March 20th, 2016
The Arctic Ocean
Interestingly and coincidentally, “Arctic” comes from the Greek word αρκτος -arctos-, which means “bear” and is a reference to the constellation Ursa Minor, where is the North Star, which indicates the geographic North Pole .
The Arctic constitutes a unique ecosystem of the Earth, consisting of a large ice field, or ice-covered ocean, sometimes regarded as the northern part of the Atlantic Ocean, and it is surrounded by land, which is permafrost, with complete absence of trees. Life in the Arctic consists of organisms adapted to ice, including zooplankton and phytoplankton, fish, marine mammals, birds, land animals, plants and human societies fully adapted to the extreme conditions of the environment.
Due to global warming, isotherms are moving northward at a rate exceeding 50 km per decade over the past 30 years, so if we define the Arctic from a defined temperature or the tree line, its size is diminishing, being the reduction of sea ice the most visible effect.
Anthropogenic climate change: global warming, especially in the Arctic
Yes: climate change is here and it is generated by human activities, that is, it is anthropogenic. Previously there have been on Earth fluctuations in global temperature caused by natural phenomena, usually long-term and cyclical variations. For example, glaciations since about 2 million years are repeated every 100,000 years, and last ice age ended 15,000 years ago. So we are living now in an interglacial period and the next ice age could become not before 50,000 years. The cause of this cycle of glaciations seems to be orbital variations of the Earth, resulting in a lower insolation in high latitudes of the northern hemisphere during glacial periods.
Solar activity, like other stars, has cycles and roughly every 600 years there are periods of little activity (absence of very few solar spots and auroras), with lower energy output, which corresponds to cold periods in the Earth’s climate. The last minimal was in the period 1645-1715, and therefore from the middle of the eighteenth century we enjoy a maximum solar activity, with small cycles of minimum and maximum every 11 years.
Discounting these natural variations, it is clear that throughout the 20th century and especially since the 1960s there has been a steady increase in global average temperature (Figure 1), reaching almost 1ºC more than the beginning of the 20th century. In the early years of the current century the trend is worsening. The last 10 years have been the warmest since there are records, and the forecast is to continue increasing. Most experts agree that humans exert a direct impact on the heating process known as the greenhouse effect. The causes of this effect are some of gaseous components of the atmosphere, especially CO2, which has grown in parallel with rising temperatures, from about 300 ppm at the beginning of 20th century to nearly 400 ppm today. This CO2 and other gases as water vapour, methane and other exclusively anthropogenic absorb radiation and the result is that the atmosphere warms further.
Figure 1. Increase in average global temperature compared to the beginning of 20th century (from GISTEMP).
This global warming is particularly evident in the Arctic. The temperature increases are higher in northern latitudes, especially 60-70º N, where this past December 2015 (Figure 2) have raised to 9ºC above average in large areas of North America and Eurasia. This is called Polar Warming Amplification (PWA). The cause of this overheating in the Arctic respect of the rest of Earth is partly due to the loss of snow and ice (retroactive effect) because the largest area of land and water absorbs more solar energy than white ice (albedo effect), but also the PWA is partly due to the dynamic atmospheric transport, which transports heat energy from the clouds and subtropical regions to the north (Taylor et al 2013).
Figure 2. Thermal anomaly registered in December 2015 with respect to the average 1951-1980 (from GISTEMP).
Besides the consequences of this warming on the Arctic ice that we will comment below, another serious problem is the melting of permafrost, since then methane gas trapped under the frozen ground is released. This way, vast quantities of methane are released, and this greenhouse gas is contributing further to accelerate the global warming.
Less and less ice in the Arctic
Linear trends of sea ice extent and sea ice in the Arctic from 1979 to date are negative year after year, for any month is considered, but it is more clear by comparing Septembers, at the end of the summer when the ice is melting (Figure 3). Of the approximately 7 million km2 minimum in September (the maximum in March is about 16 million), about 100,000 km2 are melt per year, almost 9% every 10 years (Serreze et al 2007), so that there is now almost half ice than in 1979 (Figure 4).
Figure 3. Comparison of the extent of sea ice (in red): September 1979 and 2012 (from The Cryosphere Today).
Figure 4. Average monthly extension of Arctic sea ice since 1979 (Reeves et al 2013).
In addition to the reduction in surface ice, keep in mind the reduction in volume, representing now a third of what it was in September 1979.
There is a big difference between the different models for predicting the disappearance of Arctic sea ice. Half of them expect the total disappearance by September 2100. Predictions move since September 2040 the less optimistic until well past 2100 for the other (Serreze et al 2007).
Other problems resulting from the disappearance of sea ice are the ship traffic, which could shorten distances trips between the ports of northern countries, and on the other hand the exploitation of oilfields and other fossil fuels and minerals, since there is a large part of global reserves in the Arctic (Figure 5).
