Ultra-Violet, Ultra-Conference

A false colour image of Mars as imaged by the OSIRIS instrument in 2007. In this image the UV channel has been enhanced, which brings out the atmospheric cloud. Our research program here at PVL often leads us into ultra-violet territory, as Dr. Christina Smith details below!
(Image Credit: ESA & MPS for OSIRIS Team MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA)

by Dr. Christina Smith

Last year I attended the 47th Lunar and Planetary Sciences Conference (LPSC) in Texas for the first time. It was a very different conference to those I had previously attended. It is an enormous conference, around 1700 people attend each year, and covers many different facets of planetary sciences from dust and grains, comets and asteroids, moons, minor and major planets, and everything in-between. I really enjoy the variety of science that gets presented at this conference. In the morning you could be attending a series of talks about the Martian atmosphere and then in the afternoon you could be listening to talks about the giant planets' moons or about the surface of Pluto! It's impossible to get to see everything you'd like to see because there are 4 different sessions held simultaneously at most points of the conference, but by jumping in and out of the sessions you can get to most things!

This year I will be attending again, and I will be presenting a scientific poster of my work. Presenting your work to the community is an important part of scientific research, both for work that is in-progress and work that is completed and published. For work in the latter category, presenting your research allows you to publicize your work and get it "out there" in the community, which can only ever be a good thing. In the former case, presenting in-progress research allows you to get feedback from the community on the work you're doing at a stage where it can influence the direction that you take it in. For example, if you've encountered an issue with your analysis, if you've found something usual or you're looking for opinions or advice, presenting your work, especially in poster-format, is a great way of getting feedback, advice, having discussions and networking with other experts in the field.




Scientific poster presentations are a little different from the classic standing-up-in-front-of-an-audience-style presentation with slides. With posters you are actually there standing by your poster and people come around and talk to you about it. Although its important to have enough information on the poster (and your contact details in case of questions) so that people can understand what you're researching, the real benefit is that you are able to interact with your audience. The poster is often used as more of a talking point, with images, graphs, figures and tables that you can refer to and point to whilst giving your "spiel". They also require a little more initiative and assertiveness in talking to people as you don't automatically have the floor and the captivated audience, you kind of have to generate your own! It's a skill that takes a bit of practice!

So what is the work I'm going to be presenting actually about? It's essentially looking at the amount of ultraviolet radiation that hits the surface of Mars. The atmosphere of Mars absorbs less UV radiation that Earth's atmosphere does because there is much less ozone present and the Martian atmosphere has a much lower pressure than that of the Earth. Why is this interesting and important to study? Well, UV radiation has a big effect on habitability (too much UV radiation and any biological materials would be sterilized) but it can also effect the chemistry that goes on on the surface - for example, UV radiation can make certain chemicals degrade. There has be previous work done looking at what happens to the amount of UV that reaches the surface when there are rock features like outcrops or overhangs creating shadows and lower UV regions, but the effect of shadowing and reflection from a spacecraft that's been stuck on the surface hasn't been investigated before, so that is what I'm doing. In close proximity to the spacecraft there will be some areas with reduced amounts of UV radiation, due to the shadowing, and other areas where the amount of radiation is increased due to the reflections.

So how have I actually gone about doing this? I've been using simulations. First I put together a simulated Martian atmosphere, containing the right levels of gas and dust (which are seasonally dependent on Mars), and find all the necessary parameters to allow my code to accurately simulate this. This model assumes that the ground is completely flat, with no features, and that the atmosphere (also flat) is made up of two different layers of gas and dust - we call this a plane-parallel code, and its an approximation that is often used for atmospheres.

 

The image above (taken from http://aty.sdsu.edu/~aty/explain/atmos_refr/models/flat.html) shows the Earth's atmosphere drawn approximately to scale so you can see it looks almost flat if you're looking at a reasonably small region of atmosphere. 

Before I could get into running my simulations to look at the ground radiation, I had to test that the code actually recreated what we see on Mars. I did this in a couple of different ways. The first was by generating a model with different amounts of dust in the atmosphere and looking at the total power received by a 1 square meter section of ground. I then compared these results to that of published and well-tested work and they agreed very well. I also tested my model against data that was collected on the surface and is publicly available and again, my model recreated this well. This gives me confidence that my model is accurately representing the Martian atmosphere!

A comparison of my model with the published results of Smith et al., 2016 Icarus 280, p. 234-248 (noted as 'DISORT' above). The agreement is good over a large range of optical depths.

So, onto my simulations! By running this code over the entire Martian year and inserting different shaped objects with different amounts of reflection into it, I can create maps of the amount of UV radiation that hits the ground in that area. An example of a flat, rectangular plate placed vertically from the ground is shown in the image below. The colour tells you the amount of radiation that is hitting the ground, with blue being the least and red being the most. This is a precursor to the simulations with other shaped objects like boxes, which I can float off the ground to imitate rovers or other spacecraft. Ultimately I want to do this with a whole variety of different shaped objects with different amounts of reflection over the whole year so I can combine them into more realistic spacecraft! If you want to know more, my abstract is here: http://www.hou.usra.edu/meetings/lpsc2017/pdf/1623.pdf. Or if you'll be at LPSC 48, come say hello!