Psamathe is about 38 kilometers in diameter. It orbits Neptune at a distance of about 46,695,000 km and requires almost 25 Earth years to make one orbit. The orbit of this satellite is close to the theoretical stable separation from Neptune for a body in a retrograde orbit. Given the similarity of Psamathe's orbital parameters with Neso (S/2002 N 4), it was suggested that both irregular satellites could have a common origin in the break-up of a larger moon. Both are further from their primary than any other known moon in the Solar System.