1. A method of navigating a space vehicle, the method comprising: receiving an image of a planet surface; processing the received image to identify a plurality of edge pixels and angle data for each of the edge pixels; using a circular mask having a radius band that includes a range of radii, filtering the edge pixels to obtain a grayscale image in which a plurality of peaks identify centers of circles having radii in the range of radii; for a given peak and its corresponding radius band, scoring the angle data for the edge pixels corresponding to the corresponding radius band; using the scoring to determine whether to accept or reject the given peak as an indicator of a circular planetary feature; using accepted peaks to identify a plurality of planetary features by shape, size, and spacing relative to other planetary features; comparing at least some of the identified planetary features with a predefined planet surface description including sizes and locations of a plurality of planet landmarks; based on the comparing, determining one or more matches between the at least some planetary features and the planet surface description; and based on the one or more matches, determining a location of the space vehicle relative to the planet.