[X] My Assistant

[Guest_BruceMoomaw_*]

This is inevitably a subjective list of the stuff that happened to strike me, personally, as especially interesting -- but here goes:

#2401: MER-B's analysis of the composition of the "cobblestones" that have intrigued the scientists for so long. They turn out to be varying mixtures of the sulfate-processed stuff seen elsewhere with less modified basalt, suggesting that they are local crater ejecta from lower layers of the deposit that were exposed to less acidic water.

#1312: Some nice sharp photos of Phobos by Mars Express from different angles.

#1592: Mars Express' OMEGA analyses of White Rock prove, once and for all, that there's nothing mineralogically unusual about it -- it's just indurated dust with nothing at all distinguishing it from the composition of the surrounding surface, and in particular no signs of water modification.

#2283: THEMIS maps of the southern polar cap's overlying CO2 layer suggest that -- contrary to MGS' earlier photos of the growing "Swiss cheese" holes -- it is actully GROWING in overall areal extent right now from one summer to the next, rather than shrinking due to slowly warming polar summers. Hard to know what to make of this.

#2376: Latest analyses of Mars Odyssey's ner-polar gamma-ray and neutron studies suggests that the dust layer over the near-solid underlying ice is no more than 4-6 cm thick, which "may present difficulties for those investigations interested in seeing gradients as a function of depth in the dry soil" -- and which my explain the mission's recent increase in emphsis on properly sampling and analyzing the permafrost itself, which has led to the addition of a rotating "ice shredder" on the rear of the sampling scoop. (See Deborah Bass' blog: http://phoenix.lpl.arizona.edu/features/we...eborah_bass.php .)

#2070, 1648 and 1739: the debate over the nature of the "Type 2" rock seen by MGS' TES covering the rocky parts of the nothern lowlands (as comapred to the regular "Type 1" basalt in the southern highlands) continues. Odyssey's GRS (#2070) shows a higher abudance of both potassium and thorium in the Type 2 rock, which suggests strongly that it is NOT just water-modified basalt, but some volcanic rock that was different in composition from the first, such as andesite, or at least basalt from "compositionally distinct mantle sources". However, OMEGA and THEMIS maps show VERY close local proximities of some deposits of Type 1 and Type 2 rock -- so close as to make it hard to see how they could be flows of seriously different types of lava, and thus suggesting again surface water modification of Type 1 basalt to make the Type 2 rock. This one has yet to be settled.

#2035: Strong visual evidence of eskers (ridges of sediment deposited by streams of meltwater underneath glaciers) in Isidis Planitia, "strongly indicative of a widespread ice cover across the basin at some stage in the past, even at the low latitude of Isidis Planitia."

#1242: Examination by TES and THEMIS of the phyllosilicate clay deposits found by OMEGA suggest that the clay component is actually quite dilute: "So far, it is not clear from unmixing results that the putative clay-rich deposits have significantly higher abun-dances of modeled clay minerals. Overall, these preliminary results suggest that the putative clay-bearing deposits are composed of igneous materials in large part. The thermal infrared spectral character of these deposits is not consistent with the expected spectral signature from extremely clay-rich materials such as bentonite layers...The deposits are not dominantly clay – they are com-posed of igneous materials with a limited clay component." Not all that much liquid water even under the most favorable circumstances in the Noachian?

#1342: Results of the latest survey of Mars for alluvial fans. 25 have now been found (still out of 40,000 craters), but there's a puzzle: "One fan has been found in the walls of Valles Marineris. It is the only fan not found originating in a crater rim. This is surprising because Valles Marineris provides an excellent topographic setting for the formation of alluvial fans (i. e. an abrupt topographic dictomy), so it might be expected that many more fans should be present. Future modeling and analysis will focus on why there are so few fans and why they form in specific locations along the canyon walls."

#2011: A suggestion that the dramatic (and recent) floods that have carved the features in Cerberus Plains may have been driven by the pressure of underground CO2, which should please Nick Hoffman no end.

Now, finishing up with a few abstracts from the new EGU, COSPAR and Astrobiology Science conferences:

http://www.cosis.net/abstracts/EGU06/06134/EGU06-J-06134.pdf and http://www.cosis.net/abstracts/EGU06/09673/EGU06-J-09673.pdf : Werner and Neukum say that an analysis of the size-frequency function of secondary craters proves that (contrary to William Hartmann) they are NOT making us serious fouling up our crater-rate estimates of the age of various terrains on the surfaces of other worlds by overestimating their age -- and particularly not for Mars. (Neukum, however, withdrew his paper from the EGU meeting for some reason.)

http://www.cosis.net/abstracts/COSPAR2006/...006-A-00693.pdf : Matt Golombek says again that the MER observations confirm that "a dry and desiccating environment similar to today’s has been active throughout the Hesperian and Amazonian (since ~3.7 Ga). By comparison, erosion rates estimated from changes in Noachian age crater distributions and shapes are 3-5 orders of magnitude higher and comparable to slow denudation rates on the Earth (>5 micron/yr) that are dominated by liquid water. The erosion rates from Gusev as well as those from Viking 1 and Pathfinder strongly limit this warmer and wetter period (recorded in the Meridiani evaporites and Columbia Hills) to the Noachian, pre-3.7 Ga and a dry and desiccating climate since."

http://abscicon2006.arc.nasa.gov/agenda-session.php?sid=23 , paper #34: Krasnopolsky has a whole series of interesting remarks regarding Martian methane. (He has, however, said many of the same things in two recent Icarus articles: http://www.ifa.hawaii.edu/~meech/NAIJC/pap...y_CH4onMars.pdf and http://www.ifa.hawaii.edu/~meech/NAIJC/pap...y_SO2onMars.pdf .)

