Evidence for Water in the Rocky Debris of a Disrupted Extrasolar Minor Planet
Remnants of a Water-Bearing World Stars like the Sun end their lives as white dwarfs. Farihi et al. (p. 218) used detailed spectroscopic analysis of a debris-accreting white dwarf, along with knowledge that such systems accrete this debris from remnants of rocky planetary bodies, to derive the water content in a disrupted extrasolar body. The findings suggest that the white dwarf contains the signature of a rocky minor planet composed of 26% water by mass. Spectroscopic analysis of a debris-accreting star in its latest stage of life reveals the remnants of a water-bearing world. The existence of water in extrasolar planetary systems is of great interest because it constrains the potential for habitable planets and life. We have identified a circumstellar disk that resulted from the destruction of a water-rich and rocky extrasolar minor planet. The parent body formed and evolved around a star somewhat more massive than the Sun, and the debris now closely orbits the white dwarf remnant of the star. The stellar atmosphere is polluted with metals accreted from the disk, including oxygen in excess of that expected for oxide minerals, indicating that the parent body was originally composed of 26% water by mass. This finding demonstrates that water-bearing planetesimals exist around A- and F-type stars that end their lives as white dwarfs.