Titan Crater Topography Through Stereo

To give a little background, I updated the crater population on Titan by identifying all the craters at the end of Cassini. Then I characterized their morphometry using limited topography in SARTopo, which give thin lines of low resolution topography where overlapping images were taken within a single swath. With this, I define certain parameters to study how the crater was changing. Crater size (diameter) is crucial because the shape of the crater is often presented as a function of diameter. The depth is also important because it gives quantitative constrains on how degraded a crater is from its original (deeper) depths. I took it a step further and measured rim heights as well.

However, the reason I have had to continue studying this is because I have been comparing SARTopo to standard stereo topography. Stereo is similar in that it is acquired where we have entire RADAR swaths overlapping. This provides a 3D look at the crater rather than a single (may 2 or 3) profile through the crater. Furthermore, SARTopo is at ~10km per pixel resolution. Stereo is more like ~2km per pixel. This is relevant because we measured “freshness” of a Titan compared to Ganymede craters. Ganymede is ~same size and density as Titan, so it is expected tat its craters will form in similar manners. The problem is that the topography on Ganymede is ~1.5km per pixel. This is significantly less than Titan, and it becomes a problem when measuring sharp peaks (i.e. low wavelength topography) because lower resolution averages these peaks with surrounding lower topography giving artificially lower rim heights. However, you see that Titan stereo resolution is more on par with Ganymede topography, so we can use it as a test case to see 1) how it compares to SARTopo and 2) if degradation still remains.

Unfortunately, we have come across yet another problem. The Titan stereo results (presented in various Neish et al. papers) was measured using a method that takes statistics of the entire rim and floor values rather than a single profile. I would argue that this is probably the most representative measurement of the crater parameters. However, our comparison is with Ganymede using previously published results from Bray et al. (2012). Brey et al. (2012) averages up to 8 profiles through Ganymede craters; we need Titan stereo measurements that mirror the Bray et al. (2012) methods for it to be comparable.

So, without getting to into the details, I found the 6 craters with stereo (Ksa, Soi, Santorini Facula, Shikoku, Forseti, and Hano). I uploaded the DEM png’s into matlab and manually assigned lat and long values (that was annoying). That may not have been necessary, but I wanted to be able to go back and see where the data was taken. Then I decided to take 8 precise profiles from the crater. I did this by creating a vector (list) of angles from the y-axis then found the right x and y values for each profile. This took a lot of troubleshooting, and I am fairly impressed with my ability to get this done one step at a time. It was particularly difficult where we had partial coverage. I almost just went with the two best craters we had and let it be, but I really wanted to include all the data we had.

The first thing to notice is that not all craters have full coverage, so results are limited to where we do have coverage. I tried to extend up to 5r out (as with Bray et al) where possible. However, I never ended up needing the extra topography because I didn’t go so far as to back out topography. Each black x represents the rim point I found. Then a show 3 of the best examples we have data for with the 8 profiles for Ksa, Soi, and Shikoku where you can see how these values where found. The rims and floor positions are marked with blue marks; the red marks are from previous literature for reference.

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The Final Result

What I have done is re-purposed my previous plot of rim to floor depths (the traditional depth measurement) to include H18 stereo measurements. Ganymede craters are in black. Titan craters are color coded for the 6 stereo craters to compare Neish stereo, H18 stereo, and SARTopo. SARTopo is shown in red if there is no stereo to compare to. What we notice is that there is a 3:2 ratio of craters that have SARTopo depths larger than stereo. Forseti (blue) is lower than SARTopo, well outside the margin out error, but ~same as Neish measurements. Hano (light blue) is lower than SARTopo but more on par than the ~0km depth from Neish et al. Soi (orange) and Ksa (cyan), the ones with the best coverage, show SARTopo slightly below stereo but well within the margin of error for each. While Shikoku (yellow) is below SARTopo, well outside the margin out error. H18 stereo is about the same as Neish et al. for Santorini (green) but slightly above.

 

depth-and-stereo21.png
Rim to floor depths of Titan (circle, triangle, square) and Ganymede Craters (diamond, line). SARTopo is in circles. Neish stereo in squares. H18 stereo in triangles. The 6 craters in stereo are color coded in both stereo and SARTopo (if available). SARTopo without stereo is shown in red.

