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T. Sekiguchi, H. Boehnhardt, C.E. Delahodde, O.R. Hainaut (ESO)
The Trans-Neptunian Object 1996~TO66, one of the largest known, has been observed in great detail by our group since 1997. At the previous DPS meeting, we reported a very strong change in the shape and amplitude of this object's light-curve, that occured between Sep.1997 (when it presented traditional double-peaked lightcurve with an amplitude of 0.12~mag) and Sept.1998 (single-peaked lightcurve, amplitude=0.3mag). We discussed (Hainaut et al. 2000, A&A 356, 1076) various possible explanations for this change, and favoured a short-lived cometary outburst.
We re-observed 1996~TO66 in Nov. and Dec. 1999 using on of ESO's 8m VLTs at Paranal, with the FORS1 instrument, to monitor the changes on this object. Combining the data from both runs, we obtained a complete lightcurve coverage, showing again a single-peaked lightcurve, with an amplitude of 0.21mag (in R). This confirms the reality of the change observed between 1997 and 1998, and indicates that the evolution has not stopped yet.
Because of the large collecting area of the VLT and of the excellent image quality of the images, we could search the co-added frames for {\em very} faint coma around the object. No activity was detected. We will discuss possible causes and consequences of this evolution of the TNO surface properties.