December 9, 2004: Two of NASA's Great Observatories, the Spitzer Space Telescope and the Hubble Space Telescope, have provided astronomers an unprecedented look at dusty planetary debris around stars the size of our sun. Spitzer has discovered for the first time dusty discs around mature, sun-like stars known to have planets. Hubble captured the most detailed image ever of a brighter disc circling a much younger sun-like star. The findings offer "snapshots" of the process by which our own solar system evolved, from its dusty and chaotic beginnings to its more settled present-day state.
Debris disks are composed of the shattered remnants of small bodies such as comets and asteroids that collided as they orbited the star. A similar, though much less dense cloud of dust orbits our Sun. Large, gaseous planets like Jupiter might already exist in such systems, while much smaller rocky planets like the Earth may be just starting to form.See the rest:
When a star forms through the collapse of a huge cloud of gas and dust, some of the material will settle into a flattened disk around the star that is at a right angle to the star's spin axis. This material has maximum centripetal force along this plane and so resists falling into the star. The disk eventually dissipates after the star ignites. But before it does, planets, asteroids, and comets may agglomerate from dust sticking together in the disk. A secondary disk forms when the smaller bodies collide and grind each other back down to dust.
NASA's Spitzer Space Telescope has detected the telltale infrared glow of excess dust around a number of young stars. However, some stars appear to lose material too early to make planets. What's new is that some of the stars with debris disks have planets, as identified in previous studies. These planets have never been directly seen but identified through the telltale gravitational wobble they induce on the star. The new Spitzer observations are the first direct link between existing extrasolar planets and circumstellar disks.
Secondary disks around young stars are very dusty due to a spate of violent collisions. Our solar system is somewhat middle-aged, and the rate of collisions has died down dramatically. Still, the ecliptic plane of our solar system, where all the major planets and asteroids lie, has about one ten-thousandth as much dust as seen around young stars. This can be seen from Earth as a thin pillar of faint light in the night sky called the Zodiacal Light. It is best seen from the tropics where the ecliptic is typically at a steep vertical angle to the horizon.