14.07 light-years away
Van Maanen's Star
What does the nearest dead star tell us about what happens to planets?
Fourteen light-years away sits the ember of a star that finished burning long ago. Its atmosphere should be pure hydrogen and helium. It is not, and that discrepancy is the point.
The nearest star that is over
Adriaan van Maanen found it in 1917. It is a white dwarf: the exposed core of a star that ran out of fuel, shed its outer layers and now simply cools, with roughly the Sun's mass compressed into an Earth-sized sphere. It is the nearest such object that is not orbiting a companion, which makes it the cleanest nearby example of a stellar afterlife.
The metals that should not be there
A white dwarf's gravity is so fierce that anything heavier than helium sinks out of sight within days or years — geologically no time at all. So heavy elements in the atmosphere of an old white dwarf cannot be left over from its youth. They must have arrived recently.
Van Maanen's Star has them, and it was among the first where this was noticed. The explanation now accepted is that it is accreting debris: asteroids or fragments of planets, torn apart and pulled in. Studying that debris tells us what those bodies were made of, which makes a dead star one of the few places we can measure the composition of rocky worlds outside the solar system.