 

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Starting Off Right: My Trip to Dragon Con and Work Ahead

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So, I spent the weekend visiting friends at Dragon Con in Atlanta. It was a blast, and this year I made sure to get at least 5 hours of sleep each night. Unfortunately, that meant I kept missing early panels I wanted to go see. I ended up spending most of my time playing games with my friends that I don’t see very often. Although, I did manage to attend two panels. One was hosted by Cecil Baldwin, of the Welcome to Nightvale Podcast. It was on queer representation in Horror films. There are a few new horror films I want to watch now, and even more that I want to rewatch with a new point of view. The other panel was on the mature themes in a Handmaids Tale. I still haven’t finished season 2, but I still enjoyed it. The panel asked some interesting questions like what constitutes rape in this world. Even consensual sex between June and Nick is arguable a form of rape because that wouldn’t be happening if she wasn’t in this position. It essentially her best attempt to assert some control over her own life. Then there was a question over the justification for violence, and if it is justified, then when is that threshold where it becomes okay?
All in all, I regret not seeing more. I didn’t make it to a single Space, Science, or Skeptic panel. To be clear, I wanted to, but in the moment, it is easy to get invested in gaming for hours on end. Then its a question of navigating from Hotel A to Hotel B which makes some panels more difficult than others. There is just simply too much to see and do.

The gaming was mostly Ultimate Werewolf. Although as a group, we tend to play all sorts of deception games including secret Hitler, Two Rooms and Boom, etc. It is a great way to have fun and get to know new people.

The trip wasn’t perfect. It’s long and stressful (but I don’t regret it). Still, my car stopped working on my way home and I had to spend the day in Michigan at a mechanic. It was over 90F (32C) and it was terrible. Luckily, they got it going, but I think it may be time for me to begin making arrangements to say goodbye.

Now, lets get to business. My current agenda has me finishing the Titan Craters paper by updating the Stereo results. That is my number one priority at the moment. From there, I need to move on to my new project(s). With that in mind, I have a few ideas to discuss further with Catherine. We’ve already spoken about studying how molecules will freeze in an impact melt pond. I’m also interested in testing the stability of a melt pond in an impact crater. If we have a porous subsurface, water will drain out, but how fast? The slower it is, the more time the pores have to fill with frozen water. My idea is that we may be able to model at what porosities a pond may remain. A shrinking pond also introduces the possibility (if flimsy) of wet-“cold-dry” cycles. This is a stretch, but McMaster University showed us how they are simulating wet-dry cycles with their planetary simulator to encourage polymerization. It likely will not happen at these cold temperatures, but I am curious how these molecules may act when frozen in a rigid ice matrix. Furthermore, if we consider a pond that is draining yet simultaneously freezing, we might imagine a hanging roof of frozen ice that may break and remix partially. Again, its a stretch, but I spent a week hearing about this wet-dry cycle and tried my best to think how if at all it could happen on Titan. Even if we disregard this cycling, the question of melt pond dynamics in a porous environment is still interesting.  I need to talk to Britney and her group, but I think Jacob, who is working on ice-water interactions in Antarctica and Europa because I think this type of project is still similar.

Other courses of action are, investigating Impact craters in RADAR. I assume that would involve RADAR processing (roughness, CPR, etc.) then mapping and inferring and possible ground truth planning. One other project which we spoke about (but one I am not all that excited about) is mapping fractures to river orientations. That is something I still need to discuss with Oz to get feedback about the report I made.

I also remind you all that I will be gone from October 6th to 14th (I think) for the Meteor crater course. I will also be gone for a cruise during Halloween (very sad about that).

 

The End is Nigh: Updating and Finalizing My Thesis

Having successfully defended my thesis, I am now in the process of making a few revisions. It isn’t anything too extreme; a couple changes and a few additions to the intro is all it is. I’ve looked into getting permission for figures in my intro. It was very easy, and I’ve taken care of it for all of my existing figures. Any new figures I add won’t take any time to get permission for either. For the bulk of this blog, I’m going to present here a few of the “major” additions I’m making (since thats where my focus has been), which is essentially just more background info about Titan/Cassini.

Outgassing of Methane from Titan’s Interior

Justification for section

I chose to expand on this because there were a few questions related to the outgassing event. Dr. Tornabene wanted to understand the connection between outgassing and volcanic events. Dr. Campbell-Brown wanted to know more about the existence of Argon in the atmosphere and why it is an indicator of outgassing. Dr. Molnar wanted to better understand the origin. By delving deeper into the outgassing history, we get a better idea of Titan’s timeline/history and how it likely formed. Then I can discuss how isotopes (Argon and others) support this history while also commenting briefly on what it says about the material that sourced Titan.

This is presented in Chapter 1.2.1 Titan’s Atmosphere and Climate, now labeled Titan’s Atmosphere and Origin.

