy terrain of Rocknest, located about 550 meters away the landing site. The APXS instrument (Alpha Particle-X rays spectrometer) [52] detected on Rocknest a little amount of S and Cl [53]. The sandy texture of the soil was suitable to be easily transferred inside the SAM. Under the heating of the sample up to 800°C, many kinds of gaseous substances were released [54]. The release of molecular Oxigen (O2) at 300–400°C (**Figure 31**) was very important: together with the presence of

#### **Figure 30.**

*December 24, 2012 (sol 137): this mosaic of images from Curiosity-Mastcam shows the rocks of Yellowknife Bay formation, that record superimposed ancient lake and stream deposits that offered past environmental conditions favorable for microbial life. Rocks here were exposed about 70 million years ago by removal of overlying layers due to erosion by the wind. Yellowknife Bay mudstone is thought to contain sediments transported by fluvial and deltaic processes from the crater rim area to the north.*

But alternative hypotheses could have been given. The water and carbon dioxide seen by SAM could be breakdown products of organic substances under the action of perchlorates. This claim results from another discovery of GCMS on board SAM: the detection of simple chlorinated molecules, such as CH3Cl and minor amount of CH2Cl2 and CHCl3 [25]. At the end of February 2013 the SAM made a second series of analyses on a powdered sample of a sedimentary terrain named John Klein (**Figure 33**), located about 50 meters away from Rocknest, confirming results of first analysis, i.e. emission of CO2 and H2O, of O2 over 250°C (probably generated

*Thermal decomposition of perchlorates measured by the Author on a TGA (Thermal Gravimetric Analysis) instrument. Each perchlorate shows a specific temperature of decomposition with release of Oxygen.*

Therefore, the SAM and Viking GCMS results look strikingly similar, in the sense that a sufficient amount of perchlorates could mask occurrence of organics.

*February 2013: results by SAM-Curiosity from a powdered material drilled into the John Klein sedimentary*

*rock. On top the EGA evolved gases, on bottom some CGMS light chloro-derivatives.*

by perchlorates dissociation), and release of CH3Cl + CH3Cl2 [55].

**Figure 32.**

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

**Figure 33.**

**157**

#### **Figure 31.**

*November 2012 (sol 93–117): results from analysis of Rocknest Aeolian deposit by SAM-Curiosity. On top the EGA evolved gases, on bottom some CGMS light chloro-derivatives.*

Cl, this emission is a suggestion of Ca (ClO4)2 (Calcium perchlorate), a salt that decomposes under heat just to this temperature.

Laboratory–based TGA (Thermal Gravimetrical Analysis, performed by the Author with a Perkin-Elmer TGA 7 instrument) on synthetic perchlorates shows clearly that the Calcium perchlorate starts to release molecular oxigen at 350°C, leaving a main residue of Calcium chloride (CaCl2) (**Figure 32**). Therefore, after the discovery of perchlorate at high latitude by Phoenix, SAM demonstrated an occurrence of perchlorate also at equatorial latitude: so its occurrence also at mid-latitude (i.e. Viking landing sites) comes out strengthened.

Actually, between 200 and 500°C, the soil of Rocknest released water and two peaks of CO2 (i.e. two releases at two different temperatures). The origin of this water and Carbon dioxide is doubtful. Being released at more than 200°C, the water cannot be free, but bound to soil minerals as water of crystallization. In addition, a lab simulation shows that the two peaks of CO2 could arise from the thermal decomposition of Mg and Fe carbonate [54].

**Figure 32.** *Thermal decomposition of perchlorates measured by the Author on a TGA (Thermal Gravimetric Analysis) instrument. Each perchlorate shows a specific temperature of decomposition with release of Oxygen.*

But alternative hypotheses could have been given. The water and carbon dioxide seen by SAM could be breakdown products of organic substances under the action of perchlorates. This claim results from another discovery of GCMS on board SAM: the detection of simple chlorinated molecules, such as CH3Cl and minor amount of CH2Cl2 and CHCl3 [25]. At the end of February 2013 the SAM made a second series of analyses on a powdered sample of a sedimentary terrain named John Klein (**Figure 33**), located about 50 meters away from Rocknest, confirming results of first analysis, i.e. emission of CO2 and H2O, of O2 over 250°C (probably generated by perchlorates dissociation), and release of CH3Cl + CH3Cl2 [55].

