Head in the Martian Clouds: a Research Update

 

As Conor mentioned a few posts ago, just because a mission ended in the past doesn't mean that all the useful science from that mission has been extracted. This week, Grace tells us about some research she has been completing applying new models to old data in order to make new discoveries. I have a particular affinity for this kind of science. Truly, it justifies the investment made to keep a record of all data returned from other planets and to make that data available to anyone with a theory to test. In a way, it reminds me of the curation of returned samples, only a fraction of which are consumed by the planned laboratory testing once they are returned to Earth. A portion of each sample is held back, waiting for future questions, theories and experimental techniques to be invented that will unlock mysteries unknown to present-day planetary science. The Image above of the Phoenix Lander at Green Valley, Mars is credited to Corby Waste (NASA/JPL). This image was created prior to landing and therefore is missing the periglacial features that were seen at the actual landing site. It's based off a famous image from a previous rover.

 

By Grace Bischof 

Over the past couple of weeks, I have been wracking my brain to come up with a good topic to write about for my round of the blog post. I realized I am now just shy of my first-year anniversary as a PVL member (where did the time go!?). With a little experience under my belt, I figured it would be a good time to finally give an update on the research I’ve been doing over the last year – and especially the past 8 months. Since I had no classes to worry about, I could dedicate the majority of my working hours to my project. 

The project I’ve been working on was originally assigned to me with a need for a project to work on from home. My initial project – MAGE – which I briefly talked about in my introductory blog post last year, is all lab-based. Obviously, with multiple lock-downs and very limited access to campus, I have not been able to work on MAGE. Thus, the Phoenix project was born. 

To start, the Martian atmosphere is very thin, and has a weak greenhouse effect compared to Earth. The daily temperature on Mars is essentially mediated by visible-band radiation coming in from the sun, where it is absorbed by the surface, then re-radiated back into space as thermal radiation. Aerosols in the atmosphere – in the form of dust or water-ice particles – can produce a secondary effect on the temperature. Water-ice particles scatter a portion of the incoming solar flux and, importantly to this project, absorb and reflect outgoing longwave flux. This increases the thermal radiation at the surface, which can increase warming.

This work is dubbed “the Phoenix project” because it is based on the Phoenix mission, which landed on Mars in 2008. The Phoenix lander was, and still is, the most northern-based lander on Mars, where it was equipped with instruments to study the local meteorology and water cycle in the Martian polar region. Phoenix operated for 150 sols, beginning at the end of northern Spring, and carrying through summer solstice into the mid-summer. During its mission, Phoenix made many detections of water-ice clouds, fog, and made the first observation of water-ice precipitation on Mars.

So, how does this all relate? Well, while the LIDAR and camera onboard the lander captured important information about the clouds near Phoenix, these instruments could only operate for a small fraction of the entire mission length. On the other hand, the temperature sensors on the lander made near-continuous observations for the entire mission, measuring the atmospheric temperature every 2 seconds. Since we know that clouds can have an effect on the temperature, by modelling the atmospheric temperature at the Phoenix site, we can create a full record of the cloud activity.

Building the cloud record involves using a surface energy balance at the location of the lander. This includes all energy flux components that will influence the temperature, such as radiative effects of dust in the atmosphere. The energy balance contains one parameter, R, which is solely attributed to the flux reflected by water-ice clouds. The ground temperature is modelled using a subsurface conduction scheme involving various regolith properties, and the atmospheric temperature is found by an equation involving the ground temperature and the sensible heat flux. R is then determined by comparing the modeled air temperature to the air temperature collected by the temperature sensor aboard Phoenix. If the temperatures are a perfect match, R = 0 over the entire run, and it is assumed no clouds are present. Otherwise, the temperatures are matched by varying R on 2-hour intervals within the model. 

Completing this analysis for every sol of the mission builds up a continuous picture of the reflected flux throughout the mission. The reflected flux can be related to cloud properties such as optical depth and ice-particle radius. This is the portion of the project I am currently working on. I believe this project has helped strengthen my research skills, as the methods went through several iterations in the beginning and we had to work through many problems that were occurring. While this isn’t the project I was given initially, I have really enjoyed the time I’ve spent working on the Phoenix project and my enthusiasm for Martian meteorology has really grown.