Figure 5. Left: forecast paths for open sea ships (blue) and for icebreakers (red) for 2040-2059. Right: Distribution of the potential major reserves of oil and gas (yellow) and licenses (red) and wells in operation or to operate (black). The dashed line indicates the limit of Conservation of Arctic Flora and Fauna (CAFF) declared by the Working Group of the Arctic Council (www.arctic-council.org). Figures from Reeves et al (2013).
Ecological consequences of the disappearance of the Arctic ice pack
There are many living beings linked to the ice. The polar bears roam on the Arctic ice, so we are feared for his fate. Many fish, seals and crustaceans (krill) form a food chain that starts from the algae that grow under the ice in a very consistent environment, rich in nutrients, especially favourable for marine life (Figure 6 A). Moreover, floating sea ice in summer is a good corridor for dispersion of terrestrial vertebrates (for instance arctic foxes) and plants.
The gradual disappearance of sea ice and warming in the Arctic coast involves a series of ecological imbalances (Figure 6 B). We see for example how walruses forced to remain grouped on the ground are more predisposed to disease transmission. The loss of sea ice diminishes dispersion by ice corridors and then the land populations are most isolated, thus gene flow is restricted. Polar bears and other predators that hunt on the sea ice have it much harder and their populations are at risk. Phytoplankton productivity decreases significantly, thereby reducing zooplankton, and then the whole food chain (fish, seals, etc.) is affected (Post et al 2013).
Figure 6. Ecological interactions influenced by sea ice. A: The distribution and seasonality of sea ice affects the abundance, distribution and interactions of the entire ecosystem in balance. B: The longest period without ice and less sea ice extent have disastrous consequences on the balance of the ecosystem (Post et al 2013).
The polar bear tries to survive
The polar bear (Ursus maritimus) is considered an endangered animal. There are only about 25,000 worldwide. The impact of climate change affects the exclusive habitat of polar regions and forecasts suggest that in a few years from now the ice of the Arctic will melt permanently and polar bears may become extinct because of warming area.
The polar bear is basically carnivorous, unlike others such as brown bears, and remains above the ice hunting seals. With the gradual disappearance of the ice it has more trouble finding preys, and some have begun to learn how to catch salmon rivers, as we see in the images (Figure 7).
Figure 7. White Bear dedicated to fishing salmons in order to survive (www.youtube.com/watch?v=9m_Q9Ojbcmw).
We have also seen groups of polar bears at sea fishing (see video) and dive emerging alternately as if they were dolphins or porpoises. Despite these small adaptations, the food is very low and it is clear that their populations are declining rapidly.
Orcas thrive north
The disappearance of the northern ice is a dramatic ecological change that is causing the disappearance of some species like the polar bear, but interestingly these imbalances benefit some other emerging species. This is the case of the killer whale (Orcinus orca), which is thriving more and more to the north (Figure 8).
Figure 8. Places (marked with numbers) of the Canadian Arctic where groups of orcas were repeatedly photographed between 2004 and 2009 (Young et al 2011).
Eskimo Inuit people live around the American Arctic (from Quebec to Alaska including Hudson Bay and adjacent islands) and the west coast of Greenland, and they are the first witnesses since the mid-twentieth century observing whales in their waters, unknown before. Moreover, in recent years scientists have made numerous orca’ sightings, they have been photographed individually (Young et al 2011), and their travels have been followed through bioacoustics (Ferguson et al 2010) and other techniques.
Figure 9. (Top): Narwhals with the characteristic great tusk, which gave rise to the myth of the unicorn. (Low): Group of orcas attacking narwhals cornered on the beach. Watch the video of PBS Nature.
For some years attacks by orcas on narwhals (as in Figure 9) have been observed repeatedly by Inuit Eskimos and studied in detail by several scientists. Laidre et al (2006) observed that before approaching whales, the narwhals tend to group, are more quiet and swim closer to the beach in shallow waters. During the attack, the narwhals disperse significantly but nevertheless mortality is very high. After predation, which can last several hours, oily stains are observed in sea surface, which come from fat of depredated narwhals (Figure 10).
Figure 10. Group of orcas surrounded by patches of oil on the sea surface from the fat of attacked narwhals (Laidre et al 2006).
Orcas’ attacks on narwhals are so common and effective that are beginning to affect the population. The effects are even worse in other cetaceans with smaller population such as whales of Greenland or bowhead (Balena mysticetus), which are now virtually extinct (Figure 11).
Figure 11. Scheme of preys’ proportions by a group of orcas from Hudson Bay (Ferguson et al 2010).
In conclusion, anthropogenic climate change is affecting the Arctic ecosystem severely (and all the other ecosystems), and although this problem is becoming known, effective policy measures to reduce emissions of CO2 and other greenhouse gases are so scarce that hardly will arrive in time. We are leading the planet Earth to a massive extinction of species and ecological changes ever seen in the history of humans.
The picture says it all: polar bear habitat is running out.
