Today was supposed to have been the last day at the cancelled 51st annual Lunar & Planetary Science conference. As such, only a half day of presentations had been scheduled in order to give participants the option of returning home sooner.
While many of the abstracts of the planned-but-now-cancelled presentations were on subjects important to the scientists but not so interesting to the general public, two sessions, one on Martian buried glaciers/ice and a second focused on Mercury, would have made the day very worthwhile to this science journalist, had I been there.
The map above, from the first abstract [pdf] of the Mars session, might possibly epitomize our present knowledge of ice/glaciers on Mars. It provides an update of the continuing survey of ice scarps in the high mid-latitudes of Mars (see the most recent post on Behind the Black from February 12, 2020). Clearly, the more they look, the more they find of these ice scarps, cliff faces with visible exposed pure ice layers that will be relatively easy to access.
But then, finding evidence of some form of buried ice on Mars is becoming almost routine. Of the thirteen abstracts in this Mars session, ten described some sort of evidence of buried ice or glaciers on Mars, in all sorts of places, with the remaining three abstracts studying similar Earth features for comparison. The scientists found evidence of water ice on the top of one of Mars’ largest volcanoes (abstract #2299 [pdf]), in faults and fissures near the equator (#1997 [pdf]), in the eastern margin of one of Mars’ largest deep basins (#3070 [pdf]), in Gale Crater (#2609 [pdf]), in the transition zone between the northern lowlands and southern highlands (#1074 [pdf]), and of course in the northern mid-latitude lowland plains (#2648 [pdf] and #2872 [pdf]).
The results tell us not that there is water ice on Mars, but that it is very plentiful, and that its presence and behavior (as glaciers, as snowfall, and as an underground aquifer) make it a major factor in explaining the geology we see on Mars. I’ve even begun to get a sense that among the planetary scientists researching Mars there is an increasing consideration that maybe ice formed many of the river-like features we see on the surface, not flowing water as has been assumed for decades. This theory has not yet become dominate or even popular, but I have been seeing mention of it increasingly in papers, in one form or another.
If this possibility becomes accepted, it would help solve many Martian geological mysteries, primary of which is the fact that scientists cannot yet explain how water flowed as liquid on the surface some time ago in Mars’ long geological history, given its theorized atmosphere and climate. If ice did the shaping, then liquid water (in large amounts) would not be required.
Now, on to the Mercury session.
There were several basic topics covered, as follows:
- Mercury’s interior structure is not really understood. They think its mantle is thin and its core is large, but as one abstract [pdf] noted, “the structure of Mercury’s interior remains ambiguous and still leaves room for speculation.” The carton model to the right comes from that paper, and is a best guess based on present knowledge, with many uncertainties.
- Though Mercury and the Moon appear superficially the same, there are some fundamental differences. For one, Mercury is darker, for reasons that are not understood. Two abstracts (#1859 [pdf] and #2873 [pdf]) looked at whether carbon in some form could explain the difference.
- Another abstract [pdf] did a census of the 104 volcanic vents on the planet, thought to be evidence of explosive volcanism some time in the relatively recent geological past. Interestingly, 82% of these vents are found in craters, and in general they are not associated with Mercury’s mare volcanic plains.
- New research [pdf] into the possibility of ice in the permanently shadowed craters at Mercury’s poles focused at one polar crater, Ensor, finding that instead of ice the crater might contain “complex organic volatile compounds.” (This is not life, but complex molecules that include carbon.)
- A comparison [pdf] of the craters and their degradation over time on the Moon and Mercury found that the regolith on Mercury is probably thicker, by as much as 8 to 20 meters.
Finally, there is the image to the right, taken from one abstract [pdf] researching the formation of what scientists call hollows on Mercury. As the abstract notes:
Hollows are irregularly-shaped small rimless shallow depressions on Mercury that are usually associated with high-reflectance haloes. Hollows are likely formed by loss of volatile-bearing phase in surface materials via possibly sublimation process, and they are possibly still activate
In other words, some material in the ground changes from a solid to a gas (sublimates), creating voids that eventually collapse to create the hollow as well as the bright surface that surrounds it.
In the image, the arrows in B indicate the high-reflectance halo on the hollow rim. In C the arrows indicate the interior base of the crater wall where these hollows are found.
The abstract also notes that “there is no consensus in previous studies about the possible nature of volatiles that formed the hollows.” The present paper does not solve this question either, though it provides further constraints that might help solve it eventually.
With this report, the non-existent Lunar & Planetary Conference has ended (even though it never really started). I will likely follow up with the scientists for some of these stories to get a bit more background and information. Some of these abstracts absolutely demand it, and would have gotten that attention now if the world had not gone bonkers over a virus that I will once again predict will become just another variation of the flu.
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