There have been four other binary trans-Neptunians (also called Kuiper belt objects) discovered: 1998 WW31, 2001 QT297, 2001 QW322, and 1999 TC36.
The raw data were collected on 2 orbits spanning about 45 minutes on UT 2001 Dec 22.536 and UT 2001 Dec 28.411 with the Hubble Space Telescope (HST) STIS instrument. Below is a movie of the 16 raw images collected. There are many cosmic rays (white "static") and CCD defects (white background pixels) apparent. The CCD defects move at about the same rate as background stars would if any were any in the image. The trans-Neptunian 1998 SM165 appears in the center, with its companion towards the right. In these images, North is 23 degrees clockwise from vertical (due to the HST rotation angle). You can see the companion "jump" between the two visits because of the long (about 6 days) timebase between visits.
Each of the 2 processed images are the median combination of the eight images taken each day after subtracting background sources. The two processed images appear below with logarithmic scaling to emphasize the companion, which is about 6 times fainter than the primary (about 15 times less massive, assuming they are made of the same material). The HST STIS instrument has pixels that are 50 milli-arc-seconds (mas) in angular size, which corresponds to a physical size of about 1300 km (810 miles) in these images. The objects are both smaller than a single pixel; the brighter object is probably less than 500 km (300 miles) in diameter. The objects look larger than one pixel because of the optics in the telescope. Between the two visits (which are 6 days apart), the companion moves about 2 pixels (2600 km = 1600 miles = about the distance between Los Angeles and Chicago). That's an average of about 10 miles per hour.
2001 Dec 22.536 (Universal Time), 205.6 +/- 0.9 mas separation (5200 km or 3300 miles).
2001 Dec 28.411 (Universal Time), 233.4 +/- 1.2 mas separation (6100 km or 3800 miles).
email: trujillo at gemini dot edu