Arctic Council: http://www.arctic-council.org
Ferguson S.H., Higdon J.W. & Chmelnitsky E.G. (2010) The rise of killer whales as a major Arctic predator. In S.H. Ferguson, et al. (eds.): A little less Arctic: top predators in the world’s largest northern inland sea, Hudson Bay. Pp. 117–136. New York: Springer
GISTEMP, Goddard Institute for Space Studies Surface Temperature Analysis (NASA-GISS): http://data.giss.nasa.gov/gistemp/
Hawkings E (2014) nov 28: http://www.climate-lab-book.ac.uk/2014/hiatuses-in-the-rise-of-temperature/
Laidre KL, Heide-Jørgensen MP, Orr J (2006) Reactions of narwhals, Monodon monoceros, to killer whale, Orcinus orca, attacks in the Eastern Canadian Arctic. Can. Field Nat., 120, 457–465
Morell V (2012) Killer whale menu finally revealed. http://www.sciencemag.org/news/2012/01/killer-whale-menu-finally-revealed
Post et al. (2013) Ecological Consequences of Sea-Ice Decline. Science. DOI: 10.1126/science.1235225: http://www.carbonbrief.org/knock-on-effects-for-wildlife-as-the-arctic-loses-ice
Reeves RR et al (2014) Distribution of endemic cetaceans in relation to hydrocarbon development and commercial shipping in a warming arctic. Marine Policy 44, 375-389
Serreze MC, Holland MM, Stroeve J (2007) Perspectives on the Arctic’s shrinking sea-ice cover. Science 315, 5818, 1533–6.
Taylor PC, Cai M, Hu A, Meehl J, Washington W, Zhang GJ (2013) Decomposition of feedback contributions to Polar Warming Amplification. J Climate 26, 7023-43
The Cryosphere Today: http://arctic.atmos.uiuc.edu/cryosphere/
Young BG, Jeff W. Higdon JW, Steven H. Ferguson SH (2011) Killer whale (Orcinus orca) photo-identification in the eastern Canadian Arctic. Polar Research Vol 30
21st March 2015
Clostridia: who are they ?
The clostridia or Clostridiales, with Clostridium and other related genera, are Gram-positive sporulating bacteria. They are obligate anaerobes, and belong to the taxonomic phylum Firmicutes. This phylum includes clostridia, the aerobic sporulating Bacillales (Bacillus, Listeria, Staphylococcus and others) and also the anaerobic aero-tolerant Lactobacillales (id est, lactic acid bacteria: Lactobacillus, Leuconostoc, Oenococcus, Pediococcus, Lactococcus, Streptococcus, etc.). All Firmicutes have regular shapes of rod or coccus, and they are the evolutionary branch of gram-positive bacteria with low G + C content in their DNA. The other branch of evolutionary bacteria are gram-positive Actinobacteria, of high G + C and irregular shapes, which include Streptomyces, Corynebacterium, Propionibacterium, and Bifidobacterium, among others.
Being anaerobes, the clostridia have a fermentative metabolism of both carbohydrates and amino acids, being primarily responsible for the anaerobic decomposition of proteins, known as putrefaction. They can live in many different habitats, but especially in soil and on decaying plant and animal material. As we will see below, they are also part of the human intestinal microbiota and of other vertebrates.
The best known clostridia are the bad ones (Figure 1): a) C. botulinum, which produces botulin, the botulism toxin, although nowadays has medical and cosmetic applications (Botox); b) C. perfringens, the agent of gangrene; c) C. tetani, which causes tetanus; and d) C. difficile, which is the cause of hospital diarrhea and some postantibiotics colitis.
Figure 1. The four more pathogen species of Clostridium. Image from http://www.tabletsmanual.com/wiki/read/botulism
Clostridia in gut microbiota
As I mentioned in a previous post (Bacteria in the gut …..) of this blog, we have a complex ecosystem in our gastrointestinal tract, and diverse depending on each person and age, with a total of 1014 microorganisms. Most of these are bacteria, besides some archaea methanogens (0.1%) and some eukaryotic (yeasts and filamentous fungi). When classical microbiological methods were carried out from samples of colon, isolates from some 400 microbial species were obtained, belonging especially to proteobacteria (including Enterobacteriaceae, such as E. coli), Firmicutes as Lactobacillus and some Clostridium, some Actinobacteria as Bifidobacterium, and also some Bacteroides. Among all these isolates, some have been recognized with positive effect on health and are used as probiotics, such as Lactobacillus and Bifidobacterium, which are considered GRAS (Generally Recognized As Safe).
But 10 years ago culture-independent molecular tools began to be used, by sequencing of ribosomal RNA genes, and they have revealed many more gut microorganisms, around 1000 species. As shown in Figure 2, taken from the good review of Rajilic-Stojanovic et al (2007), there are clearly two groups that have many more representatives than thought before: Bacteroides and Clostridiales.