Therefore, the SAM and Viking GCMS results look strikingly similar, in the sense that a sufficient amount of perchlorates could mask occurrence of organics.

#### **Figure 33.**

*February 2013: results by SAM-Curiosity from a powdered material drilled into the John Klein sedimentary rock. On top the EGA evolved gases, on bottom some CGMS light chloro-derivatives.*

Cl, this emission is a suggestion of Ca (ClO4)2 (Calcium perchlorate), a salt that

*December 24, 2012 (sol 137): this mosaic of images from Curiosity-Mastcam shows the rocks of Yellowknife Bay formation, that record superimposed ancient lake and stream deposits that offered past environmental conditions favorable for microbial life. Rocks here were exposed about 70 million years ago by removal of overlying layers due to erosion by the wind. Yellowknife Bay mudstone is thought to contain sediments*

*transported by fluvial and deltaic processes from the crater rim area to the north.*

Laboratory–based TGA (Thermal Gravimetrical Analysis, performed by the Author with a Perkin-Elmer TGA 7 instrument) on synthetic perchlorates shows clearly that the Calcium perchlorate starts to release molecular oxigen at 350°C, leaving a main residue of Calcium chloride (CaCl2) (**Figure 32**). Therefore, after the discovery of perchlorate at high latitude by Phoenix, SAM demonstrated an occurrence of perchlorate also at equatorial latitude: so its occurrence also at mid-latitude

*November 2012 (sol 93–117): results from analysis of Rocknest Aeolian deposit by SAM-Curiosity. On top the*

Actually, between 200 and 500°C, the soil of Rocknest released water and two peaks of CO2 (i.e. two releases at two different temperatures). The origin of this water and Carbon dioxide is doubtful. Being released at more than 200°C, the water cannot be free, but bound to soil minerals as water of crystallization. In addition, a lab simulation shows that the two peaks of CO2 could arise from the thermal

decomposes under heat just to this temperature.

*EGA evolved gases, on bottom some CGMS light chloro-derivatives.*

**Figure 30.**

*Solar System Planets and Exoplanets*

**Figure 31.**

**156**

(i.e. Viking landing sites) comes out strengthened.

decomposition of Mg and Fe carbonate [54].

After many months of stop due to a serious pollution problem (see later), the SAM team started again its analytical work, on a soil sample of the site of Cumberland that was taken an year before, on May 2013 not far from John Klein. The SAM results were crucial [56]: aside from the usual light Chloro-derivatives, many chlorinated aromatics were detected [57] suggesting that they could be derived from organic molecules present in the mudstone (from bacteria or from a meteoric extract): between them also an abundant release (about 250 ppb) of Chlorobenzene was detected (**Figure 34**), so reaching for an other resemblance to the Viking results, in which Chloro-benzene (as mentioned before) was found after a recent accurate re-examination of the original GCMS data [29].

One of the most extraordinary SAM discovery was made at Pahrump Hills (at the base of3.5-billion-year-old Murray mudstone), located at the lowermost portion of the Sharp Mons (Gale Crater central mound), about 6–7 km southwest of Yellowknife Bay. This 3.5-billion-year-old Gale lake environment is expected to have been ideal settings for concentrating and preserving organic matter [58]. Two samples were drilled: Confidence Hills on sol 759 (24 Sep 2014), and Mojave on sol 882 (29 Jan 2015) (**Figure 35**). Confidence Hills soil was rich of hematite, Mojave soil was rich of jarosite, evidence of ancient passage of water. Because ultraviolet radiation and oxidizing compounds in the Martian soil would destroy any compounds exposed at the surface, Curiosity's scientists used a robotic drill to penetrate several centimetres into the mudstone.

