NASA launched the Stardust spacecraft in 1999, with a mission to collect cosmic dust as well as dust from the comet Wild 2. It returned to Earth in 2006, and scientists and volunteers have been systematically analyzing images in an effort to identify the materials collected ever since. They have now identified seven particles that could be interstellar dust. A paper about the research has been published in Science, and 30,000 citizen scientists are listed as coauthors. An additional twelve papers will appear in the journal Meteoritics & Planetary Science.

Stars forge elements in their cores through nuclear fusion over the course of their lives, and certain stars shed these elements as interstellar dust. When a star explodes and goes into a supernova, immense quantities of elements are scattered throughout the Universe. This “stardust” provides the basis for elements essential to life, like carbon, oxygen, and nitrogen. Studying the dust particles themselves could provide critical information about how interstellar dust is formed and how it changes over time. 

During its mission, Stardust used aerogel and aluminum foil collectors about the size of a tennis racket to obtain the dust samples. Upon its return, an automated scanning microscope took images of all of the collectors inside of a clean room in order to ensure the samples had not been contaminated. 

In order to analyze the incredible amount of images and locate the particles for study, the Stardust@home project called for volunteers known as “Dusters.” Once a potential particle is spotted by a number of volunteers, a team from University of California, Berkeley verify its existence and can begin testing the dust. These particles are extremely small, ranging from about 0.2-2 microns in width, so finding and testing them is no small task.

"These are the most challenging objects we will ever have in the lab for study, and it is a triumph that we have made as much progress in their analysis as we have," Science paper co-author Michael Zolensky told NASA. 

Three of the seven particles that are candidates for interstellar origin have traces of sulfur, which could be problematic. There is some debate about whether or not those compounds could really be found in interstellar dust. However, the researchers have found an astounding amount of diversity between these dust particles in terms of composition, size, and crystal structure. The researchers need to study more particles before any of them can be definitively claimed to be of interstellar origin or not.