Reflected light from sand grains in the terrestrial zone of a protoplanetary disk.

In the standard model of terrestrial planet formation, interstellar grains of typical size ∼0.1 μm are expected to grow to millimetre, centimetre or even-metre sized objects rather quickly. Unfortunately, such evolved disks are hard to observe. This paper reports observations of grains that have grown to about millimetre-size or larger in the terrestrial zone of a 3 Myr old star.