To unlock organic molecules from the samples, the oven baked them to temperatures of between 600°C and 860°C and fed the resulting fumes to the Mass Spectrometer, which identified a welter of closely related organic signals reflecting dozens or hundreds of types of small carbon molecules, such as aromatic rings and short aliphatic chains [59]. Abundant sulfur-bearing carbon rings called thiophenes, were also detected and identified in the GC (**Figure 36**).

The mass patterns looked like those generated on Earth by kerogen (aromatic rings, short aliphatic chains, sulphur containing molecules), a goopy high molecular material that is formed when geologic forces compress, during million of years, the ancient remains of algae and similar critters. Kerogen is sometimes found with sulfur, which helps preserve it across billions of years; the Curiosity scientists think the sulfur compounds in their samples also explain the longevity of the Mars compounds. At the moment, it is impossible to say whether ancient life explains the Martian organics. The signal, being found at the base of a lake 3,5 billion years old, when Mars environment was warm and wet, could be a potential catchment for the presence on Mars of archea bacteria in primordial epoch, possibly still present today

*SAM-EGA evolved gases from Majave drilled material: sulfur-bearing carbon rings, short aliphatic chains and*

*aromatic rings are typical decomposition products of keragenic material.*

*Confidence Hills and Mojave drill sites, at Pahrump Hills location, were SAM made the main discovery of*

**Figure 35.**

**Figure 36.**

**159**

*possible keragenic material.*

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

#### **Figure 34.**

*December 2014: results by SAM-Curiosity from a powdered material drilled into the Cumberland sedimentary rock. Very important (bottom), between the GCMS evolved chloro-derivatives, the presence of chloro-benzene, a byproduct certainly of Martian origin.*

#### **Figure 35.**

After many months of stop due to a serious pollution problem (see later), the SAM team started again its analytical work, on a soil sample of the site of Cumberland that was taken an year before, on May 2013 not far from John Klein. The SAM results were crucial [56]: aside from the usual light Chloro-derivatives, many chlorinated aromatics were detected [57] suggesting that they could be derived from organic molecules present in the mudstone (from bacteria or from a meteoric extract): between them also an abundant release (about 250 ppb) of Chlorobenzene was detected (**Figure 34**), so reaching for an other resemblance to the Viking results, in which Chloro-benzene (as mentioned before) was found after a

One of the most extraordinary SAM discovery was made at Pahrump Hills (at the base of3.5-billion-year-old Murray mudstone), located at the lowermost portion of the Sharp Mons (Gale Crater central mound), about 6–7 km southwest of Yellowknife Bay. This 3.5-billion-year-old Gale lake environment is expected to have been ideal settings for concentrating and preserving organic matter [58]. Two samples were drilled: Confidence Hills on sol 759 (24 Sep 2014), and Mojave on sol 882 (29 Jan 2015) (**Figure 35**). Confidence Hills soil was rich of hematite, Mojave soil was rich of jarosite, evidence of ancient passage of water. Because ultraviolet radiation and oxidizing compounds in the Martian soil would destroy any compounds exposed at the surface, Curiosity's scientists used a robotic drill to penetrate

To unlock organic molecules from the samples, the oven baked them to temper-

*December 2014: results by SAM-Curiosity from a powdered material drilled into the Cumberland sedimentary rock. Very important (bottom), between the GCMS evolved chloro-derivatives, the presence of chloro-benzene,*

atures of between 600°C and 860°C and fed the resulting fumes to the Mass Spectrometer, which identified a welter of closely related organic signals reflecting dozens or hundreds of types of small carbon molecules, such as aromatic rings and short aliphatic chains [59]. Abundant sulfur-bearing carbon rings called thiophenes,

were also detected and identified in the GC (**Figure 36**).

recent accurate re-examination of the original GCMS data [29].

several centimetres into the mudstone.

