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News Release 660 of 1051

April 26, 2001 02:00 PM (EDT)

News Release Number: STScI-2001-13

'Survivor' Planets: Astronomers Witness First Steps of Planet Growth - and Destruction

April 26, 2001: Planet formation is a hazardous process. New pictures from the Hubble telescope are giving astronomers the first direct visual evidence for the growth of planetary "building blocks" inside the dusty disks of young WATCH: HubbleMinute Video HubbleMinute: Orion's Survivor Game HubbleMinute: Orion's Survivor Game  stars in the Orion Nebula, a giant "star factory" near Earth. But these snapshots also reveal that the disks are being "blowtorched" by a blistering flood of ultraviolet radiation from the region's brightest star, making planet formation extremely difficult.

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Q & A: Understanding the Discovery

  1. 1. How large are these planetary building blocks?

  2. The building blocks are tiny particles, no larger than snowflakes or pieces of gravel. These small particles have grown 1,000 times in size. Spotting the particles shows that it may be easy to start building planets, even though most may never reach adulthood because of Orion's hostile environment. One astronomer compared the planet-building process in Orion to constructing a skyscraper in the middle of a tornado.

  3. 2. How do astronomers know the sizes of the building blocks?

  4. Astronomers deduced the sizes of the planetary particles by analyzing the colors of light that pass through the disks.

    The fine dust normally seen in space, for example, blocks blue light but allows red light to pass through. The Sun appears red at sunset because atmospheric dust influences light in the same way as space dust.

    The dust disks in Orion, however, process light differently than fine atmospheric dust or space dust. Orion's dust disks appear gray because they allow all colors of light to pass through. This seemingly indiscriminate process is unusual in space and yields clues about the size of the dust in the disks. Astronomers have concluded that the dust is about the size of a snowflake or a piece of gravel, both of which are much larger than space dust.

  5. 3. Can planets form in Orion?

  6. Planets may have a rough time forming in about 90 percent of the young dust disks in Orion. That's because the disks - which started out being billions of miles across - will wither away within 100,000 years, possibly destroying fledgling planets.

    But some astronomers believe that a disk of rocky pebbles may be left behind once the gaseous part of the disk vaporizes away. These rocky disks may be the seeds of terrestrial planets like Earth.

    Although most of Orion's disks will dissipate, about 10 percent may remain intact. That's because these disks may be protected somehow from the destructive ultraviolet radiation. Particles in these disks may continue to accumulate until they become full-fledged planets.

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Credits: NASA, ESA, J. Bally (University of Colorado, Boulder), H. Throop (Southwest Research Institute, Boulder), and C. O'Dell (Vanderbilt University)