Excerpt of Original Material 

Titan’s abundance of methane and organic compounds results in a complex cycle of rain, erosion, and deposition. Titan’s surface pressure is very similar to Earth’s (1.5 bars vs 1 bar), and with temperatures at 94K, methane can be stable as both a gas and liquid (Kouvaris and Flasar, 1991).  Titan’s methane isn’t in an ocean like water on Earth, rather it is in large lakes, and the specific heat (the energy needed to raise a substance by 1K) is harder to overcome because of the lower solar flux (Lunine and Atreya, 2008). Nevertheless, rainfall and cloud events have been observed if rarely (Turtle et al., 2011; Porco et al., 2005; Griffith et al., 1998). Modeled rainfall requirements for the observed channels suggest that there should be twice as much methane vapor in the atmosphere than observed at the equator (Lunine and Atreya, 2008). Short term (100s of yrs) rainfall could be fueled by evaporation of the lakes, but methane is slowly being destroyed over a much longer lifespan of 10-100 Ma (Figure 6). Therefore, it has been suggested that outgassing event(s) have released methane from the interior in Titan’s past to resupply its atmospheric methane (Figure 7) (Choukroun et al., 2010; Choukroun and Sotin, 2012; Tobie et al., 2006).

New Material

ch1 fig

Figure 7: A theoretical evolution of Titan’s interior (b) and how it has affected the outgassing of methane throughout Titan’s history (a). The outgassing rate is controlled by the interior evolution (a). The final outgassing event is shown  with 10% and 50% of the methane reservoir outgassed since the second outgassing event. This is modified from Tobie et al. (2006).

Tobie et al. (2006) present a theoretical evolution of Titan’s interior that composes of three major outgassing events. The first event begins with the quick overturn of Titan’s initial core. The outpouring of methane produces a thick layer of methane clathrate above the ocean because of how methane interacts with liquid water under Titan’s temperatures and pressures (Tobie et al., 2006; Sloan 1998). Clathrates are compounds that are trapped within the ice lattice. These can alter the rheological and thermal properties ice as well (Durham et al., 2010). The low viscosity and low conductivity acts as an insulator, warming the ocean which releases methane. After differentiation, the silicate core begins to convect; the heat flux thins the clathrate layer with the buoyant methane accumulating at the base and escaping through cracks (Tobie et al., 2006; Lunine and Stevenson 1987). As the interior cools, the liquid ocean begins to freeze to form a layer of ice I. The thick ice layer convects, forming warm plumes (likely from tidal dissipation, Sotin et al., 2002) that breaks through the clathrate layer making it unstable. Tobie et al. (2006) suggest the last stage occurred perhaps ~1.0 Ga. This model explores a range of parameters but finds that the change in these cycles is the length and intensity. Furthermore, it is consistent with the signs of volcanic features that would form during this event (Elachi et al., 2005) and with isotopic signatures in the atmosphere.

            Isotopic measurements help to verify the outgassing events but also constrains the origin and evolution of Titan’s volatiles as a whole. Evidence  of 40Ar in Titan’s atmosphere reflects the decay of 40K which would have been sourced from rock-water interactions, and its existence in the atmosphere suggest potassium rich water magmas reached the surface through volcanism likely fueled by the outgassing (Wait et al., 2005; Niemann et al., 2005; Tobie et al., 2006). Another line of evidence comes from the lack of enrichment of heavier carbon isotopes in methane despite seeing it in nitrogen isotopes. The 15N/14N ratio is enhanced as heavier 15N sinks below the 14N which can escape more readily (Lunine et al., 1999; Hidayat and Marten, 1998). Inversely, the ratio of 13C/12­­C in hydrocarbons is closer to the terrestrial value suggesting it has not undergone the same escape enrichment. That is to say, the carbon in the hydrocarbons (i.e. methane) have been recently sourced (~1 Ga or less). Congruently, the deuterium in methane is lightly enriched (~1.5 times) which is still significantly lower than organic molecules in organic clouds (i.e. the outer solar system) (Van Dishoeck et al., 1993; Meier et al., 1998). This reflects the slightly warmer circum-Saturnian nebula that would have undergone more processing of the volatiles that likely sourced Titans reservoir (Lunine and Tittemore, 1993).

Crater Morphometry and Scaling Laws

Justification for section

There was a good bit of confusion on the scaling laws that are shown in plots, and this is an important piece of my work. I expand on what is already there to help them understand the relationship between scaling laws and the worlds being studied. This is not as extensive and is more integrated with what was already there.

Excerpt of Original Material

The most descriptive characteristic of a crater is its diameter. The diameter of a crater can be used to predict the approximate depth and overall shape of a crater. The material properties of the planetary body also matter (see above), but the transition point from simple to complex to multiringed craters is unique for each body (Bray et al., 2008; Schenk, 2002, 1989). However, some planets are sufficiently similar to compare. Gravity is the driving factor behind the simple-complex transition diameter, but lithospheric structures also influence this transition because they can be indicative of the thermal structure in the crust (Melosh, 1989; Schenk, 2002; Turtle and Pierazzo, 2001). The thermal structure controls how material will react to the force of a shock wave; warmer material tends to act more ductile (plastically deforming) than brittle (faulting) (Turcotte and Schubert, 2014). This is especially important on icy moons where temperature is the driving factor in viscous relaxation because it controls the viscosity of the material (Durham et al., 2010; Schurmeier and Dombard, 2018).

