NASA: Making Planets Takes Time

It may take much longer than scientists have 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 an Earth-sized planet — the collisions between colossal chunks of rock — may last hundreds of millions of years instead of 10 million years, scientists said Monday at NASA's Jet Propulsion Laboratory in Pasadena, California.

Scientists have long believed that planets are formed when the dust in a disc-like formation around a young star begins to clump. Some of the clumps eventually 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 or so — an eye blink in astronomical terms.

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

But the new findings indicate the violent phase may last much longer.

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 discs couldn't have survived that long unless violent collisions between embryonic planets and gigantic chunks of rock were constantly replenishing them.

"Now we will have to rewrite the textbooks. ... The discs can last much longer than previously thought," said Jonathan Gardner, a Spitzer program scientist in Washington, D.C.

By Robert Jablon