CR
Cryospheric Sciences

Mars

Image of the Week – Ice caps on Mars?!

Image of the Week – Ice caps on Mars?!

Much like our Planet Earth, Mars has polar ice caps too, one for each pole: the Martian North Polar Ice Cap (shown on our image of the week) and the Southern Polar Ice Cap. Yet, their composition and structure reveals these ice caps are quite different from those of Planet Earth…


Mars refresher

 

Planet Earth and planet Mars [Credit : NASA]

As a refresher, here are some Mars facts:

  • Mars is the 4th planet from the sun.
  • Its equatorial diameter is half the size of the Earth’s, but is bigger than our moon’s.
  • Its mean surface temperature is -63°C (the Earth’s surface is around 14°C)
  • Mars’ atmosphere is 96% carbon dioxide, less than 2% argon, less than 2% nitrogen and less than 1% other gases.
  • Mars’ rotational axis has a tilt similar to Earth’s giving it four seasons as well .

For more detailed pictures and facts about Mars, go have a look on the NASA website here.

What are these Martian ice caps like?

Like Earth, both of Mars’ poles are frozen. It is the only place in the solar system besides Earth where you can find permanent ice caps. These two Martian ice caps are primarily made of frozen water… but not only! During the winter season, the poles permanent bulk of “water ice” are covered by a seasonal layer of frozen carbon dioxide (commonly known as dry ice).

How come? Similar to Earth, during each pole’s respective winter, these ice caps experience continuous darkness for several months. The temperature becomes so cold (freezing point is -126°C !) that carbon dioxide in its atmosphere freezes and falls onto the ground, forming layers of dry ice. In the summer when the sun returns and temperatures warm, the dry ice begins sublimating back into the atmosphere. At the North pole almost all the dry ice turns back into gas and the ice caps shows its water ice, while a layer of frozen carbon dioxide always remains at the South pole. Seasonal variations can thus be observed like those on Earth.

Martian North (left) et South (right) poles [Credit: NASA ]

The northern ice cap on Mars is much bigger than the southern one. It is about 1,000 kilometers wide (roughly the width of Greenland at its widest point) while the South pole is only 350 kilometers in diameter. Yet… they both contain the same amount of ice! If all of this ice was to melt, Mars’ surface would be covered by an ocean that was 18 meters deep. They are thus the currently largest known water reservoirs on the planet.

But… what are these spiral forms on Mars’ ice caps?!

The ice caps at both Martian poles show spiral throughs. According to the ESA, these unique features are the result of strong winds that spiral at the surface of the ice caps due to the same Coriolis effect that exists on Earth. This makes every fluid rotate to the right in the North Hemisphere and to the left in the South Hemisphere.

In the North Pole, one of these throughs, called Chasma Boreale, is particularly big. This 100-kilometer-wide and 2-kilometer-deep canyon roughly cuts the Northern Martian ice cap in half.

Chasma Boreale on the Northern ice cap [Credit: NASA ]

Drilling ice cores on Mars?

The seasonal melting and accumulation of ice occurs while dust deposits, which explain why both Martian polar caps exhibit layered features. They are thus composed of layers of ice mixed with dust (in the scientific jargon, Mars ice caps are called “Polar Layered Deposits”). As for ice cores on Earth, information about the past climate of Mars might be “trapped” in these dust layers. These are essential if we want to find proof of a time when liquid water existed on Mars! Unfortunately, ice cores have not been drilled… yet!

Layers in North Martian Ice Cap (The more dust, the darker the surface) [Credit: NASA/JPL/University of Arizona ]

Further Reading

Edited by David Rounce


Violaine Coulon is a PhD student of the glaciology unit, at the Université Libre de Bruxelles (ULB), Brussels, Belgium. She is using a numerical ice sheet model to investigate the dynamics and stability of the Antarctic Ice Sheet for the past 1.5 million years.


Image of the Week – Searching for clues of extraterrestrial life on the Antarctic ice sheet

Fig. 1: A meteorite in the Szabo Bluff region of the Transantarctic mountain range, lying in wait for the 2012 ANSMET team to collect it [Credit: Antarctic Search for Meteorites Program / Katherine Joy].

