Fields containing Jupiter and its moons were observed during normal survey operations by the southern 2MASS facility on 980921 and 980924. There is no guarantee beforehand that 2MASS will observe any of the planets, and this event was merely a lucky coincidence (or unlucky, considering that 18 survey scans will have to be reobserved with Jupiter out of the way). Needless to say, Jupiter is badly saturated in J and H. At Ks, methane absorption in Jupiter's atmosphere dims the planet and you can start to see some of the cloud bands. Three of the four Galilean satellites were also observed. Europa was occulted by Jupiter at the time, and Io, Ganymede and Callisto are all saturated.

An interesting question was whether or not any of the other moons fell in the observed tiles and whether or not they were visible. Using the JPL ephemeris program Horizons, I obtained predicted coordinates for the 12 minor Jovian satellites during 980921 and then searched the corresponding scans for possible sightings. I was able to find most of them. The moons that were not visible were also the smallest, and therefore the faintest, objects.

The moon Ananke was located too far from Jupiter to be observed in the range of tiles on 980921s, but the predicted location was scanned a few days later on 980924s.

The following table lists the observations of all of Jupiter's moons as observed by 2MASS. Positions for visible objects are from the 2MASS point source lists; for invisible objects, they are the predicted positions from Horizons, and are good to an arcsec or two since only the starting and ending time of the scan were readily available.

Clicking on the moon's name will in most cases display the corresponding 2MASS images. The non-observations of Ananke and Leda are also included. The images are usually centered on the moon.
 

Moon	RA (J2000)	Dec (J2000)	Night	Scan	Coadd	Notes
Io	23 34 28.22	-04 27 36.4	980921s	062	209	visible and saturated
Europa	23 34 34.05	-04 26 49.3	980921s	062	209	not visible - in occultation
Ganymede	23 34 54.96	-04 24 35.4	980921s	062	198	visible and saturated
Callisto	23 35 13.02	-04 22 23.2	980921s	069	080	visible and saturated
Amalthea	23 34 34.07	-04 26 57.0	980921s	062	209	not visible - in transit or occultation
Himalia	23 34 10.93	-03 51 40.7	980921s	061	092	visible
Elara	23 32 45.35	-04 50 37.8	980921s	058	221	visible
Pasiphae	23 42 17.26	-04 44 33.4	980921s	096	221	visible
Sinope	23 41 12.55	-04 40 11.8	980921s	087	056	visible
Lysithea	23 36 54.55	-03 40 11.5	980921s	073	103	visible
Carme	23 40 11.41	-03 38 18.4	980921s	085	103	visible
Ananke	23 29 24.23	-04 22 26.4	980924s	055	198	not visible - too faint
Leda	23 35 06.24	-04 02 51.5	980921s	069	092	not visible - too faint
Thebe	23 34 29.68	-04 27 30.7	980921s	062	209	visible between Jupiter and Io, just above Io's diffraction spike, best at Ks
Adrastea	23 34 31.99	-04 27 15.5	980921s	062	209	not visible - lost in Jupiter's glare just off western limb
Metis	23 34 33.61	-04 27 00.9	980921s	062	209	not visible - in transit or occultation

See also "Near-Infrared Observations of the Outer Jovian Satellites"
by M.V. Sykes, B. Nelson, R.M. Cutri, J.D. Kirkpatrick, R.L. Hurt and M. Skrutskie
in the February 2000 issue of Icarus.