The virial mass of the Andromeda Galaxy is of the same order of magnitude as that of the Milky Way, at 1 trillion) solar masses (2.0×1042 kilograms). The mass of either galaxy is difficult to estimate with any accuracy, but it was long thought that the Andromeda Galaxy is more massive than the Milky Way by a margin of some 25% to 50%. This has been called into question by a 2018 study that cited a lower estimate on the mass of the Andromeda Galaxy,[12] combined with preliminary reports on a 2019 study estimating a higher mass of the Milky Way.[13][14] The Andromeda Galaxy has a diameter of about 220,000 ly (67 kpc), making it the largest member of the Local Group in terms of extension, if not mass.