A quick re-introduction to myself

Hi everyone! It’s been a minute…but you could blame the Canadian summer for that haha! It’s lovely BUT short, so I was busy exploring and taking advantage of this great weather. 😀 And so, after practically being MIA for most of the summer, I thought it’d be a good opportunity to re-introduce myself here on my blog.

I’m not entirely sure if I broke the news here or not, but I successfully upgraded to a PhD program at the start of this summer and am quite excited about the next part of my grad life 😀 It still feels unreal that starting this September, I’m officially a 3rd-year PhD student…like what!? For those of you who do not know/remember, I came to Western University from India in February 2021 and enrolled as a master’s student even though the original plan has always been to start my PhD here. Finally, in May 2022 I was able to get on the PhD train lol and for the most part, it’s been a smooth ride!

As some of you might remember, my first project (ooh it feels great to say that! :D) is mainly focused on the radar-dark halo craters (RDHCs) on the Moon. These are quite unique and are surrounded by distinct, ring-shaped (almost like a halo) structures with unusually low radar-return (hence the name). In my work, I use various radar (Earth-based and orbital) and microwave data to conduct a multi-wavelength analysis of the physical properties and the mechanism of these haloes. Some of these datasets include Arecibo (P- and S-band) and Mini-RF (S-band) radar data, Microwave Radiometer (MRM) brightness temperatures from Chang’E-2, LRO Diviner Rock Abundance data. Additionally, I also compare my observations of these radar-dark halo craters to normal craters to figure out any significant differences between the two.

A quick summary of my work on radar-dark halo craters so far:

  • The halo has low CPR and rock abundance compared to the craters’ continuous ejecta deposits, which indicate decreased surface roughness at the wavelength scale.
  • The passive microwave data (brightness temperature TB) from the MRM shows slightly warmer brightness temperatures for the dark haloes compared to the continuous ejecta. This indicates that the microwave emissions in the halo regions are coming from warm rocks at greater depths.
  • The increased TB is more noticeable in the 37 GHz band than the 3 GHz (which has a deeper penetration range).
  • From my sample pool, older craters like Petavius (age: Late Imbrian, 3.8 Ga) do not show any significant TB differences between the halo and continuous ejecta at all. I would like to look at other older RDHCs to check whether it’s true for all the older craters.
  • Comparing these CPR, RA, and TB values of the RDHCs with normal craters was a bit anticlimactic. The surface roughness and brightness temperature trends for normal craters are about the same as RDHCs, which is both interesting and confusing at the same time.
  • I took a short break from this project over the summer but as I refocus on this over the fall, my plan is to incorporate older RDHCs and a new dataset (H-parameter) in my work.

For my second project, I’m focusing on computing the regolith thickness in the halo regions of these craters. In order to calculate this thickness, I study some very small impact craters surrounding the RDHCs with certain morphologies. The idea and the methodology for this little side project are based on this work by Bart et al., 2011 and this work by Quaide and Oberbeck, 1968. Similar to their work, I’m also looking at LROC NAC images to find these small craters around the RDHCs I’ve worked on. The idea is to look for certain morphologies in craters such as flat bottomed, central mound, concentric nature etc., which are believed to have formed by impacts on a substrate covered with fragmental material (regolith). Such craters usually range in size from about <30m to ~200 m.

For my work, I’ve decided to take samples of such craters from three different areal categories: (1) dark halo region, (2) continuous ejecta (3) surrounding terrain outside the dark halo boundaries. Once I’ve identified these craters, I’ll use the previously derived equation to measure the regolith thickness. The equation correlates the crater morphology to the depth of the regolith in which they formed. The equation is as below,

thickness= (k-Df/Da)Datan(a)/2

Here, k is an empirical constant (0.86) and tan(a) is the angle of repose of the material (~30o), Da is the apparent diameter of the crater and Df is the diameter of the interior feature.

Honestly, finding the craters themselves has been the most time-consuming part of the process, and to make matter worse, I had to redo some of the previous work because of a software crash 😦 Currently, I have calculated the regolith thickness for Copernicus and am in the middle of doing that for Aristoteles. As you can see, I have to zoom in quite a bit to find these craters and it takes some time AND patience haha!

  • So far, I’ve found more such craters in the dark halo region compared to the continuous ejecta
  • The most dominant morphology I see is craters with a flat bottom, followed by concentric craters (which by the way are very hard to recognize as they get smaller in size).
  • So far the craters I’ve identified range in size from about D=11 m to D=181 m but most of them are around 25-40 m diameter. I think I’ll be able to better constrain the size distribution once I have looked at more RDHC sites.
  • Regolith thickness results
    • Continuous ejecta: ~2.85 m
    • Dark Halo: ~5.94 m
    • Surrounding Terrain (SE/SW): ~9.43 m
  • The dark halo has thicker regolith compared to continuous ejecta, which is quite interesting! To me, it does make sense that dark haloes have “more regolith” compared to continuous ejecta, because that would also explain the low CPR and RA for that region (because the material is more unconsolidated/has relatively low cohesion)
  • Plus, I expect that regolith consistency varies even locally. Though, what is the extent of that variation? And how do I tie it with my TB observations? That’s something I have not figured out yet and need to read more literature on that subject.
  • One last thing that I’d like to spend some more time on is the relation between regolith depth and crater densities in the area. Bart et al. noticed that thinner regolith depth correlates with lower crater density, which is similar to what I see for Copernicus as well (lower crater density in continuous ejecta along with thinner regolith depth).

Other than this, I’ve also started writing up my work on the RDHCs and hopefully will have my first draft ready for Catherine by the end of this month! 🙂

Until next time!

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