New Material Mixed with more Original Material

Therefore, it is important to accurately characterize the diameter of a crater to accurately constrain the global trend of crater morphologies (Figure 12). These trends are known as scaling laws; this approach is often used for terrestrial worlds. Schenk (2002) discusses how it changes for the icy moons of Jupiter. Compared to the moon, the simplest craters follow the same trend, but the transition to complex craters occurs much sooner because of the differences in material strength and body gravity. For similar reasons, these icy moons reach a point where the complex craters (with central peaks) become central pits. The effect of size and strength is observed best with Europa because it is being embedded with significant tidal heating. Therefore, the transitions occur sooner, but worlds of similar size, thermal structure, and material strength often have very similar scaling laws (e.g. Ganymede and Callisto).

scaling law

Figure 12: Depth/diameter measurements for fresh impact craters on Ganymede. The thick lines are for lunar craters, and the thin lines are least-squares fits through the Ganymede data. Simple craters are solid dots, and complex craters are split into those with central peaks (open circles) and central pits and domes (crosses). The multiringed craters are shown with error bars.

Titan, like Earth, undergoes a great deal of degradation (see Section 1.2 and 1.3.5), so the crater structure becomes harder to interpret. Turtle et al. (2005) addresses the issue of crater diameters identifying the difference between the final rim diameter (rim to rim distance after forming) and the apparent crater diameter (rim to rim distance after erosion). Terrestrial (and Titan) craters undergo significant degradation which make it difficult to find the crater rim even with topography (Figure 13). Without a population of fresh craters, you are not able to develop a unique scaling law. Multiringed basins are similarly difficult to characterize even before erosion. In these cases, the best approach is to clearly identify the ambiguity required when interpreting a crater. An example of this is like Schenk (2002) showing multiringed basins with error but not a trend line if to it.

(Image of degraded craters).

Other work needed

There is a brief addition to chapter two I need to add related to data processing so it is clearer what I did in my thesis. Although, the bulf of the work is just making these changes to the intro. There are couple more “major” changes I’m still working on, 1) cratering rates (a new subsection to discuss in more detail) and 2) Discuss the degradation of titans craters from a material perspective. Elaborate on whats souring the fluid/infill. Mention Alyssa’s work and Catherine’s 2015 work.

I’m posting this now, but I’m hoping to add at least one more section before I present this at group meeting 8/15/18 1PM. For now, enjoy.

 

Preparing for my defense

I’ve been working on preparing my thesis presentation for the world to see, and by world, I mean maybe 10 people. I’ll present it live on facebook or youtube too probably.

My thesis is Friday August 3rd at 1PM.

In other news, I have an updated manuscript that is mostly ready to share with the Cassini team. However, there is one more thing I need to do.dr plot

I used this figure to show that SARTopo data is on par with Stereo data. SARTopo is ~10km per pixel will stereo is ~2 km per pixel. The worry is SARTopo will artificially lower the highest peaks by averaging the sharpest peaks with lower terrain around it.

Sinlap Depth Figure Arrow

For example, the average terrain height on the left and right of the depth profile above is not a perfect fit, the peaks are not seen there because they are averaged over a large span of heights including lower heights. However, if stereo doesn’t do that averaging and gives the same result as SARTopo, then we say it probably isn’t a big problem in SARTopo. The problem is, past stereo measurements of stereo data did a 2D averaging of measurements with the stereo. The method we are using with SARTopo is done along the lines of Bray et al. (2012) were they take, I think, 8 profiles and do what we did, measuring the values for each profile then averaging it. If we are going to use stereo as a proof that SARTopo is reliable for measuring sharp terrain changes, then we need to make sure the results were acquired using the same methodology. Unfortunately, that leaves me with the responsibility of having to do the measurements with the stereo data. The only reason I had not done that already was because my study was using updated, and possibly changed, data sets. Stereo data has not changed since these measurements were done, so I thought this wouldn’t be necessary.

Ithaca, Orlando, Jacksonville, Vancouver, and Atlanta: Oh, the places I’ve gone.

“You have brains in your head. You have feet in your shoes. You can steer yourself any direction you choose. You’re on your own. And you know what you know. And YOU are the one who’ll decide where to go…”

Ongoing work (before Recap):

Working to finish current draft of thesis while finalizing results. One thing I still cannot to get to work is the Anderson Darling test. It is supposed to test whether two data sets are independent distributions, but MATLAB only lets me test if a single data set fits a predefined distribution (e.g. normal, exponential, lognormal, etc.). So I don’t know how I am supposed to compare the two. I tried doing this before and could not get it to work then or now.

