In this paper, we prove that the Hilbert scheme H₄ (X₅) of rational quartic curves on the quintic del Pezzo threefold X₅ is isomorphic to a Grassmannian bundle over the Hilbert scheme of lines on X₅. In particular, H₄ (X₅) is smooth and irreducible. Our approach builds upon the geometry of rational quartic curves on X₅ studied by Fanelli-Gruson-Perrin in their work on the moduli space of stable maps to X₅.
Chung et al. (Wed,) studied this question.