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This page was published on 05/06/2007
Published: 05/06/2007


Published: 5 June 2007  
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Astronomers discover water planet before a star

Good news for astronomers the world over. A team of European astronomers has successfully measured the transit of a Neptune-sized planet around another star. The team, headed by researcher Michaël Gillon from the University of Liège, remarked that measuring the size and density of such an extra-solar planet has provided evidence that the planet, which has a diameter of about 50 000 km – quadruple to that of the Earth's, is made up mostly of water. They added that the level of hydrogen and helium would affect the actual size of the planet.

The extra-solar planet is four times bigger than Earth. © Matt+
The extra-solar planet is four times bigger than Earth.
The star GJ 436 is small and 30 light-years from the Sun. For the last three years, researchers have known that it has been harbouring a 22-Earth mass planet, orbiting 4 million kilometres (0.03 Astronomical Units) from the star. Initial studies from the Swiss-based OFXB observatory have pointed to a periodic dimming of the star, brought on by the passage of the planet in front of it. The Wise Observatory in Israel later confirmed this event, which the experts call a 'transit', and astronomers at the Geneva University Observatory in Chile later measured it with the Euler telescope.

Concerning a planet's size and mass, it would be like the planet Jupiter or Saturn if it were composed of mostly hydrogen and helium, or it would be as small as Earth or Venus if it was made up of rock and iron, the researchers remarked.

The proximity of the planet and its host star, according to the research team, would likely make its surface reach a temperature of at least 300°C. Consequently, the water found in an environment with this temperature would be in steam form. Intense pressure crushes the water, which then assumes a state that can only be identified in a laboratory.

‘Water has more than a dozen solid states, only one of which is our familiar ice,’ explained Frédéric Pont, a member of Dr Gillon's research team. ‘Under very high pressure, water turns into other solid states denser than both ice and liquid water, just as carbon transforms into diamond under extreme pressures,’ he added. ‘Physicists call these exotic forms of water “Ice VII” and “Ice X”. If Earth's oceans were much deeper, there would be such exotic forms of solid water at the bottom.’ The ice inside GJ 436's planet is heated to several hundred degrees, the researchers said.

This latest discovery helps astronomers further understand planets and their proximity to their stars, as well as how planets of similar mass detected around other stars, may be made up mainly of water.

‘This discovery is an important step towards the detection and study of Earth-like planets,’ said Dr Gillon in a statement.

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European Space Policy on Europa
University of Liège

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