GD 61

GD 61 is a white dwarf star. It is 150 light-years from Earth in the constellation Perseus.
 The star has a planetary system. It may once have been a main sequence star of spectral type A0V with around three times the mass of the Sun. It has aged and passed through a red giant phase. What was left is a dense hot remnant. This remnant has around 70% of the Sun's mass and a surface temperature of 17280 K. It is thought to be around 600 million years old. This age includes both its life as a main sequence star, and as a white dwarf stellar remnant. It has an apparent magnitude of 14.8. GD 61 was first noted as a potential degenerate star in 1965. This was done in a survey of white dwarf suspects by astronomers from the Lowell Observatory in Arizona.
An asteroid in the system was detected in 2013 that contains water. This was the first finding of solid or liquid water on an extrasolar body. The asteroid, the first extrasolar asteroid detected, is 26% water by mass, close to the water content of Ceres. This means that a planet, with a rocky surface similar to Earth's, may have existed in the past. The asteroid could be an artifact from this period. It is now possibly part of a debris field from that planet's breakup. Such a planet would have had both a rocky surface and water. These are two key ingredients for life. The researchers used the Cosmic Origins Spectrograph on the Hubble Space Telescope to determine what it is made of. The elements magnesium, silicon, iron and oxygen were detected. These are all components of rocky planets. However, the amount of oxygen is much higher than what was expected. There was also less carbon than expected. This meant there was one possible reason for the extra oxygen. There had to be water there.