The Growth of Cosmic Dust Grains

Rocky planets are thought to form through the random collision and sticking together of what are initially microscopic particles in the disc of material around a star. These tiny grains, known as cosmic dust, are similar to very fine soot or sand. Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have for the first time found that the outer region of a dusty disc encircling a brown dwarf — a star-like object, but one too small to shine brightly like a star — also contains millimetre-sized solid grains like those found in denser discs around newborn stars. The surprising finding challenges theories of how rocky, Earth-scale planets form, and suggests that rocky planets may be even more common in the Universe than expected.

This video starts with a broad panorama of the spectacular central regions of the Milky Way seen in visible light. It zooms in to the Rho Ophiuchi star-forming region, to the brown dwarf ISO-Oph 102, or Rho-Oph 102. Then, an artist’s impression shows the disc of material around the brown dwarf, and zooms in to show how tiny grains collide and stick together, to form large grains.