Inside a meteorite found in Antarctica lies a pink grain of the mineral spinel. Such grains are rare in ureilites, and this one grew to half a millimeter. It is like a time capsule: it froze when the parent asteroid was still cooling after its birth.
The oxygen isotopes in the spinel match those of other ureilites — meaning the grain grew on the same body, not from space. The distribution of aluminum between minerals allowed scientists to calculate the crystallization temperature: about 1318 K. That is like a trace of a hot furnace in which the first aluminum-rich portions melted.
Why does this matter? Ureilites contain almost no aluminum-rich minerals. It was thought that early aluminum melts were completely lost during partial melting. The discovered spinel is rare evidence that such melts existed and could be preserved locally.
The spinel in EET 87720 is pink, a color visible even in polarized light — a rare sight in ureilites, where olivine and pyroxene usually dominate. A spinel grain 400–500 μm across can be compared to a grain of sand, but by ureilite standards it is a giant: typical accessory spinels in them are tens of times smaller.