From the October 2008 issue

Could a dwarf galaxy merging with the Milky Way have triggered the solar system’s formation?

Charles J. Waltermann, Richmond, Indiana
By | Published: October 27, 2008
It’s unlikely. Such mergers occur at speeds measured in hundreds of thousands of miles per hour. In contrast, the Sun is moving at only 38,000 mph (61,200 km/h) relative to the average motion of the Milky Way’s stars. This is no faster than random motions of the galaxy’s interstellar gas clouds. If the solar system were related directly to a galaxy merger, it would probably be moving faster than random background motions.Moreover, the Sun’s motions are similar to those of native gas clouds. This…