Image: Star with disk
M. Weiss  /  CXC
In this illustration, large flares loop out from a young star. X-rays from the flares heat up the planet-forming disk of gas and dust surrounding the star and give it an electric charge. The energy creates turbulence in the disk, knocking around Earthlike planets (like the one in blue) — and keeping them from migrating inward rapidly.
By Senior science writer
updated 5/10/2005 2:00:27 PM ET 2005-05-10T18:00:27

The sun might have had an incredibly violent youth in which tremendous X-ray flares battered Earth into being, a new star survey suggests.

In examining 30 very young sunlike stars, astronomers found that some were relatively calm while others kicked up flares that were vastly more powerful than anything the sun generates today.

Astronomers are not overly surprised to find that stars were more active in their youth, but the results suggest a non-intuitive outcome.

While one might assume a violent beginning wouldn't favor the development of planets, just the opposite might be true, according to one theory. The reasoning goes like this: Intense flares might keep developing planets at bay, whereas without the flares a rocky world might tumble in and be vaporized by a newborn star.

Planet birth
Rocky planets like Earth are thought to form in the first few million years after a star is born. Dust orbits a newborn star in a flat disk. Some of the dust sticks to make asteroidlike objects. These often collide and are destroyed, but some come together more gently, and planets are born.

Image: Orion Nebula Cluster
NASA / CXC / Penn State
This is a deep image of the Orion Nebula Cluster made by the Chandra X-ray Observatory. The luminous source in the middle, Theta Orion Nebulais C, is the cluster's brightest and most massive star.
One theory holds that X-ray flares would heat a planet-forming disk and give it an electric charge. The charge, combined with the disk's motion and magnetic fields, would create turbulence. The turbulence would knock planets in and out, "something like boats tossed about by waves on a storm," astronomer Joan Najita of the National Optical Astronomy Observatory explained.

Overall, the effect would prevent a planet's tendency otherwise to migrate rapidly inward, Najita said in a teleconference with reporters Tuesday.

The new observations, by NASA's Chandra X-ray Observatory, found that flares on some sunlike stars are 100 times more powerful than on others. On the average star in the survey, a flare more powerful than modern solar flares occurs once a week.

About half the stars in the survey, in the Orion star-forming region about 1,500 light-years away, show evidence for harboring disks from which planets might form.

"We don't have a time machine to see how the young sun behaved, but the next best thing is to observe sunlike stars in Orion," said Scott Wolk of the Harvard-Smithsonian Center for Astrophysics. "We are getting a unique look at stars between 1 [million] and 10 million years old — a time when planets form."

What about us?
Theorists don't know where the sun formed. It might have been born in isolation, collapsing from a cloud of interstellar gas and dust. Most stars form in dense regions like Orion, however.

The sun might have formed in an Orionlike environment, only to be booted out to its present, lonely position, according to one theory. Such a chaotic beginning might explain why Uranus and Neptune are largely blocks of ice; perhaps their outer gaseous envelopes were stripped by radiation from stars that were once nearby, the thinking goes.

"Big X-ray flares could lead to planetary systems like ours where Earth is a safe distance from the sun," said Eric Feigelson of Penn State University, principal investigator for the international Chandra Orion Ultradeep Project. "Stars with smaller flares, on the other hand, might end up with Earthlike planets plummeting into the star."

The astronomers pointed out that while solar flares today are seen as threatening to satellites and even cause radiation concerns for people in aircraft, the more powerful flares that might have occurred early in our sun's history helped create a world where life would later form.

The scope of the early chaos is staggering: Hundreds of millions of powerful flares would spew out from a young star during the time it takes for an Earthlike planet to form.

No Earth-sized planets have been found around other stars, but technology hasn't matured enough to detect anything so small. Astronomers expect to find several rocky planets later this decade with new space-based telescopes.

An artist's animation of a typical flare can be seen here.

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