Jupiter's many moons can be broken into two main groups

• The 8 regular satellites in prograde and approximately circular orbits, comprising the four well-known Galilean moons and the four inner moons
• A large number of irregular satellites. These are generally small and in distant, eccentric and often retrograde orbits

The largest irregular satellites, Himalia and Elara, are relatively bright and were discovered photographically early in the 20th century. The smallest, measuring about a kilometer across and appearing at magnitude 23-24, were only observed in the 21st century using 4 m or larger professional telescopes. The wide range of observing difficulty makes Jupiter's irregular satellites an interesting imaging challenge.

The Natural Satellites Ephemeris Service of the Minor Planet Center (MPC) provides accurate position and motion information for all of Jupiter's irregular satellites. Images of the 8 brightest irregular moons were collected on the nights of 28th August, 1st October and 16th November. Thirty one-minute subs were collected for Himalia, Elara, Pasiphae, Sinope, Lysithea and Carme. For the fainter moons Ananke and Leda, 90 one-minute subs were collected.

A custom workflow was developed to produce aligned images that correct for the moons' motions against the background stars:

• Calibrated and registered sub-frames were produced using Deep Sky Stacker
• The first sub-frame was plate solved using ASTAP to determine the frame center, orientation and image scale
• A custom program written in MATLAB calculated offsets for subsequent sub-frames relative to the first using the known time between frames and the satellites' motions taken from MPC. These offsets were applied to stack the registered sub-frames from DSS
• To correct for the substantial light scatter from Jupiter, a low-pass filtered image was subtracted from the original
• A 5 x 5 arc min portion of the final image centered on the ephemeris location of each moon was selected

The composite picture shows the results for the 8 imaged satellites. The low-pass filtered images were subjected to a simple linear stretch. The same stretch is used for JVI - JXI; a 10x harder stretch is used for JXII and JXIII due to their lower brightness. No other image processing has been used. The low-pass background removal produces the dark artefacts that can be observed around the brighter stars.

Dates and times shown at the top of each panel are UTC for the start of the observation. The yellow crosshairs are centred on the predicted ephemeris positions and are in excellent agreement with the observed locations. Background stars are streaked by the stacking process. The break in the star tracks for Lysithea is due to a meridian flip occurring midway through data collection. 

An attempt to image Themisto on Nov 16th was unsuccessful. One-minute subs were collected for 2 hours and processed in the same way, but no evidence for the moon could be seen. At this time Themisto was at magnitude 20.6 and lay only 28 arc min from Jupiter, making it strongly affected by glare from the planet. Close to opposition in 2023 it will reach a distance of 48 arc min and a magnitude of 19.9 and so should be achievable. I suspect this will be the limit for a 4" scope as the next two irregular moons (Callirrhoe and Megaclite) are more than a magnitude fainter.