Sedna has a V-band absolute magnitude (H) of about 1.8, and it is estimated to have an albedo of about 0.32, thus giving it a diameter of approximately 1,000 km.[6] At the time of its discovery it was the intrinsically brightest object found in the Solar System since Pluto in 1930. In 2004, the discoverers placed an upper limit of 1,800 km on its diameter,[25] but by 2007 this was revised downward to less than 1,600 km after observation by the Spitzer Space Telescope.[26] In 2012, measurements from the Herschel Space Observatory suggested that Sedna's diameter was 995 ± 80 km, which would make it smaller than Pluto's moon Charon.[6] Because Sedna has no known moons, determining its mass is currently impossible without sending a space probe.