Planets May Take Longer to Form Than Thought

It may take much longer than scientists thought for violent turbulence to turn grains of space dust into new planets.

A NASA telescope recently discovered evidence that the most violent part of the process in forming Earth-sized planets -- the collisions between colossal chunks of rock -- may last hundreds of millions of years instead of 10 million years, scientists at NASA’s Jet Propulsion Laboratory in Pasadena said this week.

Scientists have long believed that planets are formed when the dust in a disk-like formation around a young star begins to clump. Some of the clumps grow to the size of mountains and smash into each other, forming larger embryonic planets.

These, in turn, collide with one another, creating more dust and rocky chunks. In some theories, this brutal stage of planet growth lasts perhaps 10 million years -- an eye blink in astronomical terms.

This is followed by a long, steady, quieter cleanup period in which the unused dust dissipates.

But NASA’s infrared Spitzer Space Telescope revealed that some dust rings around stars remained big and bright even though their stars were 100 million to 200 million years old.

Scientists said the disks couldn’t have survived that long unless violent collisions between embryonic planets and gigantic chunks of rock constantly replenished them.