  The Gaia Data Release 2 provides a parallax of 0.734+/-0.073 mas for SDSS
J102915+172927, currently the most metal-poor known object. This parallax
implies that it is dwarf star, ruling out the scenario that it is a subgiant.
The subgiant scenario had as a corollary that the star had been formed in a
medium highly enriched in C, thus making line cooling efficient during the
collapse, that was also highly enriched in Fe by Type Ia SNe. This scenario can
also now be ruled out for this star, reinforcing the need of dust cooling and
fragmentation to explain its formation.
