An artist’s impression of a planetary fragment orbiting the star SDSS J122859.93+104032.9, leaving a tail of gas in its wake. University of Warwick/Mark Garlick
Could this be the eventual fate of Earth? Astronomers have discovered a grisly scene of planetary destruction, with a fragment of a planet being all that is left circling the dark remains of a dead star.
The dead star, located 400 light-years away from Earth, is called SDSS J122859.93+104032.9 and has suffered a cataclysmic collapse. Astronomers from the University of Warwick, U.K., were looking at the white dwarf and were surprised to see a fragment orbiting it, which they believe is the remains of a planet.
The fact that anything remains of the planet at all is remarkable, as it sits close enough to its star to orbit every two hours. This is “much closer to [the star] than we would expect to find anything still alive,” according to Professor Boris Gaensicke, co-author of the paper from the Department of Physics at University of Warwick, describing the planet fragment as being located “deep into the gravitational well of the white dwarf.”
A white dwarf is the core that remains after a star burns off all its fuel and dies. They are very dense, with a mass similar to our Sun squeezed into a space about the size of our Earth. They do give off faint luminosity, but not because of fusion like live stars — rather, because they emit stored thermal energy.
The team thinks the tough little planetary fragment must be very dense or have considerable internal strength to have survived so close to a white dwarf, which is why they believe it is made of metals like iron and nickel. They calculate that the planet was originally at least a kilometer (0.6 miles) in size and could have been up to a few hundred kilometers (more than 100 miles) across, making it comparable to the largest asteroid that we see in our Solar System.
When our Sun dies, however, we won’t have to worry about our planet being ripped apart by gravity. It will be disintegrated by the expansion of the Sun long before that happens.
“As stars age they grow into red giants, which ‘clean out’ much of the inner part of their planetary system,” Dr Christopher Manser, a Research Fellow in the Department of Physics, said. “In our Solar System, the Sun will expand up to where the Earth currently orbits, and will wipe out Earth, Mercury, and Venus. Mars and beyond will survive and will move further out. The general consensus is that 5-6 billion years from now, our Solar System will be a white dwarf in place of the Sun, orbited by Mars, Jupiter, Saturn, the outer planets, as well as asteroids and comets.”
The findings are published in Science.
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