Note that the orbital perturbation of Juno in 1839 was of rather low magnitude, and could have been caused by an asteroid as small as ~1km diameter. Based on cu

Note that the orbital perturbation of Juno in 1839 was of rather low magnitude, and could have been caused by an asteroid as small as ~1km diameter. Based on current models, there are potentially more than a million rocks that big in the belt still undiscovered.