  The largest bodies - or dwarf planets - constitute a different class among
Kuiper belt objects and are characterised by bright surfaces and volatile
compositions remarkably different from that of smaller trans-Neptunian objects.
These compositional differences are also reflected in the visible and
near-infrared colours, and variegations across the surface can cause broadband
colours to vary with rotational phase. Here we present near-infrared J and
H-band observations of the dwarf planet (136199) Eris obtained with the
GuideDog camera of the Infrared Telescope Facility. These measurements show
that - as suspected from previous J-H measurements - the J-H colour of Eris
indeed varies with rotational phase. This suggests notable surface heterogenity
in chemical composition and/or other material properties despite the otherwise
quite homogeneous, high albedo surface, characterised by a very low amplitude
visible range light curve. While variations in the grain size of the dominant
CH4 may in general be responsible for notable changes in the J-H colour, in the
current observing geometry of the system it can only partially explain the
observed J-H variation.