I just discovered a Two-sample Kolmogorov-Smirnov test on MATLAB. From what I can see KS and AD are often used interchangeably. I think I am going to go with this for now. That said, my confidence in this is minimal. I ran the code on Titan depths and Ganymede and it rejected the hypothesis that they are from the same distribution. I repeated this using the Ganymede depths and the trend-line Bray et al (2012) defines and it also rejected that.

I thought, maybe the different sizes is effecting the result. I tried it where each data set was in an equally sized distribution with the same sorting, but the result was the same. Bray data points don’t follow the trend line defined by Bray, nor does Titan follow the Bray data points (supposedly). More work is clearly needed.

Recap:

When was the last meeting? I think it was before my May trip to Cornell in Ithaca, NY. That was a lot of fun and very educational (see featured image). There’s plenty to talk about, but I’m going to show you the new stuff I presented (and am continuing to edit).

Titan Workshop

Figure 1 shows the adjusted impact crater population on Titan. I found the probability of detecting a crater of a certain size then calculated what the actual number probably is. I compare my results with Neish and Lorenz (2012), and they align very well (with fewer small, <10km, craters).

Figure 6 Crater Count2 (1)
Figure 1: The number of craters on Titan, adjusted for limited coverage.
Sinlap Depth Figure Arrow
Figure 2: Sinlap crater mapped showing the rim depths (blue) and the terrain based depths (black).

 

Crater Topography.jpg
Figure 3: Rim heights (top), rim depths (middle), and terrain depths (bottom). These results need to be updated because I need to go through and back out the local topography

I am still trying to figure out backing out the local topography slope, and that may change the results. The point is to try an figure out if the lower resolution in SARTopo (Titan topography) is lowering the measured rim heights compared to Ganymede’s higher res topography. While it’s too hard to differentiate the terrain heights on Titan and Ganymede, note the SARTopo (red) and stereo (blue) match up fairly well, and stereo resolution is more on par with that of Ganymede. Suggesting, resolution is not a problem.

Family

Between then and my next meeting, visited my mom and then my dad during the second to last week of May. Then I returned to my dad’s the first weekend of June for his wedding which was delightful.

TEPS

Right after that (you might even saying during), I got to fly to Vancouver for the TEPS 2018 Summer Workshop. This was another enjoyable trip. I’m not sure why, but I think I enjoyed it more this year than last year. Maybe it was because I knew what to expect.  What I enjoyed most was the talk by Dr. Rory Barnes about habitability and exoplanets. I was really intrigued by the discussion about the formation and habitability of the Trappist-1 system. Another thing he spoke about was their new online public habitability program they are about to (/have?) released. It seemed like a really interesting approach that tried to help students visualize how all the different parts of a solar system influence the habitability in a way that others haven’t. I’m interested in playing around with it to hopefully develop/update an existing lab for Western’s Astrobiology course. I’ll look at that more later when I have time.

AbGradCon

This was another great meeting. I really enjoyed getting to experience a conference that was entirely grad students. Although, I wouldn’t mind some background talks to introduce things (considering its a broad field). Nevertheless, there was a lot of good talks and posters, and I felt like my previous meetings have helped prepare me for the conference.

I presented my research and did some advertisement for Dragonfly (which I will do again next week in presentation form).

After thinking about Titan and the goals of dragon fly so much, I got an idea I’m really excited about this idea, and I’d like the opportunity to flesh it out more when I have time (in the fall). But I’ve done a quick review that I’ll basically state here for initial feedback.

New idea: The dissolution of organics and refreezing of melt in impact craters on Titan.

Essentially, I want to study the process of refreezing after impact to assess what we would expect to see, and where. Dr. Britney Schmidt’s (GA TECH) PhD student, Jacob Buffalo has developed a MATLAB code with Dr. Chris Huber (Brown) to study how arctic sea ice refreezes and the effect on salinity in the ice and the water. He uses the arctic ice as a means of testing the validity of his model so that he can use it for predictions on Europa. I have seen this discussed before, but it was with Dragonfly on my mind that I was able to see the application to Titan.  I’ve spoken to Jacob and Britney about it and they both think its a great idea and that their model could easily be translated to Titan.

I’m interested in applying this model to Titan for multiple reasons. While impact craters are capable of maintaining melt for 100s to 1000s of years (Davies et al., 2010; Neish et al., 2008), how long will it remain liquid near surface. Realistically, Dragonfly will be restricted to the surface or to the melt exposed/transported by fluvial erosion. My interest is to investigate how impact crater on Titan will refreeze. However, I’m also interested in investigating how organics (and potential bio molecules would 1) effect refreezing and 2) be distributed in the ice/liquid environment as it refreezes.

