Primitive Dust Samples Provide Pre-Solar Time Capsules


An international team of scientists has found some of the most primitive matter containing abundant interstellar material analyzed to date amongst dust particles collected from the upper atmosphere by NASA aircraft. The samples were gathered in April 2003 during the Earth's passage through the dust stream left behind by comet 26P/Grigg-Skjellerup. Dr. Henner Busemann of the University of Manchester will present the results at the European Week of Astronomy and Space Science at the University of Hertfordshire on Tuesday 21st April.

"We found an extraordinary wealth of primitive chemical "fingerprints", including abundant pre-solar grains, true stardust that has formed around other earlier stars, some during supernova explosions, associated with extremely pristine organic matter that must pre-date the formation of our planets," said Dr. Busemann.

Interplanetary dust particles showing pre-solar silicate grains and organic matter of interstellar origin. Credit: H Busemann.

The interplanetary dust particles, which are only a few thousands of a millimeter in diameter, were analyzed by an international collaboration from the UK, the US and Germany. Two grains appear to have percentage levels of material thought to match the nebula from which the Solar System formed. One dust particle contained four pre-solar silicate grains with an unusual chemical composition that matches predictions for silicates formed from cooling gas following a supernova explosion. One of these grains, a fragment of olivine, was found next to a hollow, globule of carbon, most likely of interstellar origin. Organic coatings are suspected to be the time-capsules that protected and secured the survival of some of these fragile stellar silicate grains in the radiating space environment.

"These tiny grains combine all the most primitive features, found to date only separately in various meteorites, samples from the Stardust mission and interplanetary dust particles. The particular collection scenario allows us speculate that we truly have samples of a known source, comet Grigg-Skjellerup, in our hands," said Dr. Busemann.

Interplanetary dust particles showing pre-solar silicate grains and organic matter of interstellar origin. Credit: H Busemann.

The group compared their findings with Deep Impact observations of comet 9P/Tempel 1 and analyzes of samples from comet 81P/Wild 2 collected by Stardust. The comparison revealed surprising differences between the comets, which are all short-period comets with orbits constrained by Jupiter's gravitational field. Comet 81P/Wild 2 was found to have incorporated much higher levels of material formed in the inner Solar System, however all the comets contained materials such as carbonates that commonly indicate the presence of water.

The primitive matter, containing unaltered samples of the building blocks of our Solar System, gives insights into the turbulent processes leading to the formation of our Solar System and also the fate of comets orbiting since their formation at the outer edges of our planetary system. While the planets in the inner solar system, such as Earth or Mars, once experienced harsh conditions and have changed substantially over the past 4.5 billion years, comets are believed to store the original material of the early Solar System, acting as 'supersized refrigerators'.

"We still have much to learn from samples of primitive matter containing large amounts of interstellar grains. Aircraft offer a less costly way to collect cometary dust, albeit of unknown origin. Predictions and timed collection campaigns in the future offer an increased likelihood to analyze material from known comets without actually going there," added Dr. Busemann.

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