Today we have a post by Candy Hansen, principal investigator (PI) of Planet Four and Planet Four: Terrains.  Candy also serves as the Deputy Principal Investigator for HiRISE (the camera providing the images of spiders, fans, and blotches seen on the original Planet Four project).  Additionally she is a  member of the science team for the Juno mission to Jupiter. She is responsible for the development and operation of  JunoCam, an outreach camera that involves the public in planning images of Jupiter.

We have discovered something very interesting in the number and size of the fans that show up on the south polar seasonal cap every spring, that you are measuring.  It turns out that in springs following both global and regional type A dust storms we see a lot more fans than normal for that time of year.  This picture compares sub-images from 7 Martian years taken in “Manhattan” at solar longitude 195-197.   The position of Mars in its orbit is the solar longitude (“L_s”), and southern spring begins at L_s 180 when the sun crosses the equator and heads south.   Mars years 29, 30 and 33 have visibly more fans.   There was a global dust storm in Mars Year (MY) 28 that started in early summer.  Intense Type A storms, which are regional and centered at high southern latitudes, took place in MY29 and MY32.  It looks like the spring after these storms have large numbers of seasonal fans.

Although the visual impression is powerful when these images are compared we can go beyond that now, thanks to the Planet Four fan catalog  that your work has populated.  We can quantify the differences. We used the MY29 an MY 30 catalog that we’ve published this year in our first paper, and also newly generated catalogs for Manhattan for MY 28, MY31, MY 32.   Instead of just saying “there are a lot more fans” we can say “there are over twice as many fans” in MY29 and MY30 compared to MY28, 31 and 32.   We do that by querying the catalog – an example is shown below.  The plot below shows numbers of fans as a function of time in the spring and we can compare 5 years at L_s 195.  I had the pleasure of presenting this (your!) work at the 2019 Lunar and Planetary Science conference last week in Houston, Texas.

To confirm that Type A storms are playing a significant role in the composition of the seasonal ice sheet that produces the carbon dioxide jets that bring up the dust and dirt that create the seasonal fans and blotches, we need to look at the number of seasonal fans and the area covered in MY33.  We only have classifications for Seasons 1-5 of the HiRISE seasonal monitoring campaign (MY28-32). This brings me to my request:  We would really like to have Planet Four measurements for MY33.  We have uploaded the images, so it is ready for you to process.  We would like to thank you in advance for your generosity with your time.   Once those measurements are in we will be ready to write our next paper documenting these findings in a peer-reviewed scientific journal.  As you know we have published one paper already and two more are in progress.  This is a significant result, and we could not have done this without all of you.

Help classify the new images of Manhattan today at http://www.planetfour.org.