Mystical Surprise: Spitzer Sees Quartz Crystals In Planetary Disks

by Nancy Atkinson on November 11, 2008

Crystals (insets) found in planetary disks.  Credit: Caltech

Crystals (insets) found in planetary disks. Credit: Caltech

The Spitzer Space Telescope has, for the first time, detected tiny quartz-like crystals sprinkled in young planetary systems. This surprises astronomers, because these crystals, which are types of silica minerals called cristobalite and tridymite, require flash heating events, such as shock waves, to order to form. So what is going on in these planetary disks to create this type of materials? The findings suggest that shock waves from swirling gas and dust are responsible for creating the stuff of planets throughout the universe. “Spitzer has given us a better idea of how the raw materials of planets are produced very early on,” said William Forrest of the University of Rochester, N.Y “By studying these other star systems, we can learn about the very beginnings of our own planets 4.6 billion years ago.” The big question is, though, with these crystals, can astronomers foretell the future? (Just kidding)

Planets are born out of swirling pancake-like disks of dust and gas that surround young stars. They start out as mere grains of dust swimming around in a disk of gas and dust, before lumping together to form full-fledged planets. During the early stages of planet development, the dust grains crystallize and adhere together, while the disk itself starts to settle and flatten. This occurs in the first millions of years of a star’s life.

When Forrest and his colleagues used Spitzer to examine five young planet-forming disks about 400 light-years away, they detected the signature of silica crystals. Silica is made of only silicon and oxygen and is the main ingredient in glass. When melted and crystallized, it can make the large hexagonal quartz crystals often sold as mystical tokens. When heated to even higher temperatures, it can also form small crystals like those commonly found around volcanoes.

It is this high-temperature form of silica crystals, specifically cristobalite and tridymite, that Forrest’s team found in planet-forming disks around other stars for the first time. “Cristobalite and tridymite are essentially high-temperature forms of quartz,” said Sargent. “If you heat quartz crystals, you’ll get these compounds.”

In fact, the crystals require temperatures as high as 1,220 Kelvin (about 1,740 degrees Fahrenheit) to form. But young planet-forming disks are only about 100 to 1,000 Kelvin (about minus 280 degrees Fahrenheit to 1,340 Fahrenheit) — too cold to make the crystals. Because the crystals require heating followed by rapid cooling to form, astronomers theorized that shock waves could be the cause.

Shock waves, or supersonic waves of pressure, are thought to be created in planet-forming disks when clouds of gas swirling around at high speeds collide. Some theorists think that shock waves might also accompany the formation of giant planets.

So maybe astronomers will be able to predict the type of planets in this newly forming solar system!

The findings are in agreement with local evidence from our own solar system. Spherical pebbles, called chondrules, found in ancient meteorites that fell to Earth are also thought to have been crystallized by shock waves in our solar system’s young planet-forming disk. In addition, NASA’s Stardust mission found tridymite minerals in comet Wild 2.

Forrest and University of Rochester graduate student Ben Sargent led the research, which will be published in the Astrophysical Journal.

Source: Caltech


Nancy Atkinson is Universe Today's Senior Editor. She also works with Astronomy Cast, and is a NASA/JPL Solar System Ambassador.

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