More About Mars Glaciers

I posted previously about the announcement that buried glaciers had been discovered on Mars, but now I’ve had time to actually take a look at the article in Science. The important point of the article is not that these formations were discovered (we’ve actually known about them for some time) but that, using radar on the Mars Reconaissance Orbiter, scientists were able to penetrate the surface of these mysterious glacier-looking things and prove that they are mostly ice!

You may be wondering how you could have a big, lobate, flowing tongue of stuff that isn’t mostly ice. Well, all you need is something viscous to flow. A pile of rocks, with just a tiny bit of ice holding them together and lubricating the flow can mimic the shape of a glacier of pure ice. Conveniently enough, I got interested in these last year when I was taking a geomorphology class, and found some pictures of terrestrial examples in the Andes with Google Earth:
cerro-catedral-rock-glacier

You can see the lobate flows oozing their way down from the peaks, but in this case, you’re looking at something that is almost entirely rock. Many people thought that the glaciers that people were seeing on Mars were similar, but there was no way to test this until MRO got there with its radar sounder, SHARAD. Radar waves bounce off of rock, but are quite good at penetrating ice. So, when MRO flew over the glaciers, the scientists bounced radar off the glaciers and saw this:

sharad_glaciers

This shows along the top what the surface would look like if it was just made of rock, and then it shows the actual data below. You can see that the lobes of “stuff” have a radar reflection at their surface, but some of the radar penetrates and bounces off of another boundary beneath the surface. This is showing that some of the radar reflects off of the surface but some travels down through the ice until it hits solid ground underneath. Rock glaciers wouldn’t do this, but glaciers of almost pure ice would!

The paper has a very nicely written concluding paragraph that I will post here, with slight annotations. It explains why the glaciers are there and why they are significant:

Why would such large quantities of snow and
ice accumulate in the eastern Hellas region in
particular? Over time scales of millions of years,
Mars undergoes large changes in spin-axis obliquity (tilt), forcing changes in insolation (sunlight energy that reaches the surface), and hence
in climate and the subsequent distribution of
ice. Climate simulations performed with
a model that includes the current water cycle but
assumes an obliquity of 45° predict snow accumulation
in the eastern Hellas region from a
south polar water source that operates efficiently
at the southern summer solstice, when the southern
polar cap releases large amounts of water
vapor. This vapor moves northward and is deflected
by cold air moving southward from the
Hellas basin; the subsequent cooling causes strong
condensation and precipitation in the area of the
LDAs (Lobate Debris Aprons), which we have shown to contain
primarily water ice. We therefore conclude that
these deposits harbor large quantities of water ice
derived from high-obliquity epochs, now concealed
beneath a thin protective layer. This ice
survives from climatic conditions markedly different
from today’s and is potentially accessible
to future landed missions, not only for scientific
study but as a resource to support exploration.

Explore posts in the same categories: Current Research, MRO, NASA, Pictures, Water on Mars

One Comment on “More About Mars Glaciers”

  1. David Says:

    This discovery sustain some old find´s.

    MOC (Mars Global Surveyor Camera) Orbiter images of lineated valley fills and lobate debris aprons show that the surface of this features are practically uncratered, indicating likely emplacement and formation within the past several million years. With this method, the lobes of Olympus Mons were dated to be polygenetic with ages ranging between 280-130, 60-20, and -surprisingly- 4 million years and younger.
    However at current Mars surface temperatures, and very low accumulation rates of material, flow rates large ice masses would be so slow, that they could not be younger then 1 to 10 millions of years, but still much older then the crater counting let conclude. But assuming higher past temperatures in geologically speaking recent times, a young age became more convincing.
    Overlapping tongues seen on some lobes even let assume that they were periodically active, implying possibly glacial and interglacial periods on Mars, driven by the steep tilted axis of Mars (15-35°).

    The distribution of the presumed activ and relict rockglaciers seem to support this hypothesis, they only occur in a narrow belt of 30 to 50° of latitude on both hemisphere, region that in past “passed trough” the climatic zone that enables the formation of great amounts of ice and activity of rockglaciers.

    N.B.

    Georadar measurements provided information on the internal structure and thickness of (some) rockglacier. The data indicate that some rockglacier have only a debris layer. Below the debris layer numerous, well developed reflectors are visible indicating the presence of shear planes in the frozen body of the rockglacier, which according to ice exposure in the upper part is composed of coarse (glacier) ice with numerous thin debris layers parallel to the banding. A thin sediment layer (?lodgement till) may be present at the base of the rockglacier.

    Internal structure and ice exposure clearly indicate that ice-cored rockglaciers developed from a debris-covered cirque glacier. It is suggested that the glacier has developed from a small cirque glacier during retreat trough inefficiency of sediment transfer from the glacier ice to the meltwater.

    DEGENHARDT Jr., J.J. & GIARDINO, J.R. (2003): Subsurface investigation of a rock glacier using ground-penetrating radar: Implications for locating stored water on Mars. Journal of Geophysical Research, 108: 8036-8053
    GASSELT, S. (2007): Cold-Climate Landforms on Mars. PhD University of Berlin
    MAHANEY, W.C.; MIYAMOTO, H.; DOHM, J.M.; BAKER, V.R. & CABROL, N.A. (2007): Rock glaciers on Mars: Earth-based clues to Mar’ recent paleoclimatic history. Planetary and Space Science 55: 181-192
    Neukum,G.; Jaumann, R..; Hoffmann, H.; Hauber,H.; Head, J. W.; Basilevsky, A. T. ; Ivanov, B. A.; Werner, S. C.; van Gasselt, S.; Murray, J. B.; McCord T. & The HRSC Co-Investigator Team (2004): Recent and episodic volcanic and glacial activity on Mars revealed by the High Resolution Stereo Camera. Nature , 432: 971-979
    SQUYRES, S.W. (1979): The distribution of lobate debris aprons and similar flows on Mars. Journal of Geophysical Research 84: 8087-8096


Comments are closed.


%d bloggers like this: