Do Not Cross This Line

April 23, 2007 — Leave a comment

Rosette Nebula Spitzer

NASA researchers using the Spitzer space telescope have laid out what they have called ‘planetary danger zones’ around stars. In these zones, extending from bright O-stars, protoplanetary disks will be swept away by the strong stellar winds given out by the star. Smaller,cooler stars will continue forming planets from accretion disks so long as they remain at least 1.6 light years (10 trillion miles) from any nearby O stars.

Planets form in dusty accretion disks around stars but the powerful O and B type stars bellow out ultra viloet radiation too powerful to allow these disks to remain in tact. They are swept up by the radiation and the protoplanets inside never form. So long as they remain outside any such danger zones, it seems these planets will survive.

The team at NASA surveryed the Rosette Nebula over 5,200 lights years away in the contellation Monoceros. This is a star forming region and a well studied object in the sky. They used Spitzer to observe over 1,000 stars in the vicinty of an O type star and found that only 27 percent of those sytems within 1.6 light years had any kind of disk compared to 45 percent outisde of this danger zone. The image at the top shows the nebula and five of the O stars with their danger zones highlighted.

Stars are not static and do move around, especially within the timescales of planet formation. This study helps scientists to start to pin down the possible speed of planet formation. It could be thet Jupiter-like planets form quickly and would be able to withstand the motion of its parents star toward one these danger zones. Earth-type planets are thought to take longer to form however and would not survive even a brief foray inside sich a barrier.

It is thought that our Sun, like most stars, formed in a group which would have included such powerful O stars. If so then this means the Sun must have migrated out of the group before the planets we are familar with formed. For more on this story check out NASA’s press release.

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