Last week we celebrated Antarctica Day, 50 years after the Antarctic Treaty was signed. This treaty includes an agreement to protect Antarctic ecosystems. But what if, unintentionally, this protection also covered clues of life beyond Earth? In this Image of the Week, we explore how meteorites found in Antarctica are an important piece of the puzzle in the search for extraterrestrial life.


Meteorites in Antarctica

Year after year, teams of scientists from across the globe travel to Antarctica for a variety of scientific endeavours, from glaciologists studying flowing ice to atmospheric scientists examining the composition of the air and biologists studying life on the ice, from penguins to cold-loving microorganisms. Perhaps a less conspicuous group of scientists are the meteorite hunters.

Antarctica is the best place on Earth to find meteorites. Meteorites that fall in this cold, dry desert are spared from the high corrosion rates of warmer, wetter environments, preserving them in relatively pristine condition. They are also much easier to spot mainly due to the contrast between their dark surfaces on the white icy landscape (see our Image of the Week), but also because the combination of Antarctica’s climate, topography and the movement of ice serves to concentrate meteorites, as if lying in wait to be found.

The targeted search for meteorites has taken place annually since the late 1960s, leading to the recovery of over 50,000 specimens from the continent, and counting. The most prolific of these search teams is the US-led Antarctic Search for Meteorites ANSMET), which lay claim to over half of these finds. Comprising only a handful of enthusiasts, this team camps out on the slopes of the Transantarctic Mountains for around 6 weeks hunting for meteorites. The finds include rocks originating from asteroids, the Moon and Mars.

 

Evidence of life in a meteorite?

There has long been a link between meteorites and the potential for life beyond Earth. Perhaps the most famous, or rather infamous, meteorite found in Antarctica is the Alan Hills 84001 meteorite (ALH84001). Found by the 1984 ANSMET team, this meteorite was blasted from the surface of Mars some 17 million years ago as a result of an asteroid or meteorite impact, falling to Earth around 13,000 years ago. This piece of crystallised Martian lava is roughly 4.5 billion years old. The reason for its infamy is the widely publicised claim made a decade after its discovery that it harbours evidence of Martian life [McKay et al 1996]. Specifically, application of high resolution electron microscopy unearthed microstructures comprising magnetite crystals that looked, to the NASA scientist David McKay and his team, like fossilised microbial life, albeit at the nanoscale (see Fig. 2).

Fig.2: A nanoscale magnetite microstructure that was interpreted as fossilised microbial life from Mars [Credit: D McKay (NASA), K. Thomas-Keprta (Lockheed-Martin), R. Zare (Stanford), NASA].

Such a finding of evidence for extraterrestrial life has huge implications for the presence of life beyond Earth, a subject that has captivated humankind since ancient times. This extraordinary claim made headline news across the globe. It even gained acknowledgement by the then US president Bill Clinton. In the words popularised by Carl Sagan, “extraordinary claims require extraordinary evidence”, and this one garnered considerable controversy that endures today. At the time, there was no known process that did not involve life that could result in these types of structures. Subsequent research, triggered by this claim, has since indicated otherwise. The debate rolls on, and it seems we will never really know whether the crystals structures are fossils of Martian life or not, with no conclusive evidence on either side of the argument. Nevertheless, the interest and attention gained through this story kick-started a flurry of hugely successful Mars exploration missions, as well as reinvigorated the search for life beyond Earth.

 

Meteorites as microbial fuel

The ALH840001 is an unusual connection between meteorites and the search for extraterrestrial life. Much subtler, but more wide-reaching, is the potentially important connection between organic-containing meteorites and the existence of life elsewhere. The chondrite class of meteorites originates from the early solar system, specifically from primitive asteroids that formed from the accretion of dust and grains. They are the most common type of meteorite that falls to Earth, and contain a wide array of organic compounds, including nucleotides and amino acids, the so-called building blocks of life. In addition, a number of organic compounds that reside in these meteorites are also common on Earth, and are known to fuel microbial life by serving as a source of energy and nutrients for an array of microorganisms [Nixon et al 2012]. These meteorites have fallen to Earth and Mars for billions of years, since before the emergence and proliferation of life as we understand it. A significant quantity of these meteorites, and the organic matter contained within them, has therefore accumulated on Mars. In fact, owing to the thinner atmosphere of Mars, a larger quantity is expected to have accumulated there than on Earth, and with more of its organic content intact. It is a therefore a distinct possibility that these meteorites may play an important role in the emergence, or even persistence, of life on Mars, if such life has ever existed [Nixon et al 2013].

