Since Quaoar is not in a mean-motion resonance with Neptune, it is also classified as a classical Kuiper belt object (cubewano) by the Minor Planet Center and Deep Ecliptic Survey. Quaoar's orbit is moderately inclined to the ecliptic plane by 8 degrees, relatively high when compared to the inclinations of Kuiper belt objects within the dynamically cold population. Because Quaoar's orbital inclination is greater than 4 degrees, it is part of the dynamically hot population of high-inclination classical Kuiper belt objects. The high inclinations of hot classical Kuiper belt objects such as Quaoar are thought to have resulted from gravitational scattering by Neptune during its outward migration in the early Solar System. Physical characteristics Quaoar's albedo or reflectivity could be as low as 0.1, similar to 's albedo of 0.127. This may indicate that fresh ice has disappeared from Quaoar's surface. The surface is moderately red, meaning that Quaoar is relatively more reflective in the red and near-infrared spectrum than in the blue. The Kuiper belt objects Varuna and are also moderately red in the spectral class. Larger Kuiper belt objects are often much brighter because they are covered in more fresh ice and have a higher albedo, and thus they present a neutral color. A 2006 model of internal heating via radioactive decay suggested that Quaoar may not be capable of sustaining an internal ocean of liquid water at the mantle–core boundary. The presence of methane and other volatiles on Quaoar's surface suggest that it may support a tenuous atmosphere produced from the sublimation of volatiles. With a measured mean temperature of ~ , the upper limit of Quaoar's atmospheric pressure is expected to be in the range of a few microbars. Due to Quaoar's small size and mass, the possibility of Quaoar having an atmosphere of nitrogen and carbon monoxide has been ruled out, since the gases would escape from Quaoar. The possibility of a methane atmosphere, with the upper limit being less than 1 microbar, was considered until 2013, when Quaoar occulted a 15.8-magnitude star and revealed no sign of a substantial atmosphere, placing an upper limit to at least 20 nanobars, under the assumption that Quaoar's mean temperature is and that its atmosphere consists of mostly methane. The upper limit of atmosphere pressure was tightened to 10 nanobars after another stellar occultation in 2019. Mass and density Because Quaoar is a binary object, the mass of