images of stars in the background and using a sophisticated model of Hubble optics (PSF), Brown and Trujillo were able to find the best-fit disk size that would give a similar blurred image. This method was also applied by the same authors to measure the size of the dwarf planet Eris. At the time of its discovery in 2002, Quaoar was the largest object found in the Solar System since the discovery of Pluto. Quaoar's size was subsequently revised downward and was later superseded in size as larger objects (, , and ) were discovered. The uncorrected 2004 Hubble estimates only marginally agree with the 2007 infrared measurements by the Spitzer Space Telescope that suggest a higher albedo (0.19) and consequently a smaller diameter (). Adopting a Uranian satellite limb darkening profile suggests that the 2004 Hubble size estimate for Quaoar was approximately 40 percent too large, and that a more proper estimate would be about 900 km. In 2010, Quaoar was estimated to be about in diameter, using a weighted average of Spitzer and corrected Hubble estimates. In observations of the object's shadow as it occulted an unnamed 16th-magnitude star on 4 May 2011, Quaoar was estimated to be in diameter. Measurements from the Herschel Space Observatory in 2013 suggested that Quaoar has a diameter of . In that same year, Quaoar occulted a 15.8-magnitude star, with multiple positive detections yielding a mean diameter of , consistent with the Herschel estimate. Another occultation by Quaoar in June 2019 yielded a similar chord length of . Cryovolcanism In 2004, signs of crystalline ice were found on Quaoar, indicating that the temperature rose to at least sometime in the last ten million years. Speculation began as to what could have caused Quaoar to heat up from its natural temperature of . Some have theorized that a barrage of mini-meteors may have raised the temperature, but the most discussed theory speculates that cryovolcanism may be occurring, spurred by the decay of radioactive elements within Quaoar's core. Since then (2006), crystalline water ice was also found on , but present in larger quantities and thought to be responsible for the very high albedo of that object (0.7). More precise observations of Quaoar's near infrared spectrum in 2007 indicated the presence of small quantities (5%) of solid methane and ethane. Given its boiling point of , methane is a volatile ice at average surface