[meteorite-list] NASA's Hubble Space Telescope Finds Dead Stars 'Polluted' With Planet Debris

[Ron Baalke]

May 09, 2013

J.D. Harrington 
Headquarters, Washington 
202-358-5241 
j.d.harrington at nasa.gov 

Ray Villard 
Space Telescope Science Institute, Baltimore, Md. 
410-338-4514 
villard at stsci.edu 


RELEASE: 13-133

NASA'S HUBBLE SPACE TELESCOPE FINDS DEAD STARS 'POLLUTED' WITH PLANET DEBRIS

WASHINGTON -- NASA's Hubble Space Telescope has found the building 
blocks for Earth-sized planets in an unlikely place-- the atmospheres 
of a pair of burned-out stars called white dwarfs. 

These dead stars are located 150 light-years from Earth in a 
relatively young star cluster, Hyades, in the constellation Taurus. 
The star cluster is only 625 million years old. The white dwarfs are 
being polluted by asteroid-like debris falling onto them. 

Hubble's Cosmic Origins Spectrograph observed silicon and only low 
levels of carbon in the white dwarfs' atmospheres. Silicon is a major 
ingredient of the rocky material that constitutes Earth and other 
solid planets in our solar system. Carbon, which helps determine 
properties and origin of planetary debris, generally is depleted or 
absent in rocky, Earth-like material. 

"We have identified chemical evidence for the building blocks of rocky 
planets," said Jay Farihi of the University of Cambridge in England. 
He is lead author of a new study appearing in the Monthly Notices of 
the Royal Astronomical Society. "When these stars were born, they 
built planets, and there's a good chance they currently retain some 
of them. The material we are seeing is evidence of this. The debris 
is at least as rocky as the most primitive terrestrial bodies in our 
solar system." 

This discovery suggests rocky planet assembly is common around stars, 
and it offers insight into what will happen in our own solar system 
when our sun burns out 5 billion years from now. 

Farihi's research suggests asteroids less than 100 miles (160 
kilometers) wide probably were torn apart by the white dwarfs' strong 
gravitational forces. Asteroids are thought to consist of the same 
materials that form terrestrial planets, and seeing evidence of 
asteroids points to the possibility of Earth-sized planets in the 
same system. 

The pulverized material may have been pulled into a ring around the 
stars and eventually funneled onto the dead stars. The silicon may 
have come from asteroids that were shredded by the white dwarfs' 
gravity when they veered too close to the dead stars. 

"It's difficult to imagine another mechanism than gravity that causes 
material to get close enough to rain down onto the star," Farihi 
said. 
By the same token, when our sun burns out, the balance of 
gravitational forces between the sun and Jupiter will change, 
disrupting the main asteroid belt. Asteroids that veer too close to 
the sun will be broken up, and the debris could be pulled into a ring 
around the dead sun. 

According to Farihi, using Hubble to analyze the atmospheres of white 
dwarfs is the best method for finding the signatures of solid planet 
chemistry and determining their composition. 

"Normally, white dwarfs are like blank pieces of paper, containing 
only the light elements hydrogen and helium,"Farihi said. "Heavy 
elements like silicon and carbon sink to the core. The one thing the 
white dwarf pollution technique gives us that we just won't get with 
any other planet-detection technique is the chemistry of solid 
planets." 

The two "polluted" Hyades white dwarfs are part of the team's search 
of planetary debris around more than 100 white dwarfs, led by Boris 
Gansicke of the University of Warwick in England. Team member Detlev 
Koester of the University of Kiel in Germany is using sophisticated 
computer models of white dwarf atmospheres to determine the 
abundances of various elements that can be traced to planets in the 
Hubble spectrograph data. 

Farihi's team plans to analyze more white dwarfs using the same 
technique to identify not only the rocks' composition, but also their 
parent bodies. 

For more information about NASA's Hubble Space Telescope, visit: 

http://www.nasa.gov/hubble 
	
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