Figure 2. Phylogenetic tree based on 16S rRNA gene sequences of various phylotypes found in the human gastrointestinal tract. The proportion of cultured or uncultured phylotypes for each group is represented by the colour from white (cultured) passing through grey to black (uncultured). For each phylogenetic group the number of different phylotypes is indicated (Rajilic-Stojanovic et al 2007)
In more recent studies related to diet such as Walker et al (2011) — a work done with faecal samples from volunteers –, population numbers of the various groups were estimated by quantitative PCR of 16S rRNA gene. The largest groups, with 30% each, were Bacteroides and clostridia. Among Clostridiales were included: Faecalibacterium prausnitzii (11%), Eubacterium rectale (7%) and Ruminococcus (6%). As we see the clostridial group includes many different genera besides the known Clostridium.
In fact, if we consider the population of each species present in the human gastrointestinal tract, the most abundant seems to be a clostridial: F. prausnitzii (Duncan et al 2013).
Benefits of some clostridia
These last years it has been discovered that clostridial genera of Faecalibacterium, Eubacterium, Roseburia and Anaerostipes (Duncan et al 2013) are those which contribute most to the production of short chain fatty acids (SCFA) in the colon. Clostridia ferment dietary carbohydrate that escape digestion producing SCFA, mainly acetate, propionate and butyrate, which are found in the stool (50-100 mM) and are absorbed in the intestine. Acetate is metabolized primarily by the peripheral tissues, propionate is gluconeogenic, and butyrate is the main energy source for the colonic epithelium. The SCFA become in total 10% of the energy obtained by the human host. Some of these clostridia as Eubacterium and Anaerostipes also use as a substrate the lactate produced by other bacteria such as Bifidobacterium and lactic acid bacteria, producing finally also the SCFA (Tiihonen et al 2010).
Clostridia of microbiota protect us against food allergen sensitization
This is the last found positive aspect of clostridia microbiota, that Stefka et al (2014) have shown in a recent excellent work. In administering allergens (“Ara h”) of peanut (Arachis hypogaea) to mice that had been treated with antibiotics or to mice without microbiota (Germ-free, sterile environment bred), these authors observed that there was a systemic allergic hyper reactivity with induction of specific immunoglobulins, id est., a sensitization.
In mice treated with antibiotics they observed a significant reduction in the number of bacterial microbiota (analysing the 16S rRNA gene) in the ileum and faeces, and also biodiversity was altered, so that the predominant Bacteroides and clostridia in normal conditions almost disappeared and instead lactobacilli were increased.
To view the role of these predominant groups in the microbiota, Stefka et al. colonized with Bacteroides and clostridia the gut of mice previously absent of microbiota. These animals are known as gnotobiotic, meaning animals where it is known exactly which types of microorganisms contain.
In this way, Stefka et al. have shown that selective colonization of gnotobiotic mice with clostridia confers protection against peanut allergens, which does not happen with Bacteroides. For colonization with clostridia, the authors used a spore suspension extracted from faecal samples of healthy mice and confirmed that the gene sequences of the extract corresponded to clostridial species.
So in effect, the mice colonized with clostridia had lower levels of allergen in the blood serum (Figure 3), had a lower content of immunoglobulins, there was no caecum inflammation, and body temperature was maintained. The mice treated with antibiotics which had presented the hyper allergic reaction when administered with antigens, also had a lower reaction when they were colonized with clostridia.
Figure 3. Levels of “Ara h” peanut allergen in serum after ingestion of peanuts in mice without microbiota (Germ-free), colonized with Bacteroides (B. uniformis) and colonized with clostridia. From Stefka et al (2014).
In addition, in this work, Stefka et al. have conducted a transcriptomic analysis with microarrays of the intestinal epithelium cells of mice and they have found that the genes producing the cytokine IL-22 are induced in animals colonized with clostridia, and that this cytokine reduces the allergen uptake by the epithelium and thus prevents its entry into the systemic circulation, contributing to the protection against hypersensitivity. All these mechanisms, reviewed by Cao et al (2014), can be seen in the diagram of Figure 4.
In conclusion, this study opens new perspectives to prevent food allergies by modulating the composition of the intestinal microbiota. So, adding these anti-inflammatory qualities to the production of butyrate and other SCFA, and the lactate consumption, we must start thinking about the use of clostridia for candidates as probiotics, in addition to the known Lactobacillus and Bifidobacterium.
Figure 4. Induction of clostridia on cytokine production by epithelial cells of the intestine, as well as the production of short chain fatty acids (SCFA) by clostridia (Cao et al 2014).