The search for life on Mars is very much an active pursuit. As we continue this search using robotic spacecraft, such as NASA’s Curiosity rover and the upcoming European Space Agency’s ExoMars rover, we seek to better define whether environments on Mars are habitable for life. But our understanding of habitability on Mars and beyond is defined by our knowledge of the limits of life here on Earth, such as the microbial lifeforms that can make a living on and under the Antarctic ice sheet (see this previous post), but also in terms of the chemical energy able to support life. The search for meteorites on Antarctica has an important role to play here, and long may the hunt continue.

 

References and further reading

Edited by Joe Cook and Clara Burgard


Sophie Nixon is a postdoctoral research fellow in the Geomicrobiology group at the University of Manchester. She completed her PhD in Astrobiology in 2014 at the University of Edinburgh, the subject of which was the feasibility for microbial iron reduction on Mars. Sophie’s research interests since joining the University of Manchester are varied, focussing mainly on the microbiological implications of anthropogenic engineering of the subsurface (e.g. shale gas extraction, nuclear waste disposal), as well as life in extreme environments and the feasibility for life beyond Earth. Contact: sophie.nixon@manchester.ac.uk

Image of the Week — Microbes munch on iron beneath glaciers

Image of the Week — Microbes munch on iron beneath glaciers

The interface between a glacier and its underlying bedrock is known as the subglacial zone. Here lie subglacial sediments, the product of mechanical crushing of the rock by the glacial ice. Despite their lack of sunlight, nutrients and oxygen, subglacial sediments host active and diverse communities of microorganisms.

What we (don’t) know about subglacial microorganisms

The past few decades have seen major advances in our understanding of these communities, including the role these microbes play in the chemical breakdown of underlying bedrock (chemical weathering reactions). It is now known, for example, that microorganisms in subglacial systems are involved in pyrite oxidation and it certainly seems that bedrock mineralogy influences the composition of these microbial communities.

However, most studies to date have focussed on the biogeochemical cycling of sulfur and nitrogen in these systems. Consequently, the microbial mediation of iron cycling in subglacial systems remains poorly understood, despite the importance of iron in ocean fertilisation and other downstream environments. For instance, phytoplankton in the open ocean are often limited by the amount of iron available, so fluxes of iron to the oceans from glaciers and ice sheets are an important contribution to ocean productivity.

A new study about subglacial iron

In a new paper published in Biogeosciences, we investigate microbial iron reduction in subglacial sediments. Microorganisms that carry out this metabolism are able to harness energy from the reduction of oxidised iron minerals (such as ferrihydrite and other iron oxides).

We wanted to know two things:

  1. are these microorganisms present and alive in subglacial sediment?
  2. are these microorganisms adapted to the cold conditions of these environments?

 

To achieve this, we set up experiments in which we ‘teased out’ the microorganisms that make a living from iron reduction, and measured their rates of iron reduction at two different temperatures: 4°C (blue line in the figure) and 15°C(red line). These temperatures were chosen since truly cold-loving (‘psychrophilic’) microorganisms grow optimally at temperatures below 10-15°C, whereas those that tolerate cold temperatures (‘psychrotolerant’) prefer to grow in higher temperatures.

Microorganisms that can use iron to make a living are amongst the most plausible life to exist on Mars

We found that active iron-reducing microorganisms were present in all of our subglacial sediment samples, which spanned glaciers in the High Arctic, European Alps and Antarctica, and that in almost all cases rates of iron reduction were higher at the lower temperature tested. To get an idea of which microorganisms were carrying out this process, we looked at the DNA from our experiments to identify the microbes present. We found that the microorganisms using iron in our experiments were largely the same, suggesting that the same key players are active in these types of environments worldwide. Overall our paper suggests that microbial iron reduction is widespread in subglacial environments, with implications for the availability of iron for other biogeochemical processes downstream. Subglacial environments are thought to be similar to potentially habitable environments on Mars, and microorganisms that can use iron to make a living are amongst the most plausible life to exist on the Red Planet, now and in the past. Our work therefore strengthens the hypothesis that similar environments beyond Earth could harbour this type of life.