The long term goals is to provide potential investigations (i.e. Dragonfly) with information on where to best search within a crater and to manage expectations on what we should expect to find near surface.

This project would use existing knowledge of organics on Titan (e.g. Lorenz et al., 2008) and the types of molecules they form in water (Neish et al., 2008) to translate existing models to Titan, and it would create opportunities to collaborate with others for modeling (J. Buffalo and possibly Zibi or Ralph larger scale look).

Up to this point, I have expressed interest in Astrobiology, but my research has not been directly related. This is an opportunity to introduce myself to the field of astrobiology by incorporating multiple areas of science in a way that will strengthen my expertise in each.

Lost in Spaces: Updates on Writing

There isn’t a lot to report. I’m in the processes of writing (my first draft of manuscript thesis chapter). There was a little shuffling since our last meeting because I reworked the outline of my manuscript.

  • Introduction (last week/done)
  • Methods (this week/in progress)
  • Results (next week/results in progress)
  • Conclusions (First week of May)

That puts me about a week behind when I had reported to finish last time. That said, I was leaving a week to prepare for Titan meeting so there was wiggle room. I’m on track now, but I do fear a slight lag of ~1/2 week.

For next week, there a couple results I’m still working on.  The first is more tedious than anything. We have 30 new craters that’ll look pretty much like Figure (1). It’ll look like this, but I’ll be making some changes. First, I’ll move the figure from word to Photoshop (to maximize image quality). Then there will be some shifting of the crater images and the labels within it. I’m thinking names/labels in top left of each square with certainty at the top right. Before that, I’ll reorder them to be from largest to smallest (in diameter). Right now, they are biggest to smallest, but they are separated into my and Catherine’s crater findings. This will probably take a few hours but hopefully not more than that.

craters
Figure 1: 30 New craters found on Titan. Certainty from 1 to 4 (1 being certain 4 being possible). Image is being edited and improved.

After that, the next biggest change I need to complete is to measure the depths of craters relative to the average depths of the local topography (Figure 2). There are two ways of doing this, (1) arbitrarily assigning some height by eyeballing it, or (2) take an average on either side of the crater. I’ll be doing the 2nd unless otherwise told otherwise.
This won’t be too difficult. I’ve already got the main code done. What I need to do is make some tweaks. First, I need to change the part of data I pull to extend further outside the crater. You can see in Figure 2 that the topography doesn’t extend to the same width of the RADAR image we use to visualize the crater (~3x that of crater D). I’m thinking using somewhere between 100km and 200km on either side. Hopefully, we have enough data and that does a good job averaging. It’ll be easier to define a set difference than assigning a length (which may be needed due to possible anomalies in local topography). If it is that simple, then it won’t be hard to process all 15 craters again (Figure 3) because the hardest part is assigning boundaries (which are hard to find in the more obscure craters) to search for the rim which I have saved (in an excel doc) for the craters I’ve already done. That also defines the crater floor, so all necessary steps will be done.

depths.PNG
Figure (2): The topography profile that goes through the center of Selk crater (80km), plotted along the same longitudinal axis as the RADAR image. The depth (d) is measured (blue dashed line) by measuring the distance from the upper most rim position and the lowest floor position (black circle) on the left and right of the crater, then averaged. The depth is again measured (dL) by subtracting from a localized average topography on either side (green dotted line).

 

I’ll be updating the comparative plot between Ganymede and Titan (Figure 3) with stereo data and using the local topography to find the depths. The plot is easy, the hardest (but still easy) part will be finding the depths from the local topography of Ganymede, but that just uses the rim heights so it shouldn’t be too bad.

titandepths3.19
Figure 3: The depths of Ganymede’s craters as measured by Bray et al. (2012) (black diamonds) and Schenk (2002) (black dashed line). Compared to Titan’s craters using SARTopo data (red circles), and eventually stereo data (blue x’s). Then I’ll plot the depths measured from the rim height and depths measured from the local topography in separate plots.

Continue reading Lost in Spaces: Updates on Writing

LPSC and a Race to the Finish

LPSC was an amazing experience. The best part was probably being able to experience to interact with people I know (see the cover photo of Kevin, Gavin, Jeff, and me). And, I say that as more than a matter of just socializing (although it was great getting to catch up with Kevin!). Going to this and running into people I know really affected how I perceived my own sense of belonging to the community in a way that changed the entire experience for me. Other than that, I had an oral presentation and I think it went rather well. My favorite session was probably the Pluto session. My first LPSC was brand new Pluto data, and it’s fascinating how much things have changed over the last two years. Of course, I really enjoyed the Titan and Cassini sessions. Although, I was really caught up in my own presentation during those sessions. I haven’t sat down and reviewed my notes, but I should review my thoughts on the things I saw.

