Author: Daniel Clery / Source: Science | AAAS
In a glimpse of what may be in store for our own solar system, astronomers have discovered what appear to be the shattered remains of a planet orbiting a white dwarf, the burned-out ember of a star like our sun.
If the team’s calculations are correct, the orbiting object may be the iron core of a small planet that had its outer layers ripped off by the white dwarf’s intense gravity.Although astronomers know of thousands of exoplanets in the Milky Way, they struggle to see anything much smaller than Earth. The new object is by far the smallest, more of an asteroid than a planet. Its discovery also provides a clue into the fate of planets as their stars age. When sunlike stars run out of hydrogen fuel and start to burn elements like helium and carbon, they swell up into red giants and consume any planets that orbit too close. Those that survive witness what can happen next when the red giant’s fuel is exhausted: It collapses into a small and dense white dwarf, which cools over trillions of years. Its intense gravity can rip apart any surviving planets that stray too close, consuming some material and leaving the rest in a swirling disk of dust.
Finding the planetesimal, 400 light-years from Earth, wasn’t easy. A team of astronomers, led by Christopher Manser of the University of Warwick in Coventry, U.K., had been watching this particular white dwarf for 15 years. They gained some observing time on the world’s largest optical telescope, the 10.4-meter Gran Telescopio Canarias on La Palma in Spain’s Canary Islands, in 2017 and 2018. The white dwarf, known as SDSS J122859.93+104032.9, or SDSS J1228+1040 to its friends, is one of only a handful of white dwarfs with a surrounding disk of both gas and debris, and the team wanted to study minute-by-minute changes in the gas.
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