They have a different structure and lower mass than our galaxy. There are two other big differences. First, they are gas-rich; they have more hydrogen and helium compared to the Milky Way. They are also more metal-poor than the Milky Way. The youngest stars in the LMC and SMC have less than half the amount of other elements. Both are noted for their nebulae and larger numbers of young stars. Like our own Galaxy their stars range from the very young to the very old, which shows the Clouds have a long history.