IMAGE: Remnants of planetary crust disintegrating under the tidal forces around a cool white dwarf. Material in the disc becomes vaporised close to the central star and flows onto the white dwarf atmosphere. CREDIT: University of Warwick/Mark Garlick
It turns out that we can actually measure the amount of planetary debris in the outer layers of white dwarf stars.
In a new paper published in Nature Astronomy, astronomers from the University of Warwick report on findings from observations of white dwarfs using data from the Gaia telescope. First, they found one unusual signal in the spectroscopic data, which they were using to analyze the composition of the outer layers. The signal turned out to be lithium, and as we have repeatedly mentioned, when you find one example, there are likely more out there. So they dug through the data and found three more white dwarfs with a lithium signal. And found one of those white dwarfs had potassium as well.
The team then compared the amounts of lithium and potassium they found with the amounts of sodium and calcium observed. All of these comparisons led to the conclusion that the chemical composition matched the crusts of rocky planets like Earth ...