Affine Grassmannians for G_2

We study affine Grassmannians for the exceptional group of type G_2. This group can be given as automorphisms of octonion algebras (or para-octonion algebras). By using this automorphism group, we consider all maximal parahoric subgroups in G_2, and give a description of affine Grassmannians for G_2 as functors classifying suitable orders in a fixed space.