*Solar System Planets and Exoplanets*

**Figure 34.**

**158**

*a byproduct certainly of Martian origin.*

*Confidence Hills and Mojave drill sites, at Pahrump Hills location, were SAM made the main discovery of possible keragenic material.*

#### **Figure 36.**

*SAM-EGA evolved gases from Majave drilled material: sulfur-bearing carbon rings, short aliphatic chains and aromatic rings are typical decomposition products of keragenic material.*

The mass patterns looked like those generated on Earth by kerogen (aromatic rings, short aliphatic chains, sulphur containing molecules), a goopy high molecular material that is formed when geologic forces compress, during million of years, the ancient remains of algae and similar critters. Kerogen is sometimes found with sulfur, which helps preserve it across billions of years; the Curiosity scientists think the sulfur compounds in their samples also explain the longevity of the Mars compounds. At the moment, it is impossible to say whether ancient life explains the Martian organics. The signal, being found at the base of a lake 3,5 billion years old, when Mars environment was warm and wet, could be a potential catchment for the presence on Mars of archea bacteria in primordial epoch, possibly still present today where there are sources of liquid water over the surface (superficial melting of ices rich in salts) [60] or below the surface (sub-glacial lakes identified by radar tecniques) [61]. However, we must not forget that Carbon-rich meteorites and comets contain kerogenic like compounds, and constantly rain down on Mars …

It's disappointing that we can't figure out where the carbon-rich large molecules came from. But digging a little deeper could find better-preserved molecules in Mars rocks, to determine whether these molecules came from space, from igneous rocks, from hydrothermal activity, or – the most exciting possibility – ancient Mars life. Europe's ExoMars rover, due for launch in 2022, will drill deeper than Curiosity, to soil depths better protected from radiation. But probably, detection of past life may ultimately take the precision analysis of labs on Earth, bringing samples back. Fortunately, NASA Perseverance rover, that was successful in landing inside the Jezero crater on February 18, 2021 (**Figures 37** and **38**), is set to collect some 30 rock cores for return to Earth in subsequent missions.

SAM is able to give a further usefull help to determine the nature and origin of the kerogenic materials discovered on Mars, by the so called 'wet chemistry' experiments.

In summary, if organic molecules cannot enter the GCMS because a low volatility or breaking dawn under heating, they can be "derivatized" before they're heated – meaning that they react with some chemicals in order to become more volatile – so that they can be analyzed at a lower temperature. This derivatization process uses special chemical reagents dissolved in suitable solvents, so this experiment is called "wet chemistry". As yet mentioned, SAM only has nine Inconel steel cups containing these derivatizing agents: 7 containing a derivatization-silanizing

compound named MTBSTFA (N-tert-butyldimethylsilyl- N-

*The two derivatizing reagents for 'wet chemistry' on board of SAM-Curiosity.*

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

TMAH (tetramethylammonium hydroxide) (**Figure 39**).

*The MTBSTFA chemical mechanism of derivatization, called silanization.*

**Figure 39.**

**Figure 40.**

**161**

methyltrifluoroacetamide), 2 containing a thermochemolysis compound named

MTBSTFA is an organic compound containing Florine and Silicium, able to instantly replace active hydrogens on OH and NH2 (carboxylic acid, amine, aminoacid) with a N-tert-butyldimethylsilyl group (**Figure 40**): this non-polar moiety increases the volatility of the original compound by removing its polar nature, resulting in a much lower temperature needed for a GCMS analysis [62]. Due to the limited number of cups for 'wet chemistry', these kinds of experiments were obviously saved for only the most interesting rock samples. But an incredible accident caused the first wet chemistry trial to be postponed for six years. During the

#### **Figure 37.**

*The Jezero crater, an ancient lake where the rover Perseverance landed on February 18, 2021.*

#### **Figure 38.**

*February 21, 2021: Perseverance sees Jezero crater rim in 360° Mars panorama.*

#### **Figure 39.**

where there are sources of liquid water over the surface (superficial melting of ices rich in salts) [60] or below the surface (sub-glacial lakes identified by radar tecniques) [61]. However, we must not forget that Carbon-rich meteorites and comets contain kerogenic like compounds, and constantly rain down on Mars … It's disappointing that we can't figure out where the carbon-rich large molecules

came from. But digging a little deeper could find better-preserved molecules in Mars rocks, to determine whether these molecules came from space, from igneous rocks, from hydrothermal activity, or – the most exciting possibility – ancient Mars life. Europe's ExoMars rover, due for launch in 2022, will drill deeper than Curiosity, to soil depths better protected from radiation. But probably, detection of past life may ultimately take the precision analysis of labs on Earth, bringing samples back. Fortunately, NASA Perseverance rover, that was successful in landing inside the Jezero crater on February 18, 2021 (**Figures 37** and **38**), is set to collect some 30

