Planetary Ingredients All Mixed Up
By Govert Schilling
ScienceNOW Daily News
17 April 2007

PRESTON, U.K.--Planets are born from hardscrabble roots, including gases left over from the early days of the universe and dust shed from dying stars. Now astronomers have observed how a traveling star mixes up these ingredients with eddies and shock waves. The finding--presented here today at the Royal Astronomical Society National Astronomy Meeting--verifies a recent computer model and provides insights that could give a deeper understanding of the interstellar processes that give rise to planets--and the kind of complex molecules that have led to life.
The dusty building materials come from sun-like stars that expand into bloated red giants at the end of their lives. Their outer layers slowly drift off into space, carrying elements such as carbon that are vital to the origin of life. At a later stage, the stellar ashes become visible as a planetary nebula, a hot blob of gas rich in oxygen, carbon, and nitrogen. Although astronomers knew that these materials were eventually mixed and distributed through space, it wasn't exactly clear how that happened. Last year, supercomputer simulations by astronomer Chris Wareing of Jodrell Bank Observatory in the U.K. and colleagues revealed whirlpools and a type of turbulence called bow shock in the nebula, depending on the star's speed. Now, they claim to have observed these effects in a planetary nebula known as Sharpless 2-188.

Sharpless 2-188 is 850 light-years away in the constellation Cassiopeia. Unlike many planetary nebulae, it's lopsided instead of spherical. According to Wareing's team, the brightest part of the nebula corresponds to bow shock in the ejected material, resulting from the star's motion of 125 kilometers per second. Images obtained by another group with the 2.5-meter Isaac Newton Telescope on La Palma, Canary Islands, also show vortices in the extremely faint "downstream" part of the nebula, matching the computer simulations.

"It's an exciting find," says astrophysicist Ciska Markwick-Kemper of the University of Manchester in the U.K. "We need these kind of details in order to understand the survival rates of dust particles and complex molecules." These features should eventually help clarify how stellar material is recycled into new planets and the role of turbulence in creating dense zones of material where complex molecules could persist.