Edited by Sophie Berger


Sophie Nixon is a postdoctoral researcher in the Geomicrobiology group at the University of Manchester. She completed her PhD in Astrobiology in 2014 at the University of Edinburgh, the subject of which was the feasibility for microbial iron reduction on Mars. One essential task in the search for life on Mars and beyond is defining the limits of life in extreme environments here on Earth. It was during her PhD that this study was carried out in collaboration with researchers at the University of Bristol, where Sophie gained her MSci in Geographical Sciences. Sophie’s research interests since joining the University of Manchester are varied, spanning the microbiological implications of anthropogenic engineering of the subsurface (e.g. nuclear waste disposal, shale gas extraction), as well as life in extreme environments and the feasibility for life beyond Earth. 

Glaciers on Mars

Glaciers on Mars

“I did not know that there is water on Mars!” This a sentence I hear surprisingly often when I talk about glaciers on Mars. In fact, it has been known for some time that water exists in the form of ice and water vapour on the planet. For example, water ice layers several kilometres thick cover the Martian poles, and the ground close to the Polar Regions has permafrost patterns very similar to what we see on Earth.

The glaciers on Mars were discovered in the 1970s on images from the Viking missions. From the images it was evident that features made up of a soft, deforming material existed in some parts of the planet. At the time, it was suggested that the features might consist of a mixture of water ice, CO2 ice or perhaps mud.

More than 10,000 water ice bodies (blue dots) have been found between 30 and 50 degrees (blue lines). Credit: Mars Digital Image Model, NASA/J. Levy/Nanna Karlsson

More than 10,000 water ice bodies (blue dots) have been found between 30 and 50 degrees (blue lines). Credit: Mars Digital Image Model, NASA/J. Levy/Nanna B. Karlsson

In 2005, NASA launched the satellite Mars Reconnaissance Orbiter that carried amongst other instruments the SHARAD (SHAllow RADar) sounder. The instrument emitted radar waves that could penetrate the surface of the planet, and return information on what was below the dusty surface. The mission proved successful and – amongst many other discoveries – the SHARAD measurements showed that the glaciers consist of more than 90% water ice .

We now know the composition of the glaciers but many questions remain. One extremely interesting observation is the fact that the glaciers are only found in particular latitude bands: between 30 and 50 degrees on both hemispheres. A recent study has mapped more than 10,000 features in these latitudes. In other words, the glaciers are much more abundant than initially thought, but why are they there in the first place? The answer is probably to be found somewhere in Mars’s past. More than 5 million years ago, the amount of solar insolation at the poles of Mars was dramatically different compared to today. Models have shown that during this time water ice at the poles would have been unstable and possibly migrated to the midlatitudes. When the climate changed, again the water migrated back to the poles. The glaciers could therefore be remnants of a past, large ice sheet.

CTX imagery of a glacier surrounding a central massif. Credit: CTX/JMars.

CTX imagery of a glacier surrounding a central massif. Credit: CTX/JMars.

How much water do the glaciers contain then? To answer this question, we can use knowledge of glaciers on Earth. A glacier is essentially a big chunk of ice, and when it flows, it obtains a shape that tells us something about how soft the ice is. Water ice moves and deforms in a certain way, and the slope of the surface of a glacier therefore reveals information about the bed under the glacier. Looking at images of the Martian surface, we can see where the glaciers are, and from the Mars Orbiter Laser Altimeter we know the surface elevation. This allows us to setup models for how the ice behaves on Mars.

Combining the models with the radar measurements and maps of the glaciers, it turned out that the glaciers contain more than 150 thousand cubic kilometres of ice. This amount of ice may cover the surface of the planet in a 1.1 metres thick ice layer.

Dust covered water ice close to the south pole and white CO2-ice.

Dust covered water ice close to the south pole and white CO2-ice. Credit: ESA/DLR/FU Berlin.

If you want to know more about glaciers on Mars check out my recent paper published in Geophysical Research Letters. You can also meet me at the EGU General Assembly next week and listen to my talk at 8:30am, Wednesday the 15th of April in Room R13 (Session CR6.1Modelling ice sheets and glaciers).