This page was contributed by Dr Frances Butcher from Sheffield University.
There are glaciers on Mars?!
Just as on Earth, glaciers on Mars come in lots of different shapes, sizes, and settings. Studying glaciers on Mars is important for several reasons:
- Glaciers on Mars were formed under some of the most recent major climate changes on the planet, so they can teach us about the recent evolution of Mars’ climate and atmosphere.
- When humans eventually travel to Mars, they’re unlikely to be able to take all of the water they need with them. Glaciers on Mars could provide important in situ water resources for future human exploration of the planet1.
- Mars’ surface is bombarded by harsh radiation from the Sun (because of the very thin atmosphere), which makes it inhospitable. If microbial life exists on Mars, the beds of glaciers on Mars could provide protected environments for microbes to survive.
You can explore Mars yourself on Google Mars! You can also view Mars in Google Earth, and explore the Martian ice caps.
Polar ice on Mars
Mars has extensive polar ice caps made mostly of water ice, which are up to ~3.7 kilometres thick2. The polar caps contain a combined volume of water ice similar to the Greenland Ice Sheet on Earth3.
Mars’ south polar cap also has a thin (8–10 m thick4), permanent layer of carbon dioxide ice on top. This is because temperatures at Mars’ south pole are so cold that carbon dioxide (which makes up 95% of Mars’ thin atmosphere) can remain frozen on the surface throughout the year.
Carbon dioxide ice is also deposited as frost on top of the north polar cap in winter. It turns back to gas in northern spring because temperatures at the north pole are warmer than at the south pole.
There are also polar glaciers beyond the margins of the polar ice caps. Korolev crater is an impact crater which is filled with ice.
Mid-latitude glaciers on Mars
Mars also hosts glaciers in its mid-latitudes. They are thought to be made up of nearly pure water ice, covered in a thin (less than 10 m thick) blanket of atmospheric dust and debris from nearby hillslopes5–7.
Mars’ mid-latitude glaciers are thought to be most similar to cold-based debris-covered glaciers in the Dry Valleys of Antarctica. Cold-based glaciers are frozen to their beds, with very little meltwater being produced at the ice surface or underneath the glacier. It is thought that Mars’ mid-latitude glaciers are currently completely frozen e.g., 9–11 under the extremely cold present-day climate conditions. However, there is some evidence for extremely rare, localised melting of these glaciers in the past e.g., 9–11.
The collective term for mid-latitude features interpreted as debris-covered glaciers on Mars is ‘viscous flow features’. This might seem like a rather dull name for such exciting features! Why don’t we just call them debris-covered glaciers? We’ll return to this question after we’ve explored the different types of viscous flow features in more detail.
Valley glaciation on Mars
There are two categories of viscous flow features on Mars which resemble valley glaciers: ‘glacier-like forms’ and ‘lineated valley fill’. The main differences between these categories are their sizes.
Glacier-like forms11 are described in our introduction to glaciers on Mars. They are small (typically a few kilometres long) features confined to valleys, and originate in alcoves on mountain sides. Their termini are often bounded by moraine-like ridges12,13.
Lineated valley fills14–16 are typically larger features (up to ~100 kilometres in length and tens of kilometres wide) occupying large, deep troughs in the Martian surface. These troughs are often tectonic in origin, for example graben or rift valleyse.g., 10.
Lineated valley fills have spectacular flow lines on their surfaces.
Glaciation of lowland plains on Mars
Many valley glaciers on Mars flow out of valleys and onto lowland terrain. Where they exit the valleys, they spread out into lobes which are unconfined by topography. This is similar to ‘piedmont’ glaciers on Earth.
‘Lobate debris aprons’ e.g., 7, 17 are a type of unconfined glacier on Mars which form piedmont-like lobes. Some lobate debris aprons are fed by lineated valley fills and glacier-like forms upslope.
Others are not fed by glaciers in upslope valleys. Instead, they originate at steep headwalls, and extend over neighbouring lowland plains.
The term ‘lobate debris apron’ is a little outdated; when lobate debris aprons were discovered, it was thought that they were made mostly of debris mixed with ice17. More recently, ground-penetrating radar data from orbiting satellites have shown that they are most likely to be debris-covered glaciers made of >80% water ice5–7.
Impact crater glaciation
A very common type viscous flow feature in Mars’ mid-latitudes is called ‘concentric crater fill’. Concentric crater fills exist within (and often completely infill) impact craters e.g., 18. They often have roughly circular flow lines on their surfaces.
Glaciation of impact craters might seem very strange, but there are glaciated impact craters on Earth too. Impact craters in Canada and Scandinavia were covered by the continental-scale ice-sheets of the last glacial maximum.