With the recent acceptance into Western’s PhD program (yay), there is more pressure to finish writing my master thesis for my defense at the end of the summer to ensure I make it into the PhD program in September. With that in mind, I think an itinerary for the summer is in order.

First up is the month of April.

My focus this month is on the first draft of my manuscript for my thesis and paper. The current outline/plan is as follows:

  • Intro stuff (April 6th) (although I’m not sure if this is necessary if I have a ch1 intro already)
    • Discuss Cassini Data and Titan data and Titan overview (as it relates to impact craters) and a Crater Population overview
    • This is to be done by the end of this week (April 6th). I think the Crater Population overview is the main focus for the week.
  • Crater Population (April 13th)
    • Discuss new craters, the radar imagery and then present a complete tabular data review
    • Discuss the distribution (quantifying spatially) and present updated calculations on surface ages
    • Meet with Catherine, discuss final list and review SARTopo depth data
  • Morphology (April 19th)
    • This involves finalizing sartopo data set (ensuring right rim positions and determine whether all craters used should be used)
    • Gather data for stereo and altimetry (from past sources)
      • compare in depth and diameter and in discussion
    • Each week is planned for Monday-Tuesday writing with Wednesday-Friday free to finalize this topo data and do an analysis of resolution limitations. And that also gives ample time during the rest of the week to catch up if I don’t finish during the first two days of each week.
  • Global Degradation (April 23rd)
    • Depth to Diameter plot and discussion on implications for Titan’s surface
      • easy plot to update with previous week data completed
  • Future Work and Conclusions (April 23rd)
    • Chapter 3?
  • With room to review over weekend and beginning of following week before sending to Catherine for edits.

My May schedule begins to be more hectic and will become more defined as I get a better idea of what my final chapter will be.

My idea of chapter 3 is as follows:

  • Opportunity for future work
    • high-resolution ISS map
    • Dragonfly
    • Landscape evolution modelling
  • Conclusions
    • Summary of crater distribution, morphologies, and the state of Titan’s surface

Really, this is maybe 4 pages of double-spaced work, maybe 5? I don’t really understand how this constitutes a chapter unto itself or how I make it independent.

That said, my May schedule and plan is as follows:

  • May 1-8 prepare updated/final presentation for Titan Surface Meeting*
    • This will be the starting template for master defense presentation
  • Write review opportunities with ISS map and Dragonfly (May 15th)
  • Make any other edits to chapter 1 and crater population of manuscript/ ch2 (May 18th)
  •  Visit Mother May 21-24
    • unlikely to have time to write/edit
  • Visit Dad starting May 25th*
    • Landscape evolution and conclusion (May 28th)
    • Edits to Morphology (May 29th-May 30th)
    • Edits to Global Degradation (May 30th-31st)

Okay, with that outlined, I’ll elaborate on the starred/bolded points. First off, the Titan Surface Meeting is May 9-11. I received notice that I will get my housing and travel covered. I was planning on driving, and I’ll probably be given a room with a local grad student (because I was the only male to receive the travel award and they would have to buy a room for just me). I expect the presentation to be mostly like LPSC with more finalized tabular results, and a depth/diameter plot that compares different topographies with my final take away points listed. This will allow for final comments, suggestions and points for me as I approach my defense.

I’m visiting my mom in mid to late May and do not expect to be free to work those four days. Then I will be visiting my dad right after. I did not initially intend to stay so long. I had to cordinate with my mom, and the timing just made more senses to stay until AbGradCon rather than travel back to london then back to Atlanta (my dad is in Jacksonville). Then I got this huge last second news that my dad is getting married on June 2nd. The timing does work out. My current schedule leaves me with just the final summary of the chapter 3 (may require more work prior to trip if I have underestimated Chapter 3) and edits during the trip. I feel like this schedule is managable, but it is my goal to get the hardest part done BEFORE my trip. Comments and suggestions are welcomed.

For the AbGradCon, I have recieved notice that I will have a poster (impact craters on Titan which I’ll tie to dragonfly and Catherine’s paper in review). I am also getting registration and lodging covered.

I said I could cover flight (and possibly lodging with friends) but they gave me what I hoped for, which was a a comfortable conference expereince. I have registered and made the request for my room (with roommate). The poster, I would rather work on while traveling. I have friends at Tech who can help me get it printed for ~$15 or less on campus. That’s just a lower priority, and I’d like to be able to put that second to revisions and writing.

With that, June becomes a little less hectic than May:

  • AbGradCon June 4th-8th (return morning of the 9th)
  • Ch 1 Edits (if needed) (June 11th)
  • Reedits Ch 2 (June 15th)
  • Edits Ch 3 (June 20th)
  • Science of Early Life (McMaster University) June 24th-June 27th
    • using same poster as AbGradCon
  • Final read through (June 28-29th)

Then July becomes Thesis defense prep

  • Make Presentation July 2-6
  • Edit/Practice Presentation (July 9-13th)
  • Do what July 16-27th?
  • Defend July 30th, 31st?

