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.


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.


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.


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.


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.


Published by

Josh Hedgepeth

PhD student in Geophysics with CPSX at Western University in Ontario, Canada.

2 thoughts on “Ithaca, Orlando, Jacksonville, Vancouver, and Atlanta: Oh, the places I’ve gone.”

  1. Hmm, we’ll have to think about this idea a little more. Please read O’Brien et al. (2005) and Neish et al. (2006) in the meantime. In broad strokes, organics will probably concentrate in the middle of the melt sheet. Unfortunately, we don’t really know how thick these melt sheets are on Titan, as some melt may drain away through fractures (Elder et al., 2012). We also don’t really know what the concentration of organics are. I’m curious to learn more about this sea ice model – perhaps we can use it to investigate the parameter space in a broad way.


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