The Andromeda galaxy is approaching the Milky Way at about 100 to 140 kilometres per second (62 to 87 mi/s), so it is one of the few blue shifted galaxies. The Andromeda galaxy and the Milky Way are thus expected to collide in perhaps 4.5 billion years. The Milky Way–Andromeda collision is likely to make the galaxies merge, to form a giant elliptical galaxy. Such events do happen in galaxy groups. However, 4.5 billion years is a vast period of time, roughly equal to the time the Earth has existed as a planet.