British and German astronomers using NASA’s Hubble Space Telescope and telescopes of the W. M. Keck Observatory have detected the remains of an asteroid that contained huge amounts of water circling an old white dwarf star. The discovery suggests that the star had the potential to host Earth-like planets.
This is an artist’s impression of a rocky and water-rich asteroid being torn apart by the strong gravity of the white dwarf star GD 61. Image credit: Mark A. Garlick, Space-art.co.uk / University of Warwick / University of Cambridge.
Dr Jay Farihi from the University of Cambridge’s Institute of Astronomy and his colleagues analyzed the dust and debris surrounding GD 61, a white dwarf located about 163 light-years away from Earth.
They found an excess of oxygen, a chemical signature that indicates that the debris had once been part of a bigger body originally composed of 26 per cent water by mass.
The team suggests it is most likely that the water detected around GD 61 came from a minor planet that once orbited the parent star before it became a white dwarf.
The water was most likely in the form of ice below the planet’s surface. From the amount of rocks and water detected in the outer envelope of the white dwarf, the researchers estimate that the disrupted planetary body had a diameter of at least 90 km.
However, because their observations can only detect what is being accreted in recent history, the estimate of its mass is on the conservative side.
About 200 million years ago, GD 61 entered its death throes and became a white dwarf, yet, parts of its planetary system survived.
The water-rich minor planet was knocked out of its regular orbit and plunged into a very close orbit, where it was shredded by the star’s gravitational force. The astronomers believe that destabilizing the orbit of the minor planet requires a so far unseen, much larger planet going around the white dwarf.
This image shows the white dwarf star GD 61. Image credit: Centre de Données astronomiques de Strasbourg / SIMBAD.
“At this stage in its existence, all that remains of this rocky body is simply dust and debris that has been pulled into the orbit of its dying parent star,” said Prof Boris Gänsicke from the University of Warwick, a co-author of the paper published in the journal Science.
“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 substantial number of similar parent stars,” added lead author Dr Farihi.
“These water-rich building blocks, and the terrestrial planets they build, may in fact be common – a system cannot create things as big as asteroids and avoid building planets, and GD 61 had the ingredients to deliver lots of water to their surfaces.”
“Our results demonstrate that there was definitely potential for habitable planets in this exoplanetary system.”
Astronomers Discover Water-Rich Asteroid Debris Orbiting White Dwarf GD 61
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