SAM is able to give a further usefull help to determine the nature and origin of the kerogenic materials discovered on Mars, by the so called 'wet chemistry'

"wet chemistry". As yet mentioned, SAM only has nine Inconel steel cups containing these derivatizing agents: 7 containing a derivatization-silanizing

*The Jezero crater, an ancient lake where the rover Perseverance landed on February 18, 2021.*

*February 21, 2021: Perseverance sees Jezero crater rim in 360° Mars panorama.*

In summary, if organic molecules cannot enter the GCMS because a low volatility or breaking dawn under heating, they can be "derivatized" before they're heated – meaning that they react with some chemicals in order to become more volatile – so that they can be analyzed at a lower temperature. This derivatization process uses special chemical reagents dissolved in suitable solvents, so this experiment is called

rock cores for return to Earth in subsequent missions.

experiments.

*Solar System Planets and Exoplanets*

**Figure 37.**

**Figure 38.**

**160**

*The two derivatizing reagents for 'wet chemistry' on board of SAM-Curiosity.*

compound named MTBSTFA (N-tert-butyldimethylsilyl- Nmethyltrifluoroacetamide), 2 containing a thermochemolysis compound named TMAH (tetramethylammonium hydroxide) (**Figure 39**).

MTBSTFA is an organic compound containing Florine and Silicium, able to instantly replace active hydrogens on OH and NH2 (carboxylic acid, amine, aminoacid) with a N-tert-butyldimethylsilyl group (**Figure 40**): this non-polar moiety increases the volatility of the original compound by removing its polar nature, resulting in a much lower temperature needed for a GCMS analysis [62]. Due to the limited number of cups for 'wet chemistry', these kinds of experiments were obviously saved for only the most interesting rock samples. But an incredible accident caused the first wet chemistry trial to be postponed for six years. During the

examination of the results the SAM obtained on Rocknest and on John Klein, the SAM team discovered that a vial of MTBSTFA was broken, so polluting all the analytical system.

The problem was that MTBSTFA, being itself an organic compound, reacts under heat with perchlorates, giving the same kind of light chloro-derivatives (CH3Cl and CH2Cl2) found by the SAM on the Martian samples! From here a dreadful doubt that the origin of the 'positive' results obtained so far by the SAM could be 'terrestrial' and not Martian [25]. More than a year was needed to clean the system, during which a sample from Cumberland remained stored inside SAM, waiting the right moment to be analyzed. The sample remained 1280 sols (!) in contact with MTBSTFA vapors, a situation that also provided an opportunity [63]: baking the sample up to 900°C to verify if some reaction between MTBSTFA and Martian soil had happened. This so called 'opportunistic derivatization' was a success, because the GC–MS detected interesting compound such as Chlorobenzene, Thiophene, light Chloro-derivatives and many other unknown compounds (**Figure 41**).

Lab tests demonstrated that Chloro-benzene, an organic compound containing 6 Carbon atoms, could not be formed from the heating of MTBSTFA in presence of perchlorates [64] but only when various types of Martian organic materials are pyrolyzed (i.e. heated at high temperature) in presence of Chlorine source.

The first 'complete' wet chemistry experiment was made on December 19, 2017. The target was a Ogunquit Beach (OB) sand sample from the Bagnold dune field, chosen being easy to manipulate after months of trouble due recurrent problems with the drill feed mechanism (**Figure 42**).

About 45 mg of the Ogunquit Beach sand were added to one of the MTBSTFA cups and the mixture was heated up to 900°C. Reactions clearly occurred and produced derivatized compounds. GCMS results showed the detection of derivatized benzoic acid as well as excess, unreacted MTBSTFA. However, no amino acids or fatty acids were detected [65].

