JunoCam "Marble Movie" data available
Posted by Emily Lakdawalla
22-08-2016 16:56 CDT
Since a few days after entering orbit, JunoCam has been taking photos of Jupiter every fifteen minutes, accumulating a trove of data that can be assembled into a movie of the planet. This first orbit of Jupiter was a very long one, taking Juno more than 10 million kilometers away. Because JunoCam is a wide-angle camera, Jupiter appears tiny from such a great distance. Fortunately, Jupiter is colorful enough that it's not featureless, even when it appears so small; you can see its red belts and occasionally the red spot show up in the photos. The JunoCam team is calling the movie taken from this first long orbit the "Marble Movie," because that's what Jupiter looks like, a little rolling marble.
The JunoCam team has released the first month's worth of Marble Movie data in two large chunks. Space imaging enthusiast Gerald Eichstädt has developed an automated routine to process those chunks of data, producing thumbnails, which means I can now post one of my browse indexes to all the data.
Jupiter doesn't look too impressive in these pictures; the best thing to do is to animate them. Gerald is working on just such an animation. Below is a preliminary version of his work with the data, covering the period up to August 11 (the most recent data currently available). In this movie he's aligned all the color channels and has emphasized the moons, but he hasn't yet taught his algorithm how to handle the appearance of the moons as they cross the disk of Jupiter. The moons are only barely detected by JunoCam and are (in the original data) less than a pixel across; at times they appear to wink out or twinkle because they weren't bright enough in some frames to be detected by Gerald's algorithm. They may also disappear where they pass into Jupiter's shadow.
A couple of other peculiarities about the data: Initially, they alternated blue-filter and RGB images as they took one photo every 15 minutes, so the frames of this animation are spaced half an hour apart (since Gerald used only the RGB frames). Then they went through a period where it was just RGB every 15 minutes, which means Jupiter's rotation appears to slow down. Finally, there was a period alternating methane-filter and RGB images, so the rotation speeds up again. There were two gaps in the data on July 14, making for a couple of little jumps in the animation. As always, watch for transits of moon shadows and moons themselves across Jupiter's disk. If you watch closely, you'll see Ganymede transit the disk at the same time that Io's shadow does!
These are sort of cool to play with but the real fun is going to come after this weekend. Juno is now picking up speed as it approaches for its first close approach to Jupiter since entering orbit. Perijove 1, as the mission calls it, will happen on August 27. All the science instruments will be taking their very first close-up data on Jupiter. I can't wait to see JunoCam's close-up images! In the meantime, check out my Marble Movie data browse page and stay tuned to the JunoCam website for the latest pictures.