  We present a systematic investigation of the rotational lightcurves of
trans-Neptunian objects based on extensive optical data from Mauna Kea. Four of
13 objects (corresponding to 31%) in our sample ((33128) 1998 BU48, 2000 GN171,
(20000) Varuna and 1999 KR16) were found to exhibit lightcurves with
peak-to-peak range > 0.15 magnitude. In a larger sample obtained by combining
our data with reliably determined lightcurves from the literature, 7 of 22
objects (32%) display significant (> 0.15 magnitude range) lightcurves. About
23% of the sampled objects have lightcurve ranges > 0.4 magnitudes. Curiously,
the objects are very large (> 250 km diameter, assuming an albedo of 0.04) and,
in the absence of rotation, should be near spherical due to self compression.
We propose that the large amplitude, short period objects are rotationally
distorted, low density rubble piles. Statistically, the trans-Neptunian objects
are less spherical than their main-belt asteroid counterparts, indicating a
higher specific angular momentum perhaps resulting from the formation epoch. In
addition to the rotational lightcurves, we measured phase darkening for 7
Kuiper Belt objects in the 0 to 2 degree phase angle range. Unlike Pluto, the
measured values show steep slopes and moderate opposition surge indicating
backscatter from low albedo porous surface materials.