Cao S, Feehley TJ, Nagler CR (2014) The role of commensal bacteria in the regulation of sensitization to food allergens. FEBS Lett 588, 4258-4266
Duncan SH, Flint HJ (2013) Probiotics and prebiotics and health in ageing populations. Maturitas 75, 44-50
Rajilic-Stojanovic M, Smidt H, de Vos WM (2007) Diversity of the human gastrointestinal tract microbiota revisited. Environ Microbiol 9, 2125-2136
Rosen M (2014) Gut bacteria may prevent food allergies. Science News 186, 7, 4 oct 2014
Russell SL, et al. (2012) Early life antibiotic-driven changes in microbiota enhance susceptibility to allergic asthma. EMBO Rep 13(5):440–447
Stefka AT et al (2014) Commensal bacteria protect against food allergen sensitization. Proc Nat Acad Sci 111, 13145-13150
Tiihonen K, Ouwehand AC, Rautonen N (2010) Human intestinal microbiota and healthy aging. Ageing Research Reviews 9:107–16
Walker AW et al (2011) Dominant and diet-responsive groups of bacteria within the human colonic microbiota. The ISME J 5, 220-230
As I mentioned in this blog a year and a half before (August 30th, 2012 “Is there life on Mars?”), the Curiosity rover began to walk by Mars, specifically inside the Gale crater, carrying its sophisticated instruments to analyze rocks, soil and atmosphere, that is, a well equipped geochemical laboratory analyzing the surface of another planet for the first time. You can see a video of 2 minutes of the 1st year of Curiosity here. As you know, one of the objectives of this analysis is to find evidence of whether there were favorable conditions for life on Mars, albeit in very bygone eras.
The Curiosity rover is walking inside Gale Crater, east of Syrtis Major, the Mars most prominence visible through a telescope. Image NASA/ESA/Hubble.
Mars is a planet with some similar features on Earth, such as the length of day, slightly more than 24 hours, but the greater distance from the Sun and very tenuous atmosphere make the average temperature to be -63 ° C, with daily oscillations from +20°C to -140°C. Having no oceans, the land surface of Mars is equivalent to the Earth, because Mars is smaller.
Comparison of Earth and Mars. The diameter of Mars is 3400 km, approx half of the Earth’s, but excluding oceans, the solid surface is similar on both planets. Image taken from T.E. Harrison, New Mexico State University.
Despite the difficulties to demonstrate the current existence of liquid water on Mars, from some years ago evidences have been found that there was water in the Martian surface, and it is being confirmed that during the first thousand million years there was plenty of water on Mars (Remind that both Mars and Earth are about 4.5 billion years).
Appearance of a region of Mars indicating the flow of water in the distant past. Image taken from T.E. Harrison, New Mexico State University.
Water history in Mars, in billions of years. Image from T.E. Harrison, New Mexico State University.
Curiosity shows an “habitable” lake 3800 million years ago
Thus, Curiosity rover has been taking samples in various ways (see in Figure below the 5 cm holes taking samples) and analyzing them. Studying the data, scientists have been able to write a series of articles that have been published in Science and other prestigious journals.
Two 5 cm holes made by Curiosity rover sampling in Yellowknife Bay of Gale Crater on Mars (NASA/JPL-Caltech/MSSS)
Among other articles, by last May was already published one (Williams et al 2013) with observations that the material extracted from the Yellowknife Bay of Gale Crater shows textures typical of fluvial sedimentary conglomerates, with rounded pebbles that indicate fluvial abrasion, and by their characteristics a water flow of nearly 1 meter per second has been deduced, with a depth of near 1 meter. Therefore, when this area was formed the climatic conditions, with abundant rivers, would have been very different from the current hyperarid and very cold environment.
A few weeks ago, on December 9th, Science Online has released a special edition dedicated to the latest findings of Curiosity, with 6 articles asserting that at Gale Crater there would have been a lake theoretically habitable for some organisms.
In one of the articles, maybe the most relevant one, Grotzinger et al (2013) describe the sedimentary rocks found by the rover and demonstrate that it corresponded to an aqueous environment with neutral pH, low salinity and different redox states of Fe and S. The presence of C, H, O, S, N and P (i.e., all biogenic elements) is also shown, and the authors estimate that this favorable environment for life could have lasted some few hundred thousand years, and therefore it demonstrates the biological feasibility of this fluvio-lacustrine environment of post-Noachian Mars, that is, about 3800 million years ago.
Therefore, these scientists deduced that this lake had fresh water, a water we could drink, and that around this lake various fluvial and lacustrine environments were present. This environment should be habitable for some organisms, and very similar to some current earth environments. The commented chemical compounds would be suitable for the survival of bacteria chemolithotrophic bacteria, id est, those which use inorganic compounds (such as Fe or S) as an energy source and use CO2 as a carbon source. On Earth we have many kind of these microbes, such as iron bacteria (Thiobacillus) or sulfur bacteria (including some sulfur thermophilic archaea) and the nitrifying ones. Although most of these chemolithotrophic bacteria on Earth are aerobic because they use atmospheric oxygen as electron acceptor, this metabolism is also known in some anaerobes, such as those that do the anoxic ammonium oxidation (process “Anammox”), for example Brocadia anammoxidans, or the same nitrifying bacteria in anaerobic conditions.
Therefore, with this habitable lake for some time, and with other similar environments, we can not reject the possibility that living beings had been sometimes in Mars.
View from Yellowknife Bay in Gale Crater, looking W-NW. This area of sedimentary deposits was the bottom of a freshwater lake. Photo: NASA/JPL-Caltech.