Zoom around the glacially-streamlined landscape of these impact craters in Quebec, Canada. The lakes which occupy these craters today are called Lac Wiyâshâkimî (or Clearwater Lakes in English). During the last glacial maximum, the craters were covered by the North American Ice Sheet. The flow of the ice sheet modified the topography of the craters, streamlining their rims and the peak ring (a ring of mountains which commonly form within large impact craters) in the western crater. Can you work out which way the ice flowed? You will find some clues in this article about drumlins.
A 31 kilometre-wide impact crater was recently discovered beneath Hiawatha glacier at the margin of the Greenland ice sheet19.
The reason that impact crater glaciation is so much more common on Mars than on Earth is simply because impact craters are much more abundant on Mars.
Unlike Earth, Mars does not have plate tectonics, so its crust has not been recycled. This means that Mars’ surface bears the scars of more than 4 billion years of geological processes, including impact cratering.
The Earth’s crust is relatively young. It has been refreshed by plate tectonics, which draws down old crust (and with it, impact craters) in subduction zones, and produces new crust via sea floor spreading.
Mars also lost a lot of its protective atmosphere early in its history. This meant that meteorites were more likely to reach the surface and form impact craters before they could burn up in the atmosphere.
How old are glaciers on Mars?
Existing mid-latitude glaciers on Mars have been dated to be between a few million20 and hundreds of millions of years old21. Some may even be as old as 1 billion years15!
Mars’ polar ice caps are probably younger. Most of the North polar cap is thought to have accumulated within the last 5 million years22.
From the perspective of Earth, this seems very old. However, in terms of Mars’ geologic history, geomorphic activity within the last 1 billion years is considered to be recent. This is because most major geologic activity on Mars slowed significantly more than 3 billion years ago.
The mass balance of mid-latitude glaciers on Mars
Glacier ‘mass balance’ is the balance of the accumulation and loss of glacial ice. The past and present mass balance of mid-latitude glaciers on Mars is an area of ongoing research.
The glaciers are not thought to be accumulating ice in the present day. We have not been observing the glaciers for long enough to detect whether they are losing ice, or whether they are still flowing. If they are flowing, the cold climate conditions and low gravity means that flow is probably extremely slow.
If the mid-latitude glaciers had no debris cover, the current atmospheric pressure on Mars (which is just 0.6% of atmospheric pressure on Earth) would cause the ice to undergo sublimation.
Sublimation is the process where a solid turns straight into a gas without going through the liquid phase.
Watch sublimation of water ice in action! In this video water-ice snow is placed into a low-pressure chamber, where the pressure is similar to atmospheric pressure on Mars. The snow turns into a gas without melting. The presenter then returns the chamber to Earth’s atmospheric pressure and you can see the snow begin to melt!
Watch especially from 3 min 58 seconds to 6 min 22 seconds.
Exposed ice at the Martian poles is less prone to sublimation despite the fact it is not debris-covered. This is because the temperatures at Mars’ poles are so extremely cold (reaching -140°C at the winter pole).
The debris cover on mid-latitude glaciers on Mars has probably slowed the sublimation of the underlying ice significantly, and it could be thick enough to have halted sublimation altogether.
Some of the smaller viscous flow features on Mars might have lost much of their ice content. Those features could be more similar to rock glaciers in the present day. Rock glaciers can look similar to debris-covered glaciers, and are made mostly of debris with small amounts of ice between the rocks. Debris-covered glaciers can evolve into rock glaciers as their ice content is depleted.
Why do we use the term ‘viscous flow feature’?
Viscous flow feature is a ‘non-genetic’ term. This means that, unlike ‘debris-covered glacier’, it does not state a process by which the features formed.
It is important that we do not formally give features names which confidently state their formation process until this process has been verified beyond reasonable doubt.
Currently, the interpretation that viscous flow features are debris-covered glaciers is based solely on remote sensing data (mostly image and topographic data) from orbiting satellites.
Ground-penetrating radar observations showing that viscous flow features are made mostly of glacial ice are becoming more common, but are currently limited to a relatively small number of features5–7.
The existing evidence that most viscous flow features are debris-covered glaciers is strong. However, ground-based observations (e.g. with landers or rovers) are probably required to prove this beyond reasonable doubt.
However, even when ground-based observations are possible, we are unlikely to be able to visit every feature individually, so we may still be uncertain about whether the features are all the same. Are they all debris-covered glaciers, or are some more similar to rock glaciers? The term ‘viscous flow feature’ is probably here to stay!
About the Author
Dr Frances Butcher is a planetary scientist researching glaciers on Earth and Mars. She completed her PhD entitled ‘Wet-Based Glaciation on Mars’ at the Open University (UK) in 2019. She is currently a member of the European Research Council (ERC) funded PALGLAC project at The University of Sheffield (UK), using glacial landforms on Earth to reconstruct the dynamics of the former Scandinavian Ice Sheet. Frances has been involved in preparations for the ESA-Roscosmos ExoMars (‘Rosalind Franklin’) Rover mission, which launches to Mars in 2022.
You can follow Frances on Twitter @fegbutcher
You can also follow the PALGLAC project @palglac
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