Its double nature or its elongated shape did not appear to them immediately at the time of the observations, but only later during the meticulous analysis of the data.

The transneptunian objects are small bodies of the Solar system located beyond the orbit of Neptune, at more than 30 astronomical units from the Sun. They are icy bodies, very primitive as fossil remnants of the formation of the Solar system, 4.6 billion years ago.

The study of these objects, discovered for the first time less than ten years ago, is currently in full development. It can provide invaluable indices on the composition of the primitive nebula and on the processes prevailing at the beginning of the Solar system.

Moreover, the knowledge of the physical properties of the transneptunian objects could be a significant step in the study of circumstellar discs and planet formation around other stars that the Sun.

1998 WW31 like all the objects of the Solar system moves relative to fixed stars of the field. It is a weak object of 23.6 in magnitude and distant by 45.6 astronomical units from the Earth. 1998 WW31 appears undoubtedly double. The exceptional quality of the Mauna Kea site allowed the resolution of the pair.

With only the images, two alternative interpretations were possible:

They are two transneptunian objects on distinct orbits but having by pure coincidence a common apparent motion over two nights!

1998 WW31 is undoubtedly a twin (like Pluto-Charon)

It is the second alternative, much more probable than the first, which proved to be right. Indeed, the CFHT archive images of January 7 2000, made it possible to find 1998 WW31. But the orientation of the pair, as well as the separation between the two components had changed: 1998 WW31 is actually a twin!