Estimated size and shape of the lake that was in the Gale crater. There must have been other similar. The arrows indicate the direction of the alluvial fan that flowed into the crater from its wall. Photo: NASA/JPL-Caltech/MSSS.
Another aspect studied in this extra issue of Science is the possible presence of methane in the Martian atmosphere (Webster et al 2013). Just like on Earth, methane is a potential sign of biological activity in the past. Previous observations made from Earth or from the Mars orbit speculated on the presence of some 10 ppb of methane, and its subsurface biological origin was also discussed. Nevertheless, in the measurements made in situ by laser spectrometry of Curiosity rover using a specific spectral methane pattern, it has not been detected since the values found are lower than 1 ppb. This reduces the probability of recent methanogenic microbial activity on Mars and it is limiting the possible contribution of recent geological and extraplanetary sources.
Finally, in another article (Hassler et al 2013) about measures of cosmic rays on the surface of Mars that Curiosity has made over a year, models of radiation are elaborated, for the time calculation of possible subsurface microbial survival, and also for the preservation of organic compounds of biological origin finding them billions of years later. Unfortunately, the conclusion is that the powerful effect of cosmic rays would cause very difficult any of these possibilities. Unlike the Earth, the magnetic field of Mars is very weak and the atmosphere too, things that help bombardment of cosmic rays and the solar wind on the Martian surface. However, there is evidence that in the past Mars had a magnetic field more effective, so hope is not lost …..
Achenbach J. 2013. NASA Curiosity rover discovers evidence of freshwater Mars lake. The Washington Post, Health & Science online Dec 9.
Anderson PS. 2013. Curiosity rover confirms ancient martian lake. Spaceflight Insider online Dec 11.
Grotzinger JP et 72 al. 2013. A Habitable Fluvio-Lacustrine Environment at Yellowknife Bay, Gale Crater, Mars. Science DOI: 10.1126/science.1242777 online Dec 9, 2013.
Harrison, T.E., New Mexico State University: http://astronomy.nmsu.edu/tharriso/ast105/Mars.html
Hassler DM et 23 al. 2013. Mars’ Surface Radiation Environment Measured with the Mars Science Laboratory’s Curiosity Rover. Science DOI: 10.1126/science.1244797 online Dec 9, 2013.
Kerr, RA. 2013. New Results Send Mars Rover on a Quest for Ancient Life. Science Now News, online Dec 9, 2013.
Science Special Collection Curiosity 2013. Curiosity at Yellowknife Bay, Gale Crater. Online: http://www.sciencemag.org/site/extra/curiosity/
Webster CR et al 2013. Low upper limit to methane abundance on Mars. Science 18 October 2013, Vol. 342 no. 6156 pp. 355-357
Williams RME et 38 al. 2013. Martian Fluvial Conglomerates at Gale Crater. Science 31 May 2013, Vol. 340 no. 6136 pp. 1068-1072
Just three weeks ago I wrote here (Few news from Mars …….) a post on a study that provided disappointing evidence that Martian clay would not have been made with liquid water. With that, existence of water on Mars should be less likely, and therefore life in this planet.
However, this past week the NASA’s Curiosity rover sent us a picture of the Martian surface rocks with an aspect which seem to be the product of a stream in the past.
According to NASA scientists, the shapes of these stones and their arrangement as gravel, are evidence of the remains of an old water streambed flowing down the slopes of Gale Crater, where the spacecraft mission to Mars Science Laboratory Curiosity landed in early August. This place has been called Hottah by NASA, by reminiscence of a rock formation in Canada with that name.
Details of the photo (see below) show that these rocks are a conglomerate of stones, some of which are rounded and therefore likely product of water transport. From the size of gravels it carried, NASA scientists even have calculated that the water was moving about one meter per second, so it was a very impetuous flow.
So this would be another evidence that in the past Mars had liquid water, and therefore the chances of life there have been increased. In fact, this is not the first finding that points to the possibility that there was water on Mars, since the first mission Mariner 9 in 1971 had already seen geological formations that seemed river beds and canyons .
In addition to the clays that I mentioned in my previous post, another possible evidence of water was found a year ago, when the Opportunity rover (much more “primitive” than the Curiosity), which is in Mars for 8 years, found bright veins of a mineral (picture here below), apparently gypsum, in Endeavour crater. As gypsum is formed by sedimentation with water on Earth, it is likely that this was the origin of that material on Mars some thousand million years ago.
The NASA scientists say these photos taken now by Curiosity are a great evidence of liquid water. Anyway, I do not want to be faithless, but I do not know if these stones and their arrangement could have been made otherwise, who knows, other liquid materials, or wind erosion, I do not know.