During the following months engineers found a way to fix the drill problem. So the next step was to perform wet chemistry experiments on drilled clay deeper samples, as these phyllosilicate-rich minerals are known to preserve organic matter exceptionally well. A unusual Mn- and P-rich clay-bearing unit named Glen Torridon (GT) (**Figure 43**) was discovered in the foothills of Mount Sharp by CRISM spectrometer aboard the Mars Reconnaissance Orbiter (strong absorptions at 2.24 and 2.29 μm. EGA analyses in many locations inside Glen Torridon showed emission of free and strongly linked water and, surprisingly, absence of emission of

O2 from perchlorates [66]: a promising situation in order to search for organic compounds. SAM activities in Glen Torridon included an EGA/GCMS analysis, a new MTBSTFA derivatization experiment, followed by the first TMAH experiment. On Sept. 24, 2019 (sol 2536) the rover placed in the SAM the powderized drilled

*The clay-bearing unit named Glen Torridon where SAM performed also the first derivatization with TMAH*

*Ogunquit Beach where SAM performed the first complete derivatization with MTBSTFA.*

aliphatic and aromatic compounds: dimethylsulfide, thiophene, and likely ethanethiol and dithiapentane. EGA also indicated results within the medium to high molecular weight ranges of masses, suggesting the presence of a complex

EGA/GCMS detected an abundance of S-bearing organic compounds, including

sample from GT- Glen Etive 2 site (**Figure 44**).

mixture of compounds.

**Figure 42.**

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

**Figure 43.**

**163**

*(called thermochemolysis).*

#### **Figure 41.**

*The GCMS result of the so called 'opportunistic derivatization', performed on Cumberland material, that stayed in touch for months with MTBSTFA vapors accidentally leaked from a broken cup.*

examination of the results the SAM obtained on Rocknest and on John Klein, the SAM team discovered that a vial of MTBSTFA was broken, so polluting all the

The problem was that MTBSTFA, being itself an organic compound, reacts under heat with perchlorates, giving the same kind of light chloro-derivatives (CH3Cl and CH2Cl2) found by the SAM on the Martian samples! From here a dreadful doubt that the origin of the 'positive' results obtained so far by the SAM could be 'terrestrial' and not Martian [25]. More than a year was needed to clean the system, during which a sample from Cumberland remained stored inside SAM, waiting the right moment to be analyzed. The sample remained 1280 sols (!) in contact with MTBSTFA vapors, a situation that also provided an opportunity [63]: baking the sample up to 900°C to verify if some reaction between MTBSTFA and Martian soil had happened. This so called 'opportunistic derivatization' was a success, because the GC–MS detected interesting compound such as Chlorobenzene, Thiophene, light Chloro-derivatives and many other unknown compounds

Lab tests demonstrated that Chloro-benzene, an organic compound containing 6 Carbon atoms, could not be formed from the heating of MTBSTFA in presence of perchlorates [64] but only when various types of Martian organic materials are pyrolyzed (i.e. heated at high temperature) in presence of Chlorine source.

The first 'complete' wet chemistry experiment was made on December 19, 2017. The target was a Ogunquit Beach (OB) sand sample from the Bagnold dune field, chosen being easy to manipulate after months of trouble due recurrent problems

About 45 mg of the Ogunquit Beach sand were added to one of the MTBSTFA cups and the mixture was heated up to 900°C. Reactions clearly occurred and produced derivatized compounds. GCMS results showed the detection of derivatized benzoic acid as well as excess, unreacted MTBSTFA. However, no

During the following months engineers found a way to fix the drill problem. So the next step was to perform wet chemistry experiments on drilled clay deeper samples, as these phyllosilicate-rich minerals are known to preserve organic matter exceptionally well. A unusual Mn- and P-rich clay-bearing unit named Glen Torridon (GT) (**Figure 43**) was discovered in the foothills of Mount Sharp by CRISM spectrometer aboard the Mars Reconnaissance Orbiter (strong absorptions at 2.24 and 2.29 μm. EGA analyses in many locations inside Glen Torridon showed emission of free and strongly linked water and, surprisingly, absence of emission of

*The GCMS result of the so called 'opportunistic derivatization', performed on Cumberland material, that*

*stayed in touch for months with MTBSTFA vapors accidentally leaked from a broken cup.*

analytical system.