[Guest_BruceMoomaw_*]

A few more interesting Mars abstracts from this year's meetings:

(1) MER-B's Mini-TES team ( http://www.lpi.usra.edu/meetings/lpsc2006/pdf/2021.pdf ) concludes from its deconvolution of the thermal-IT spectra of the Meridiani outcrop rock that it is indeed sulfates mixed with a large amount of amorphous silica and glass and the phyllosilicate nontronite -- confirming that the stuff mixed with the sulfates is indeed the dregs of basalt extensively modified by exposure to sulfuric acid, rather than unaltered basaltic mud being mixed in with the sulfates.

(2) P.E. Hintze says ( http://www.lpi.usra.edu/meetings/lpsc2006/pdf/2098.pdf ) that much of the disappearance of organics in Mars' surface soil may be attributable to the plasma produced by electrostatic glow discharges: "The high probability for dust interactions during Martian dust storms and dust devils, combined with the cold, dry climate of Mars, most likely results in airborne dust that is highly charged. Such high electrostatic potentials generated during dust storms on Earth are not permitted in the low-pressure CO2 environment on Mars; therefore electrostatic energy released in the form of glow discharges is a highly likely phenomenon. Since glow discharge methods are used for cleaning and sterilizing surfaces throughout industry, the idea that dust in the Martian atmosphere undergoes a cleaning action many times over geologic time scales appears to be a plausible one."

(3) The Mars Express HRSC team ( http://www.cosis.net/abstracts/EGU06/01915/EGU06-J-01915.pdf ) have seen big dust devils racing across the surface at 15-27 meters/sec, "not consistent with previous assumptions of the wind velocity at the martian surface (~5 m/sec)."

(4) The mole planned for inclusion on the Geophysical Experiment Package that is supposed to be left behind on the surface by the ExoMars rover -- to implant a chain of heat-flow sensors 5 meters deep -- is described in http://www.cosis.net/abstracts/EGU06/09633/EGU06-J-09633.pdf . Heaven knows whether it will actually work, but MEPAG considers Martian heat-flow measurements important if they can be done.

(5) The THEMIS team ( http://www.cosis.net/abstracts/COSPAR2006/...006-A-02673.pdf ) reports that "that the Martian crust, while dominated by basalt, contains a remarkable diversity of igneous materials whose range in composition -- from ultra-mafic basalts to granitoids -- rivals that found on the Earth" (although high-silica rocks are rare). They also note the vast variety of strange markings beneath the seasonal CO2 ice cap, "consistent with a translucent, impermeable CO2 ice cap that sublimates from the base, producing gas flow beneath the ice that erodes the channels and jets that erupt sand-sized grains through vents. These processes are unlike any observed on Earth. The vertical stirring of the polar-layered deposits by this process may have significantly altered the sedimentary record, and may complicate the interpretation of the sedimentary record as it relates to climate history."

[The Messenger]

A few more interesting Mars abstracts from this year's meetings:



(2) P.E. Hintze says ( http://www.lpi.usra.edu/meetings/lpsc2006/pdf/2098.pdf ) that much of the disappearance of organics in Mars' surface soil may be attributable to the plasma produced by electrostatic glow discharges: "The high probability for dust interactions during Martian dust storms and dust devils, combined with the cold, dry climate of Mars, most likely results in airborne dust that is highly charged. Such high electrostatic potentials generated during dust storms on Earth are not permitted in the low-pressure CO2 environment on Mars; therefore electrostatic energy released in the form of glow discharges is a highly likely phenomenon. Since glow discharge methods are used for cleaning and sterilizing surfaces throughout industry, the idea that dust in the Martian atmosphere undergoes a cleaning action many times over geologic time scales appears to be a plausible one."

Glow discharges are easy to create on Earth, using Mars-like atmospheres and dust grains. But to the best of my knowledge, we have not observed similar phenomenon on Mars. (yes?/No?)

(5) The THEMIS team ( http://www.cosis.net/abstracts/COSPAR2006/...006-A-02673.pdf ) reports that "that the Martian crust, while dominated by basalt, contains a remarkable diversity of igneous materials whose range in composition -- from ultra-mafic basalts to granitoids -- rivals that found on the Earth" (although high-silica rocks are rare). They also note the vast variety of strange markings beneath the seasonal CO2 ice cap, "consistent with a translucent, impermeable CO2 ice cap that sublimates from the base, producing gas flow beneath the ice that erodes the channels and jets that erupt sand-sized grains through vents. These processes are unlike any observed on Earth. The vertical stirring of the polar-layered deposits by this process may have significantly altered the sedimentary record, and may complicate the interpretation of the sedimentary record as it relates to climate history."

The vents are very interesting...could there be a similar process in comets? Could 'base' subliming CO2 or H20 open jets that expel water vapor? Why is the CO2 subliming 'from the base' rather than from the top down? Does Mars have moles