The stardust abundance in the local interstellar cloud at the birth of the Solar System

Primitive Solar System materials, such as certain types of meteorites, interplanetary dust particles and cometary matter, contain small quantities of refractory dust grains that are older than our Solar System. These ‘presolar grains’ condensed in the winds of evolved stars and in the ejecta of stellar explosions, and they were part of the interstellar gas and dust cloud from which our Solar System formed 4.57 billion years ago 1 . Interstellar dust is not only stardust but forms in the interstellar medium as well, predominantly as silicates, and, to a lesser extent, as carbonaceous dust and iron particles 2 . Presolar grains represent a sample of stardust, and their abundances in primitive Solar System materials can be used to constrain the fraction of stardust among interstellar dust. Here we show that the size distribution of presolar silicates follows that observationally derived for interstellar dust, at least in the diameter range 100–500 nm, that current estimates of presolar grain abundances (mass fractions) are at least a factor of 2 too low, and that several per cent of the interstellar dust in the interstellar cloud pre-dating our Solar System was stardust, making it a minor but still important ingredient of the starting material from which our Solar System formed. The stardust component of interstellar dust has been quantified by analysing samples of pre-solar dust grains from meteorites and found to be at least twice as much as had been thought. The silicate portion follows the size distribution of interstellar dust.