Well, as the same scientists from NASA say, this Curiosity mission planned for two years is beyond the visual confirmation of an old streambed. Analyses that the Curiosity equipment will do should allow to understand the chemical composition of these materials and their origin, trying to learn when and why Mars was dry, if the planet had been wet before. For this reason, Curiosity has to explore Mount Sharp, which is about 6 km from the center of the crater where it landed. At the base of this mountain there are clays and sulfates, according orbital observations, and therefore Curiosity will climb this mountain, 700 meters high, and there will help scientists decipher the history of Mars, wet and dry, and find some other evidences of the possibility of past life on Mars, and its habitability today.
NASA, News Releases, NASA Rover Finds Old Streambed On Martian Surface, 27 sept 2012
Mike Wall, Space.com Senior Writer, Curiosity’s ancient streambed discovery is just the latest clue. Space on NBCNews.com
IAS Preparation Online, Curiosity finds ancient stream bed on Mars
Mike Wall, Space.com Senior Writer, NASA Rover finds convincing evidence of water on Mars. Space.com
Two weeks ago I wrote in this blog (Is there life on Mars?) on the Mars Science Laboratory mission of NASA with the famous Curiosity rover, which its main aim is finding possible signs of past life in the red planet.
Well, as expected, until now there are no spectacular news, as in all scientific studies, things take time. The Curiosity has been taking photos (see one here) and taking samples and analyzing them. Today there are 40 days since the landing and it has walked about 150 meters. As stated in the last NASA chronicle, Curiosity continues its work “in good health”. So keep waiting.
But today I want to comment some disappointing news regarding the possibilities that there had been life on Mars. It turns out that a recent study of French and American researchers (Meunier et al, 2012) provides evidences that Martian clays could have a direct magmatic origin and therefore they would not have made by contact of the basaltic crust with liquid water, as hypothesized until now. And so, the less likely the existence of liquid water on Mars in the past, less likelihood of living beings there.
Clays are hydrous silicates (of phyllosilicates group), mainly of aluminium (Al2O3 · 2 SiO2 · 2 H2O). They are minerals with granular structure, which originate on Earth mainly by decomposition of magmatic rocks containing silicate minerals such as the feldspar by the action of liquid water (this may contain carbonic acid and other compounds). Clays have been identified on Mars some years ago with the spectrometers of the OMEGA observatory carried by the Mars Express spacecraft of the European Agency, which is orbiting Mars (Bibring et al, 2006). It was believed until now that these clay minerals, abundant in Mars surface, would have been formed for a long time by interaction of liquid water with basaltic crust, decomposing the magmatic rocks, but early in Mars history, 3700 million years ago, at the same time that Earth life was beginning. The presence of liquid water would be a sign of warmer and wetter conditions on early Mars, and therefore more likely to carry life.
But the recent published work of Meunier et al. suggests a different mechanism that does not require prolonged reaction of rocks with water. Interestingly, evidence has been found on Earth, studying clays of Mururoa Atoll in French Polynesia, which are similar to Martians phyllosilicate clays. Using petrographic techniques (study of the mineral structures at the microscopic level), microanalysis of elements, and isotope ratio analysis, these researchers have found that the Mururoa clays, rich in Fe and Mg, are much richer in rare earth elements (lanthanides and other), and microscopic structures are very different from other more abundant clay on Earth, originated from aqueous weathering. The characteristics of the Mururoa clays assert that were originated by short pulses of degassing magma in the interstices of basalt, and the water contained in clays would be only of magmatic origin.
Meunier et al. have also studied clays of Martian meteorites and have found that some of them have similar characteristics as those of Mururoa. Especially the ratio of the isotopes carbon-13 and deuterium in Lafayette meteorite shows that their clay was formed by direct precipitation of magmatic fluid containing water, by degassing magma.
Therefore, if martian clays, very similar to those of Mururoa (at least in their spectra), are proved to be formed also by magmatic degassing, then the presence of liquid water in early Mars would be more difficult to prove, and this planet would not have had easy conditions of habitability, at the same early period when life began to flourish on Earth.
The place where Curiosity is walking around, the Gale Crater, is known to contain phyllosilicates, i.e. clays. So, we must therefore wait that this rover could find clays and analyze them, and wait for some news a little more optimistic.
Bibring, J-P. et al (2006) Global mineralogical and aqueous Mars histoy derived from OMEGA/Mars Express Data. Science 312, 5772, 400-404
Hynek, B. (2012) Planetary science: Unhabitable martian clays ? Nature Geoscience, News and Views, online 9 sept 2012: http://dx.doi.org/10.1038/ngeo1560
Meunier, A. et al (2012) Magmatic precipitation as a possible origin of Noachian clays on Mars. Nature Geoscience, online 9 sept 2012: http://dx.doi.org/10.1038/ngeo1572
As you know, these days Mars is back in fashion. On August 6th, we have seen the Mars Science Laboratory (MSL) of the NASA  landing successfully on the red planet, and now the Curiosity rover is walking to see what is there. This robot of about 900 kg, the largest that has been managed to land safely on Mars, is very well equipped. It contains 10 scientific instruments, including infrared laser teledetector, mass spectrometer, gas chromatograph, X-ray diffraction, microscopic camera, radiation detector, weather stations, and more than 17 photographic cameras .