*Solar System Planets and Exoplanets*

(**Figure 41**).

**Figure 41.**

**162**

with the drill feed mechanism (**Figure 42**).

amino acids or fatty acids were detected [65].

**Figure 42.** *Ogunquit Beach where SAM performed the first complete derivatization with MTBSTFA.*

#### **Figure 43.**

*The clay-bearing unit named Glen Torridon where SAM performed also the first derivatization with TMAH (called thermochemolysis).*

O2 from perchlorates [66]: a promising situation in order to search for organic compounds. SAM activities in Glen Torridon included an EGA/GCMS analysis, a new MTBSTFA derivatization experiment, followed by the first TMAH experiment. On Sept. 24, 2019 (sol 2536) the rover placed in the SAM the powderized drilled sample from GT- Glen Etive 2 site (**Figure 44**).

EGA/GCMS detected an abundance of S-bearing organic compounds, including aliphatic and aromatic compounds: dimethylsulfide, thiophene, and likely ethanethiol and dithiapentane. EGA also indicated results within the medium to high molecular weight ranges of masses, suggesting the presence of a complex mixture of compounds.

#### **Figure 44.**

*The Glen-Etive-2 site (Glen Torridon clay unit) where SAM-EGA discovered high molecular weight carbon molecules, possibly resulting from the breakdown of keragenic material.*

The possible discovery of high molecular molecules, was the long awaited reason for the first in situ TMAH wet chemistry experiment (**Figure 46**), the so called thermochemolysis, performed by hearing a sample of Martian soil in contact with one of the two cups onboard of SAM, containing tetramethylammonium hydroxide

This strongly alkaline reagent causes hydrolysis and methylation of -OH, -O-, -NH, and -SH groups bonds and, upon heating, thermal bond breakage (of big molecules) also enuses. Volatile products of thermochemolysis were directly analyzed by the mass spectrometer (EGA) or trapped and analyzed with gas chromatography mass spectrometry (EGA-GCMS). This amazing experiment was successfully executed in September 2020 at the Mary Anning (MA) drill site

'Bands' of masses grouped together and having mass-to-charge (m/z) 190 to 485, represent high molecular weight molecules detected by the SAM-MS. These

*The Mary Anning drill site (Glen Torridon clay unit) where the first TMAH derivatization was perfomed on*

(TMAH), dissolved in Methanol [68].

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

**Figure 46.**

**Figure 47.**

**165**

*September 2020.*

(**Figure 47**) in the Glen Torridon region [69, 70].

*The TMAH chemical mechanism of derivatization, called thermochemolysis.*

#### **Figure 45.**

*SAM EGA + CGMS have revealed a range of organic fragments detected above 500°C, indicating the presence of recalcitrant organic matter (e.g. macromolecles). Compounds in blue were only detected via GCMS. Compound in yellow are from Glen Torridon.*

The diversity of aromatics seems consistent with recalcitrant organic materials such as kerogenic-type macromolecules (remembering what was found at Cumberland and Mojeve five years before) (**Figure 45**).

MTBSTFA experiment showed the highest abundance of sulfur-bearing organics ever measured by the SAM instrument and a wide range of aromatic organic molecules including methylated polycyclic aromatic hydrocarbons (methylnaphthalene), a potential methylated ester carboxylic acid (benzoic acid) and Benzothiophene, all detected for the first time on Mars. However, no amino acids or fatty acids have been identified [67].

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

#### **Figure 46.**

*The TMAH chemical mechanism of derivatization, called thermochemolysis.*

The possible discovery of high molecular molecules, was the long awaited reason for the first in situ TMAH wet chemistry experiment (**Figure 46**), the so called thermochemolysis, performed by hearing a sample of Martian soil in contact with one of the two cups onboard of SAM, containing tetramethylammonium hydroxide (TMAH), dissolved in Methanol [68].

