Re: Phoenix color photos



Pat Flannery wrote:
Newest goodies from the north polar region of Mars: http://www.jpl.nasa.gov/news/phoenix/main.php
Soil color looks very similar to what the two MERs found at their landing sites.
Tan/orangish iron oxide soil as expected.
Far more small rocks in the soil than at either of the MER sites. Small-scale rough terrain quite different than one would find on Earth outside of an area of severe volcanic action unaltered by any sort of modifying via weathering, glaciers, or rivers.
On Earth, you can find soils like this in the barren areas of the northern African rift valley, as well as the volcanic fields that sit in the western areas of the Arabian Sinai, and that are a extensions of it.

Which is surprising - at both of Earth's poles wind speed can become very high indeed (over 100 mph at the south pole), and you'd expect the rocks to get worn down into a more rounded form by slamming into each other over tens of thousands of years.... with the far lower atmospheric pressure being balanced off to some extent by the lower gravity on Mars that would get the rocks moving round.. This might indicate that the rocks in the photo are fairly dense and heavy, and therefore not prone to getting moved around even by very high velocity Martian winds.
In short, more like basalt or obsidian than pumice.
Yet they lie around on the surface - indicating that their average mass is lower that the soil beneath them - so maybe they are of middle weight - lighter than the soil, but not so light that the wind can blow them around.
If I were to take a guess at this right now, I'd say that most of those small rocks that Phoenix is seeing are ejecta from huge volcanic eruptions. They're porous, but not so porous and lightweight as pumice.
What makes pumice so lightweight is that the water in the magma that forms it expands into superheated steam as its ejected from the volcano, turning it into a rock analogy of Styrofoam.... like popping popcorn as its shell ruptures and the superheated water in it expands - simultaneously expanding and cooking the interior material of the corn kernel.
Without water as an integral part of its make-up, Martian magma may behave completely differently from its Earthly relative.
The "blueberries" have already been pretty much tracked down as meteorite splash that cooled into spheres as it fell through the Martian atmosphere.
These rocks that Phoenix has seen are rough, so that pretty much removes them from the meteorite-splash created type.

Pat
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Relevant Pages

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