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(Thread) Last week, data from the Juno spacecraft's JIRAM instrument from its Jupiter encounters on Feb 17 (PJ25) and Apr 10 (PJ26) of this year arrived in the PDS so I thought I would talk about the Io data from this release. (1/n)
JIRAM stands for the Jovian Infrared Auroral Mapper. The instrument is designed to observe the thermal emission from inside Jupiter (it releases more heat than it receives from the Sun) and emission from its polar aurorae (2/n)
It has two sensors: a slit spectrometer that acquires spectra between 2–5 µm and an imager that takes L- and M-band framing images (3.455 µm and 4.78 µm center wavelengths respectively). For this thread, let's look at data from the imager (3/n) https://twitter.com/jccwrt/status/984075494449664001
While it is designed to look at Jupiter, the JIRAM team has been acquiring images of Io when the satellite passes through its field-of-view (the spacecraft doesn't turn to specifically target Io). Images of Io have been taken on 12 of the 26 orbits currently in the PDS (4/n)
These images allow us to monitor Io's volcanic activity over multiple time spans, from the 54-day span between encounters down to the 30-second span between images. For this thread, we will be looking at summed images, combining 4 or 5 separate frames to reduce noise (5/n)
So let's take a look at images from the two most recent orbits to be archived: PJ25 and PJ26. PJ25 provided Juno's closest encounter with Io to date at 200,000 kilometers, with JIRAM taking its highest resolution images of Io with a top resolution of 48 km per pixel (6/n)
These images were taken while Io was in Jupiter's shadow, allowing faint hotspots to be seen across the entire disk instead of being drowned out by reflected sunlight. Each of these hot spots is an area of thermal emission from cooling lava flows or lava fountains (7/n)
Some extended flows have several hotspots associated with them. For example, Lei-Kung Fluctus, Io's largest active lava flow field, has at least 8 hotspots associated with it in the PJ25 data (~12 have been observed over the course of the Juno mission) (8/n)
The brightest spots in the PJ25 data include Loki, Girru, (-8,275), Amaterasu, Kinich Ahau, Chalybes, Vivasvant, and Isum. The high resolution allows us to distinguish Girru from East Girru (an area that saw high activity during the NH flyby) and Isum from its tail (9/n)
PJ25 was also the first orbit where JIRAM looked at Io during two observation periods. The second took place 9 hours after the first, from a distance of 515,000 kilometers. The brightest hot spots here are Loki, Masubi, Kurdalagon, and two volcanoes surrounding Lerna Regio (10/n)
A volcano at 8S, 275W became much fainter between the two observation periods. Last week I suggested that this could be due to diurnal tidal stresses, but the southern rim of the patera obscuring the hottest components of the eruption is a likelier explanation. (11/n)
Here's a map of the hotspots seen during the two observation periods of PJ25. The colored dots reflect the intensity of the hotspot: yellow for the brightest hotspots to red to teal to blue for the faintest (12/n)
PJ26 was a more distant encounter at 250,000 kilometers, but the resolution was still quite good at 60 km per pixel. Shown here is the L-band data, which nicely shows off large-scale albedo features on the dayside as well as some hotter hot spots (13/n)
And here is the M-band image from PJ26. The brightest hotspots include Loki, Surt, Chalybes, Dusura, Uta, Zal, East Grian, Janus, Kinich Ahau, and (-17,22) (14/n)
The most interesting hotspot is Surt. Back in April, JunoCAM data suggested that there might be a red ring around Surt, which can be created by a sulfur-rich plume. While Pele's red ring is best known, they also form around outburst eruption sites. (15/n)
And sure enough, the level of thermal emission at Surt increased dramatically between PJ25 and PJ26, suggesting that Surt had undergone a major eruption between February and April. (16/n)
I think that's it for these two encounters. After PJ26, there should be more Io data from PJ27 (in the PDS in February) and after that there will be a lull of a few orbits. Still, always exciting to get more spacecraft data of Io! (17/n)
Credit for most images in this thread: NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM/Jason Perry (18/18) (/endthread)
