Context : Recent results suggest that there is a group of trans-Neptunian objects ( TNOs ) ( 2003 EL _ { 61 } being the biggest member ) , with surfaces composed of almost pure water ice and with very similar orbital elements .
These objects provide exciting laboratories for the study of the processes that prevent the formation of an evolved mantle of organics on the surfaces of the bodies in the trans-Neptunian belt ( TNb ) .

Aims : We study the surface composition of another TNO that moves in a similar orbit , ( 145453 ) 2005 RR _ { 43 } , and compare it with the surface composition of the other members of the group .

Methods : We report visible and near-infrared spectra in the 0.53-2.4 \mu m spectral range , obtained with the 4.2m William Herschel Telescope and the 3.58m Telescopio Nazionale Galileo at the “ Roque de los Muchachos ” Observatory ( La Palma , Spain ) .
Scattering models are used to derive information about its surface composition .
We also measure the depth D of the water ice absorption bands and compare with those of the other members of the group .

Results : The spectrum of 2005 RR _ { 43 } is neutral in color in the visible and dominated by very deep water ice absorption bands in the near infrared ( D = 70.3 \pm 2.1 % and 82.8 \pm 4.9 % at 1.5 \mu m and 2.0 \mu m respectively ) .
It is very similar to the spectrum of the group of TNOs already mentioned .
All of them present much deeper water ice absorption bands ( D > 40 % ) than any other TNO except Charon .
Scattering models show that its surface is covered by water ice , a significant fraction in crystalline state with no trace ( 5 % upper limit ) of complex organics .
Possible scenarios to explain the existence of this population of TNOs are discussed : a giant collision , an originally carbon depleted composition , or a common process of continuous resurfacing .

Conclusions:2005 RR _ { 43 } is member of a group , may be a population , of TNOs clustered in the space of orbital parameters that show abundant water ice and no signs of complex organics and which origin needs to be further investigated .
The lack of complex organics in their surfaces suggests a significant smaller fraction of carbonaceous volatiles like CH _ { 4 } in this population than in ” normal ” TNOs .
A carbon depleted population of TNOs could be the origin of the population of carbon depleted Jupiter family comets already noticed by A ’ Hearn et al .
( 1995 ) .