Top: Meridiani Planum, as seen by the Opportunity rover, in foreground. In the background is the rim of Endurance Crater, 8 km away. Bottom: The fine layering and cross-bedding of the sediments can only be seen inside craters. This image was taken inside Endurance Crater. Both images are photo-mosaics, courtesy NASA/JPL Photojournal.
A preliminary study was conducted in order to investigate the rate of acid-weathering at very low temperatures. In this study, forsteritic olivine, was exposed to sulfuric acid in capped test tubes under different temperature conditions (-52°, -20°, 4°, and 20 °C) for varying amounts of time. For the sub-zero temperatures, the acid concentration and the temperature condition for a particular sample were chosen so that the solution and ice would be stable together. Atomic absorption spectroscopy (AAS) was used to analyze the solutions for their concentrations of dissolved Mg2+ and Fe2+ ions from the dissolution of the olivine. The solid residue was examined for evidence of weathering with a scanning electron microscope (SEM) using backscatter electron (BSE) imaging and energy dispersive spectroscopy (EDS), which gives qualitative chemical analyses.
BSE images of two olivine grains. A. is a residue grain from the longest duration -20 °C sample. B. is from the least weathered sample (-52 °C, 1 hour). EDS are also shown, showing differing Mg:Si between the two samples.
The results of the analyses suggest that acid-weathering occurred in even the coldest temperatures and rates and magnitudes comparable to those at higher temperatures. Both Mg2+ and Fe2+ were found in all the solutions, with the samples in the coldest conditions having the lowest concentrations. Additionally, the concentration of the acid seemed to compensate for the colder temperatures in the first 24 to 40 hours. However, when the rates of the reactions were calculated, the rate drops off very quickly in the coldest temperatures (where initially it was relatively close to the warmer reaction rates), indicating that the temperature does play a large role in slowing the reaction kinetics of olivine weathering. We hypothesized that this temperature effect may be due to slow ion diffusion around grains in the coldest temperatures. Furthermore, the BSE images and EDS of the solid residue give compositional and textural evidence of sub-zero temperature acid-weathering. The ratio of Mg to Si is much lower than typical forsterite composition in darker colored areas and spots (color differences indicate compositional differences in BSE images), showing that some degree of weathering has occurred, possibly in conjunction with the genesis of a weathering product.
Additional information about this study can study can be found here: http://www.lpi.usra.edu/meetings/lpsc2010/pdf/2599.pdf
This post provides a really great description of the research and study overall. However, it may be a bit overwhelming for a general audience because of the jargon and detail. It may be helpful to discuss the purpose and results of the study more generally, and explain their relevance to our understanding of Mars. Without a geochemical background, it may not be clear what the implications of the study are.
ReplyDeleteAn interesting read on an interesting topic. You do a good job making a connection for the reader initially, and the photos serve to enhance this (who isn't interested in photos of another planet's surface?).
ReplyDeleteHowever, a lot of the language feels inaccessible to someone without a background in Geology. You may want to consider defining certain terms or changing them to more common ones ( for example: playa, aeolian, the analytical techniques used).
Overall, a very interesting post describing some interesting experiments. I just have a couple of questions: Out of curiosity, how were you able to maintain any liquid at those subzero temperatures (especially -52degC)? I would expect a frozen, inert solution (apparently not though!). (Are the olivine grains weathering in ice??) Also, I was a bit confused about the hypotheses you outlined in the beginning (groundwater-fed evaporative playa, acid weathered dust/ice deposits reworked by wind). Are these competing hypotheses for the formation of this region, or is the second some kind of modification to the first? I just didn't understand their relation (if any) very well from the text, perhaps some clarification is needed.
ReplyDeleteThis is really interesting work and I like the fist set of pictures. However, you may want to consider re-ordering the first few sentences. It might draw in your reader a bit more if you start out with the water on Mars statement and a brief description of the evidence but then say that this same evidence can also be explained through acid-weathering. (Basically, get rid of the first sentence and combine the 2nd and 3rd sentences.)
ReplyDeleteInteresting, substantial, and attention-getting, but, at least in my opinion, ultimately difficult for a general audience. Breaking terminology down a step further would allow a wider readership to enjoy the contents.
ReplyDeleteA comprehensive post about a very interesting study. Although the title reflects the topic of the article, it could be a bit more catchy like the pictures of the Martian surface, which are really striking. Also in the text are a number of technical terms (hematite, forsterite, aeolian processes, ion diffusion, SEM/BSE/EDS) the general audience will not understand without further explanation. Nevertheless, the text is well structured and gives much information about current research on Mars.
ReplyDeleteAn interesting experiments, though I do not follow why people do this research.put in another way, what's the movitivation is not clear to me.
ReplyDeleteFor the BSE and other analysis, it'd better provide the composition of olivine before the experiments.
This post was interesting and an easy read. You may want to try to make the reading more accessible (the formula for olivine would be good for a general reader). Also, do you have the drawn illustration about what you think is going on with the olivine weathering that was on your LPSC poster? I think that would have been a good addition.
ReplyDeleteI am (as I mentioned in class) a little torn by the last figure. On one hand, it's great to have your two best pictures, and to be able to see the difference. On the other hand, I think it's too easy to miss that these pictures aren't meant to be directly comparable.
ReplyDeleteOverall, though, a neat topic and a nice presentation. It had never occurred to me that acid concentration via freezing might be helpful for understanding Mars weathering. It would be nice to see a little more about the implications of whether cold weathering is important.
This seems like a really interesting study, but I think I would like to see a stronger take-home message at the end and maybe how it has changed our impression of environments on Mars. Also, the blog seems pretty technical, many people might not know what olivine even is. Pictures and captions seem good.
ReplyDelete