I know there is more to my defense than presenting it to the public. I need to be prepared to defend it to the committee. Topics to review (to what level?) last couple weeks:

  1. Impact Cratering (9th-11th)
    1. Impact Crater Mapping
    2. Formation Mechanics
    3. Modification (relaxation and erosion)
      1. Landscape Evolution
        1. aeolian (dune processes)
        2. fluvial (rain, river, lake processes)
  2. Icy Moon Structure (Titan vs others) (12th-13th)
    1. tools for defining
    2. implications on impact cratering
    3. differences and comparing
  3. Titan Ionosphere and Atmosphere (and how they interact on a physical level) (16th-18th)
    1. Chemistry review (tholin production…chemical processes)
      1. understanding of early earth atmosphere
    2. Interaction with methane, water, and atmosphere
    3. Implications for life?
  4. Cassini (19th-20th)
    1. Mission life
    2. Instruments
      1. Detailed understanding of radar and making of sartopo (I think I’m still lacking this)

One last thing (summer outreach)

I’m not planning on participating in Fake Space Camp, but I would like to do outreach this summer. Last year I presented twice to the Cronyn Observatory public nights (on Saturdays May-August), and I really enjoyed it. I would like to do that again this year. I have several presentation ideas lined up that will take a little prep work, but will be a fun easy discussion with the public about icy moons, Saturn, Cassini, and astrobiology (i.e. my interests).

I’ve actually got more than ideas, I’ve got an out line for 6 different (sometimes lightly overlapping) presentations. Heres a list of ideas and outlines just because I happened to already have thought about it.

  • A voyage through the solar system (and our place in the solar system)
    1. The sun
    2. Mercury
    3. Venus
    4. Earth and the moon
    5. Mars and its moons
    6. Jupiter
    7. Jupiters moons (galilean)
    8. Saturn
    9. Saturns rings and moons
    10. Uranus and its moons
    11. Neptune and its moons
    12. Pluto nad Charon
    13. Keiper Belt and the Orrt Cloud

This is similar to existing presentations, I would restructure it a bit to make it my own or just use an old one.

  • Life in the solar system
  1. What is life? (and stuff for life)
  2. Life on Earth
  3. Life on Mars
    1. Viking Lander
  4. Europa
  5. Titan
  6. Search for life in the Universe
  7. Kepler mission
  8. SETI
  9. Contact plug

This is a ppt I have from last year.

  • Remembering Cassini (a year later)
  1. History
  2. Launch
  3. Arrival
    1. probe to titan
  4. Life span
    1. Studying Saturn
    2. Visiting Titan and Enceladus
    3. Other Moons and the Rings
  5. End of Mission
    1. Playing iconic end of mission clip from youtube (bring speaker)
  6. Inspirations for future missions
    1. Titan
    2. Enceladus

A new presentation to talk about Cassini and its ending

  • Titan: the most unique moon in the solar system
  1. Location (Saturnian system)
  2. Cassini
  3. previous expectations
  4. Huygens probe findings
  5. Atmosphere
  6. Structure compared to other icy moons
  7. Surface (and processes)
  8. Chemistry and Life
  9. Dragonfly (proposed lander/quadcopter)

Talking about Titan

  • Europa: finding life on an ocean world
  1. Icy moons (an explanation)
  2. Galilean satellites
  3. Tidal forces and liquid ocean
  4. Similarities to Enceladus
  5. Ingredients for life
  6. Europa flyby
  7. Europa Lander
  8. Tests for life
  9. Reality check (on finding life and a Europa Lander)

Talking about Europa

  • Telescopes and satellites: how astronomers study the universe
  1. History lesson
    1. prior to Galileo and Galileo
    2. Galileo to now
  2. Modern Telescopes (amateur astronomy)
  3. Ground Based Telescopes (examples. abilities and limitations)
  4. Space Telescopes (examples, abilities and limitations)
  5. Types of light
    1. explaining what it we are detecting
  6. Rovers, Satellites, and probes
    1. Rovers
    2. Satellites and probes (with examples)
    3. Notable missions
      1. Voyager
      2. Galileo
      3. Cassini
      4. New Horizons, Juno and more

Inspired, I think, by the chapter in the Encyclopedia of the Solar System.

  • Icy moons and Ocean Worlds
  1. Earth
  2. Mars
  3. Icy moons
  4. Ceres and Vesta
  5. Europa
  6. Enceladus
  7. Titan
  8. ??

[see last year ppt; would overlap with titan and europa talks]