Space and Physics

Planet-Devouring Star Tells Us What Rocky Planets Are Made Of


Dr. Alfredo Carpineti

Senior Staff Writer & Space Correspondent

clockJun 15 2016, 17:32 UTC
An artist's concept illustrating a comet being torn to shreds by a white dwarf star. NASA / JPL-Caltech / T. Pyle (SSC)

A very hungry white dwarf has been gobbling up rocky material from one of its planetoids, and astronomers were able to work out what that material is made of.


Using the Keck Observatory in Mauna Kea, Hawaii, a team of researchers examined the light signals from the star’s atmosphere and discovered that it’s devouring the limestone-encrusted surface of a planet-like body.

“We can see the material that used to make up this planet being accreted and replenished on a daily timescale," said Carl Melis, one of the authors of the research, in a statement. "What we see is what the rock was made of."

White dwarfs are the collapsed core of old stars, burning brightly in a very small volume. The star in the study, called SDSSJ1043+0855, has about the mass of the Sun and a temperature of over 18,000 Kelvin.

The discovery of limestone is definitely intriguing. Its chemical name is calcium carbonate and on Earth it's mostly made of skeleton fragments from dead sea organisms. While this is an indication of a planet rich in carbon, it doesn’t automatically mean that there was once life around this star. 


“In this particular case, the presence of such high levels of carbon is unique and really needs to be explained," continued Melis. "That’s really the hidden subtext."

Calcium carbonate can also be formed in non-biological processes, but the detection implies that finding signatures of life may be dependent on looking at a wider range of parameters.

“When people think about finding extra-terrestrial life, they think about Hollywood dramatizations," said Melis. "But the first evidence of life outside of our Solar System will probably come in a much subtler form. More likely than not, it’s going to come as a nuanced signature that may not be immediately recognizable.”


This observation really provides a new insight into the composition of exoplanets and consequently on how stellar systems form. “It’s a huge issue in exo-planetology right now,” Melis added. “The major exoplanet identifying methods can't tell you what a planet is made of or what its structure is.”

Space and Physics
  • white dwarf,

  • exoplanet,

  • planetary composition