For when I get my spaceship

Watery, rocky planets may be common in the Milky Way. That is all.

White dwarf stars are the endpoint of stellar evolution for the vast majority (>90%) of all stars in the Milky Way, including our Sun. Because they should have essentially pure hydrogen or pure helium atmospheres, if heavier elements are found then these must be external pollutants.

Instead, rocky planetary debris is almost certainly the culprit in most or all cases.

The new work indicates that at least 3% and perhaps as much as 20% of all white dwarfs are contaminated in this way, with the debris most likely in the form of rocky minor planets with a total mass of about that of a 140 km diameter asteroid.