| Dust cloud motion on Mars - 2018 data reworked by N.MacNeill |
With cloudy weather comes the opportunity to reprocess old data. So no Greg, I have not lost interest in Venus, I just can't see through clouds. :-D On July 9th 2018, we were 18 days from the Mars Opposition and this was going to be a perihilic one, the best since 2003. A global dust storm had swept the planet since May 31st where it had started in the Acidalia Planitia. The dust storm was close to its peak at this time. I had excellent seeing and made 8 successive RGB and IR (642nm BP) captures of 4 mins duration each over 2.5 hours. Perhaps stupidly I made the first runs with my OSC camera, the ZWO ASI 1600MC, before switching over to my standard monochrome RGB rig (ZWO ASI 174MM, Chroma RGB filters, Tele Vue 2.5X powermate). This first run was therefore of significantly lower quality than the others. When I first published an animation of the planet's rotation on AstroBin, Ethan Chappel made the observation that he thought he could see the dust clouds moving. This is very subtle and difficult to spot with the planet's rotation, so I take my hat off to him for his powers of observation. Upon examining the animation I was able to confirm the dust cloud movement. I then set about making planetary maps in WinJUPOS to convert the orthographic projection of a sphere viewed at an infinite distance, to the equirectangular projection (planetocentric latitudes), necessary to freeze the static features such as volcanoes and to allow any dust movement to be more readily seen. With the benefit of 5 years more planetary image processing experience I felt I could do a better job with the image processing and thus the quality of the animation. Recently I set about completely reprocessing the data. I decided to work on the OSC capture to see if I could generate an extra data point by having it more closely match the monochrome RGB output. I included this in the planetary maps but not of the footage where the planet's rotation is seen. This animation therefore combines the colour (RGB) and IR data sets in sequence. Each starts with a view of the planet's rotation (north up), then shows an animation of, firstly the broader planetary maps, then the cropped-in central area. The animation sequences are quite quick, with 0.1 secs per frame, in order to allow the motion to be more clearly seen and to flow smoothly, although the start frames are of longer duration. However, remember that the real duration of these sequences was more like 2.25 hours. It was interesting to see the clouds moving at the periphery of the planetary maps that I had not seen previously, given I had cropped in so much. To my knowledge this is the only footage taken from the Earth where dust clouds on Mars can be seen to move, although I believe such motions have been recorded by spacecraft in orbit, but perhaps not on a planet wide scale like this. I measured the speed of the cloud front movement at ~ 100 km/hr, which is apparently close to the maximum wind speed limit on Mars. Dust cloud motion on Mars - 2018 data reworkedALPO-Japan Latest