Saturday, October 12, 2013

Astronomers: Dying solar system once harbored vast amounts of water

Astronomers: Dying solar system once harbored vast amounts of water

Approximately 150 light years away lies the star GD 61, a white dwarf nearing the end of its life. GD 61 was once three times more massive than our Sun. Once the star had used up its supply of hydrogen, it began fusing helium into carbon and swelled into a red giant. However, GD 61 lacked sufficient mass to begin fusing carbon, allowing carbon and oxygen to build up in its center. Eventually, the dying star shed its outer layers, leaving an exceptionally dense stellar remnant with a mass comparable to our Sun but with a volume comparable to that of Earth.
A new study led by Jay Farihi of the University of Cambridge has discovered a fragmented dwarf planet around GD 61. Unlike the more than 900 exoplanets discovered around younger stars, the broken dwarf planet orbiting GD 61 has been shattered by the intense gravity of the white dwarf, allowing scientists to study its composition. Debris from the planet has been drawn close to GD 61, and so the team used ultraviolet measurements from the Cosmic Origins Spectrograph on the Hubble Space Telescope to determine the amount of oxygen present in the atmosphere of the white dwarf star.
The ultraviolet measurements allowed the researchers to detect the abundances of magnesium, silicon, iron, and other elements in the contaminated atmosphere of the star. This allowed them to predict how much oxygen should be present in the atmosphere of the star. Farihi and team found significantly more oxygen than they expected. The team ruled out comets as a source of the oxygen because comets, in addition to carrying oxygen in water molecules, also bear large amounts of carbon, and the atmosphere of GD 61 is devoid of carbon. This means that the excess oxygen was probably delivered in water molecules contained within the shattered dwarf planet.
So rich in water was the fragmented dwarf planet that water accounted for 26% of its mass, similar to Ceres, a dwarf planet and the largest object in our solar system’s asteroid belt. By comparison, the blue planet Earth is only 0.02% water mass; indeed, most of the water on Earth was probably delivered by water-rich asteroids early in the planet’s history.
The discovery of a water-rich body in the GD 61 star system provides a glimpse ahead at what our solar system will be like in six billion years, as our own Sun nears the end of its life. It also suggests that habitable planets might have once existed around GD 61. “The finding of water in a large asteroid means the building blocks of habitable planets existed – and maybe still exist – in the GD 61 system, and likely also around a substantial number of similar parent stars,” Farihi explained in a University of Cambridge press release.
The existence of a shattered dwarf planet in the GD 61 system also suggests the presence of one or more gas giants, the gravity of which would have pushed the dwarf planet and other water-rich bodies closer to the white dwarf star. As they moved closer to GD 61, the star’s gravity tore them apart, giving Farihi and colleagues their unique look inside an object in another solar system.
The new study was published in the October 11 issue of the journal Science.

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