This strongly alkaline reagent causes hydrolysis and methylation of -OH, -O-, -NH, and -SH groups bonds and, upon heating, thermal bond breakage (of big molecules) also enuses. Volatile products of thermochemolysis were directly analyzed by the mass spectrometer (EGA) or trapped and analyzed with gas chromatography mass spectrometry (EGA-GCMS). This amazing experiment was successfully executed in September 2020 at the Mary Anning (MA) drill site (**Figure 47**) in the Glen Torridon region [69, 70].

'Bands' of masses grouped together and having mass-to-charge (m/z) 190 to 485, represent high molecular weight molecules detected by the SAM-MS. These

#### **Figure 47.** *The Mary Anning drill site (Glen Torridon clay unit) where the first TMAH derivatization was perfomed on September 2020.*

The diversity of aromatics seems consistent with recalcitrant organic materials such as kerogenic-type macromolecules (remembering what was found at Cumber-

*SAM EGA + CGMS have revealed a range of organic fragments detected above 500°C, indicating the presence of recalcitrant organic matter (e.g. macromolecles). Compounds in blue were only detected via GCMS.*

*The Glen-Etive-2 site (Glen Torridon clay unit) where SAM-EGA discovered high molecular weight carbon*

*molecules, possibly resulting from the breakdown of keragenic material.*

MTBSTFA experiment showed the highest abundance of sulfur-bearing organics

ever measured by the SAM instrument and a wide range of aromatic organic molecules including methylated polycyclic aromatic hydrocarbons (methylnaphthalene), a potential methylated ester carboxylic acid (benzoic acid) and Benzothiophene, all detected for the first time on Mars. However, no amino acids or

land and Mojeve five years before) (**Figure 45**).

fatty acids have been identified [67].

*Compound in yellow are from Glen Torridon.*

**Figure 44.**

*Solar System Planets and Exoplanets*

**Figure 45.**

**164**

#### **Figure 48.**

*The preliminary astonishing results of the TMAH thermochemolysis on the Martian soil drilled at Mary Anning. Separation was performed using a gas-chromatographic column (GC2) able to separated molecules with more than 15 Carbon atom. The red continuous line shows the ramp of temperature (adapted from A. Williams, fall 2020 AGU meeting).*

data may indicate that large, complex molecules were present. A variety of methylated, oxygen-, sulfur-, or nitrogen-bearing aromatic organics were detected in GCMS and/or EGA data. The presence of methylated single and double ring aromatics (included benzene, toluene, trimethyl- and tetramethyl-benzene, naphthalene, and methylnaphthalene) suggests that these organics might derive from a macromolecular source that was cleaved and methylated by TMAH thermochemolysis (**Figure 48**).

Examples of the organics detected in GCMS only include pentamethyl-benzene, benzoic acid methyl ester, dimethyl-, trimethyl-, and tetrame-thyl-benzenamine, dihydronaphthalene, 2-butyl-thio-phene, and benzothiophene. Pentamethylbenzene may be part of a multi-methylated benzene suite. The benzoic acid methyl ester reflects the reaction of TMAH methylating benzoic acid of indeterminate source. The multi-methylated benzenamine suite is also of indeterminate source. A non biological source of these organics on the surface of Mars could be the impact of meteoritic material. Several similar organics were indeed identified applying the TMAH thermochemolysis benchtop experiment to the Murchison meteorite, including toluene, trimethylbenzene, methylnaphthalene, 2-butylthiophene, and benzothiophene. Amines and amides are not prevalent in pyrolyzed Murchison material and benzenamines are also not generated during TMAH thermochemolysis of Murchison, so the origin of these amines remains at least problematic.

**Author details**

GAT/Milano Planetarium, Tradate, Italy

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

provided the original work is properly cited.

\*Address all correspondence to: c.guaita@libero.it

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

Cesare Guaita

**167**
