Cosmic dust – also called extraterrestrial dust, space dust, or star dust – is dust that occurs in outer space or has fallen onto Earth. Most cosmic dust particles measure between a few molecules and 0.1 mm (100 μm), such as micrometeoroids and meteoroids. Cosmic dust can be further distinguished by its astronomical location: intergalactic dust, interstellar dust, interplanetary dust, and circumplanetary dust. Information on the nature of dust in locations beyond the Solar System is mostly obtained by methods of observational astronomy, such as photometry, polarimetry and infrared spectroscopy. Direct methods are also available for the collection and study of space dust within the Solar System. For example, the Stardust spacecraft collected cometary dust, and also detected some particles of probable interstellar origin, returning samples to Earth in 2006.