MATRIX: SPACE DUST
1.5mm track of a meteoroid captured in aerogel
Credit: ESA, NASA
SOME METEORITES ARE MADE PRIMARILY OF TINY PARTICLES OF DUST—FROM OUR SOLAR SYSTEM AND BEYOND.
THE VOID OF OUTER SPACE IS NOT SO EMPTY AFTER ALL: the galaxies are awash in tiny mineral crystals, known commonly as dust grains. In the early history of our own solar system, dust particles orbiting around the growing Sun collected into larger clumps and collided with bigger objects, serving as a kind of glue to trap and bind everything together. This dust has been preserved as the dark, fine-grained material surrounding chondrules and CAIs that is known as the matrix of a meteorite.
The composition of the matrix varies, but in some meteorites, it is rich in carbon compounds and water—chemicals that are necessary for life on our planet. Some meteorites even contain dust from other stars. Scientists do not know the precise ages of these "presolar grains" but have determined that they are older than the Sun itself.
SAMPLES OF STARDUST
10 micron interplanetary dust particle
Credit: NASA
As stars age, they spew out great quantities of dust grains into interstellar space. Early in our solar system's history, dust that formed around stars older than the Sun reached the solar nebula and mixed with chondrules, calcium-aluminum inclusions (CAIs) and dust particles from our solar system.
Today, small amounts of this stardust, known as presolar grains, can be found in some meteorites. The Allende meteorite contains many types of presolar grains, including tiny diamonds that consist of only about 1,000 carbon atoms. This vial contains about 60 quintillion (6 followed by 16 zeros) of these "nanodiamonds," isolated from a fragment of Allende similar in size to the 5.7-gram (0.013-pound) piece displayed here.
The microscopic nanodiamonds in Allende consist of roughly 1,000 carbon atoms each. These atoms exist in a regular crystal structure that can be seen with a high-powered microscope.
At the end of its active life, a star sometimes explodes violently in a supernova. In 1987, astronomers captured this image of a star before the explosion and after, when the star was at or near its peak brightness. Analysis of isotopes of the elements carbon, silicon and nitrogen in presolar grains indicates that some of these grains formed in supernovas.
SIMILAR TO THE SUN
The mix of rock-forming elements in the matrix of the meteorite Orgueil is proportionally the same as that on the visible surface of the Sun. Orgueil and related meteorites formed from the same material and at about the same time as our Sun.
THE INGREDIENTS FOR LIFE?
The matrix of some meteorites contains relatively high levels of carbon compounds. These meteorites, such as Mighei, are as black as charcoal. In contrast, meteorites like Olivenza have a matrix that is relatively low in carbon and are much lighter in color.
Meteorites that are high in carbon compounds often contain relatively high levels of water as well. As our planet was forming, meteorites and comets rich in water and complex carbon compounds delivered these components to Earth, providing the chemical building blocks for life on our planet.
LOOK CLOSELY
The matrix of a meteorite often contains metals, predominantly iron. The matrix of Weldona has a high metal content, while Barratta has much less metal in its matrix. Their classification reflects these differences: Weldona is an H-chondrite ("H" for high metal) and Barratta is an L-chondrite ("L" for low metal).
HOW DO WE KNOW?
COMPARISON WITH THE SUN
Certain primitive meteorites have a chemical makeup that links them to the Sun. But no one has ever collected any material from our Sun—so how do we know what its composition really is?
Scientists have determined the proportions of the chemical elements present in the Sun using the technique of spectroscopy. Spectroscopy involves measuring how atoms and molecules reflect or absorb light. The light emitted from the Sun provides a "fingerprint" of each chemical present in the star. Careful analysis can extract these fingerprints from sunlight.
Our Sun formed about 4.6 billion years ago from a mixture of chemical elements that is proportionally similar to that found in certain ancient meteorites. Indeed, if you could cool the Sun to a solid you could hold in your hand, the resulting rock would be a carbon-rich chondrite, like the meteorite Orgueil.
