Analysis of plasma data supplied by the European satellite ISEE 2 has confirmed the existence in the solar wind of two different ion populations (referred to as 'reflected' and 'diffuse') backstreaming from the earth's bow shock. The two populations have similar bulk velocities and flux densities but quite different temperatures. In addition, the diffuse ions strongly interact with the solar wind, producing fluctuations in the distribution of the proton velocities, while the reflected ions do not disturb significantly the incoming solar wind. The origin of the two ion populations is then discussed. Although no firm conclusion is reached, the experimental evidence seems to favor a model which explains the appearance of the diffuse population as the result of an interaction of the reflected ions with the solar wind.