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7 May, 2015
Fresh Evidence for How Water Reached Earth Found in Asteroid Debris
Water delivery via asteroids or comets is likely taking place in many other planetary systems, just as it happened on Earth, according to new research. In work led by Dr Roberto Raddi of the University of Warwick, a team of astronomers find evidence that numerous planetary bodies, including asteroids and comets, contain large amounts of water.
The findings add further support to the possibility that water can be delivered to Earth-like planets via such bodies to create a suitable environment for the formation of life. Commenting on the results, Dr Raddi said: "Our research has found that, rather than being unique, water-rich asteroids similar to those found in our Solar System appear to be commonplace. Accordingly, many planets may contain, or have contained, a volume of water comparable to that found in the Earth. It is believed that the Earth was initially dry, but our research strongly supports the view that the oceans we have today were created as a result of impacts by water-rich comets or asteroids".
Artist's impression of a rocky and water-rich asteroid being torn apart by the strong gravity of the white dwarf star. Similar objects in the Solar System likely delivered the bulk of water on Earth and represent the building blocks of the terrestrial planets. Image copyright Mark A. Garlick, http://space-art.co.uk, University of Warwick [ JPEG ].
In observations obtained at the William Herschel Telescope using ISIS spectrograph, the Warwick astronomers detected a large quantity of hydrogen and oxygen in the atmosphere of a white dwarf (known as SDSS J1242+5226), the compact remnant of a Sun-like star at the end of its life.
This is direct evidence that a water-rich exo-asteroid was disrupted and eventually delivered the water it contained onto the star. This world, the researchers discovered, was comparable in size to Ceres – at 900km across, the largest asteroid in the Solar System.
The impact of water-rich asteroids or comets onto a planet or white dwarf results in the mixing of hydrogen and oxygen into their atmospheres. Both elements were detected in large amounts in SDSS J1242+5226. "The amount of water found in SDSS J1242+5226 is equivalent to 30-35% of the oceans on Earth", explained Dr Raddi.
Research co-author Professor Boris Gänsicke, also of the University of Warwick, explained: "Oxygen, which is a relatively heavy element, will sink deep down into the white dwarf over time, and hence a while after the disruption event is over, it will no longer be visible.
"In contrast, hydrogen is the lightest element; it will always remain floating near the surface of the white dwarf where it can easily be detected. There are many white dwarfs that hold large amounts of hydrogen in their atmospheres, and this new study suggests that this is evidence that water-rich asteroids or comets are common around other stars."
Raddi, R.; Gänsicke, B. T.; Koester, D.; Farihi, J.; Hermes, J. J.; Scaringi, S.; Breedt, E.; Girven, J., 2015, "Likely detection of water-rich asteroid debris in a metal-polluted white dwarf", MNRAS, 450, 2083. Paper.
"Fresh evidence for how water reached earth found in asteroid debris", RAS Press Release, 7th May, 2015.
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