These equipments are designed to detect any trace of water, to analyze accurately the rocks, to study the minerals in the Martian surface, to measure the chirality of the molecules detected (you know, L-or D-, such as L-amino acids typical of living beings) and to take pictures in high resolution.
The Curiosity rover, of Mars Science Laboratory mission, NASA
With these tools, the main objective of the MSL is determining whether there have been conditions conducive to life in Mars. Therefore, rather than looking directly for finding living beings, the goal is to try to find if there are any signs of past or present life, and also for looking the possibilities for a possible human settlement.
Life as we know it on Earth is based on the chemical elements of the basic biochemistry, namely carbon, oxygen, hydrogen, nitrogen, phosphorous, sulphur, and other trace elements. While these elements are found in many parts of the outer space, including Mars, it is necessary to quantify them to see if their proportions are indicative of a possible life, present or past, on Mars.
Of course, a key point in the search for life is to find liquid water, since on Earth there are living beings wherever there is liquid water, regardless of other conditions, aerobic or not, and extreme pHs and other inhospitable conditions. As you know, there are organisms on Earth everywhere, and among the so called extremophiles, either archaea or bacteria, there are some living at sea depths with enormous pressures, some others living at pH below 1 and temperatures near the boiling point, others a few hundred meters underground, others in the upper atmosphere, others endure radiation, others in a high osmotic pressure (e.g. saline environments). But in all cases, and even sometimes with very few nutrients, organisms live always in the presence of liquid water, even at low concentration. On Earth, wherever there is liquid water, always living beings are found, mainly microorganisms.
So well, is there liquid water in Mars ? It seems highly unlikely, but not impossible at all. There is water, certainly, especially ice at the poles (see picture) and in other places, but the low atmospheric pressure (the highest on the Martian surface is 0.6% of the Earth’s one), makes ice sublimating directly to water vapour, which is hardly retained by the atmosphere and escapes the planet. The Martian atmosphere contains 95% CO2, 3% N2, and traces of oxygen and water, as well as many particles in suspension. These give a tawny colour to the atmosphere, similar to the aspect of the planet as we see, due to abundance of iron oxide. Surface temperatures oscillate from about -140 °C at the poles to about 35 °C, occasionally at the equator. Therefore, even temporarily, there can be liquid water.
True-colour view of Mars seen through NASA’s Hubble Space Telescope
Despite the current hostile conditions of Mars, there is geological evidence of the existence of liquid water in the past, like the geomorphology of valleys and channels, etc., and also by the presence of some minerals that only can be originated with water (e.g. hematite).
On the other hand, small amounts of methane and formaldehyde have been detected there. These compounds are mostly generated biologically on Earth, but conditions of the Martian atmosphere make them short-lived . However, their geological origin seems also possible.
The habitability of Mars has been tested in the laboratory reproducing its conditions, by placing polar and alpine lichens at these conditions . Surprisingly, it has been shown that these lichens can resist them.
The question of possible life on Mars had a peak in 1996, when scientific staff from NASA published in Science magazine  the microscopic images of a fragment of ALH84001, a meteorite from Mars. This stone seems to be of Martian origin, it was launched into space by the impact of a meteorite on Mars about 15 million years ago, and then it travelled till the Earth reaching the Antarctica, where it was found in 1984. The structures seen there recall bacterial chains, and so, it was proposed that they would be martian microfossils. However, there is no other evidence of the biological origin of these structures and afterwards an inorganic origin of the meteorite minerals has been proposed .
Electronic microscopy of a fragment of ALH84001 meteorit (image of NASA)
Well, we wait with expectation the results of the tests done by the Curiosity. If evidence of past or present life on Mars is found, there will be very much to think about, especially in the sense that terrestrial organisms would not be alone in the universe. And in spite of the evidence that would be very simple microbial life, we should conclude that life is a feature very widespread in the universe.
What do you think ? Will Curiosity find evidence of life on Mars ?
Earth and Mars, at the same scale, two Bio-planets ? (image from NASA)
 NASA: http://www.nasa.gov/mission_pages/msl/
 Mahaffy, P. (2009) Sample analysis at Mars: Developing analytical tools to search for a habitable environment on the red planet. Geochemical News (Geochemical Society), 141, oct. 2009
 Krasnopolski, V.A. et al. (2004). Detection of methane in the Martian atmosphere: evidence for life?”. Icarus 172, 537–547
 DLR (German Aerospace Center) Surviving the conditions on Mars: http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10081/151_read-3409/
 McKay, D.S. et al. (1996) Search for past life on Mars: Possible relic biogenic activity in Martian meteorite ALH84001. Science 273, 924–930
 Golden, D.C. et al. (2004) Evidence for exclusively inorganic formation of magnetite in Martian meteorite ALH84001. American Mineralogist 89, 681–695
[ ] … and Wikipedia:
– Mars Science Laboratory: http://en.wikipedia.org/wiki/Mars_Science_Laboratory