A Summary of a P4 Summer
At the end of August, Chuhong Mai presented a summary and results from her undergrad summer research internship at the Institute of Astronomy Astrophysics, Academia Sinica working with Meg on Planet Four. You can learn more about Chuhong here.
Chuhong spent July and August in Taiwan working on map projecting HiRISE images and exploring frost features. She kindly agreed to share her final presentation talk slides (see below) and some text to describe each slide. Thanks Chuhong for all your help this Summer!
Mars has a very thin atmosphere, 96% of which is . Every year, the two poles of Mars participate in the gas exchange of atmosphere. Since the south pole contains a lot of , it plays an significant role in Martian atmospheric dynamics.
But what’s really interesting is we observe fans and blotches appear in early spring and disappear in summer each year on the south pole. Araneiform features or ‘spiders’, which are radial channels that converge in the center, often accompany those dark stuff.
These features are everywhere from -70 to -87 deg. and not limited to the ‘cryptic region’ (low temperature because of dry ice, low albedo caused by translucent ice layer) as thought before. We use solar longitude (Ls) to measure time on Mars, these features appear from Ls 170 to Ls 300 typically.
- In the southern winter, in the atmosphere tends to condensate and dust grains serve as condensation nuclei. They fall onto the ground with and thus are embedded in the slab ice later. In spring, they are heated by the sun and heat the surrounding ice subsequently. These ice sublimate and form bubbles which then sink through the ice layer.
- With bubbles accumulate in the bottom, pressure between ice layer and the ground increase, so the ice could break and then jets of gas, together with dust, come out.
- Due to local topography and wind, the jets form fan-shaped deposits.
The gas beneath the ice layer might carve the Mars surface and form ‘spiders’.
We now have a powerful instrument to study such features. The HiRISE camera on MRO has resolution as high as 0.25m per pixel and excellent SNR (100:1). So we can study sub-meter objects like boulders on Mars. It’s able to observe same locations at different time and thus show the evolution of the south pole. It has finished 4 seasons of observation. Season is 2006-2007, season 2 is 2008-2009, etc.
This schematic show you what the focal plane of HIRISE is like. There are 10 RED CCDs, 2 NIR, 2 BG. So color images can be obtained in the middle of the focal plane. Note that there are overlaps between every 2 CCDs.
Though we have large amount of data from HiRISE, computers are bad at recognize the features in it. Thus we invite citizens on Earth to help marking them on Planet Four. It is a project under Zooniverse. Users can use the tools in the classification interface to mark features’ sources and orientation.
The cutouts are made from RGB, non-projected HiRISE products. Most people are able to make reasonable markings, and the clusters of people’s markings are recorded as pixel position. So we need to convert pixel position to latitude & longitude
. We have 2 types of data but we only use the raw data (EDR). Only map projected products of Reduced data (RDR) have spacecraft information with them. As we actually need position information of non-projected products (they are where the Planet Four cutouts come from), we decided to reassemble mosaics using raw data.
The tool we used, ISIS, is a free, specialized, digital image processing software package developed by the USGS for NASA. It is able to process data from NASA and International spacecraft missions including HiRISE. With applications in ISIS, we could follow the whole process presented here.
Now, we are able to grab position information of any point. By getting the central points of HiRISE images, we have the distribution of them in a polar view. By drawing the images’ outlines, we show the overlap of different HiRISE images, which were taken at different periods. Study on a point in the overlap region will give the time evolution of it.
We can use these data to study fans with frost, which are common in early spring. The latest hypothesis is that the blue color is caused by a change in the structure of the ice caused the the fan particles sinking into the ice. Yet there is little evidence of it.
Firstly we need to review certain amount of cutouts with frost in it. The review pool is the cutouts tagged as ‘frost’ or ‘blue’… in Planet Four Talk. Though they are not all the cutouts with frost, but there are still a large amount and might contribute to revealing secrets of frost fans.
Next, we combined several types of frost fans together and took a clearer look at how the locations of frost relative to fans change. We found that frosts only appear very early and then nearly all of them become outside of fans later.
Only point B is presented since it has beautiful overlap. The table shows how the type of frost fans changes over time. Font color represents the typical color of frost or fans at corresponding time. This series of pictures are of the same region. At the very beginning, nothing’s there. Gradually, we can see some dark blue stuff appear around the vents. They then expand to the outside and become bright blue. After that they begin to disappear, and the whole surface becomes white soon, with dark cores left
Another series show the similar process. Actually, we observe such process not just in B region. So we might have a general idea of frost evolution, as the slide shows. Interesting ‘dark rings’ are observed after frosts disappear in some places. It is the first time we see such features.