A planet orbiting a nearby star is a water world, according to new research from a team of European astronomers which is published in the journal Astronomy and Astrophysics. The planet was first discovered in 2004, orbiting a red dwarf star called GJ436, which is some 30 light years from the Sun. Its mass is 22 times that of the Earth and it orbits its star every 2.6 days at a distance of 4 million km. Now, Belgian, Swiss and Israeli astronomers have been able to measure the planet, thanks to measurements taken using the Euler telescope operated by the Geneva University located at La Silla Observatory in Chile. The planet's diameter is 50,000 km; four times that of the Earth. Knowing the planet's size and mass, the researchers were able to infer that it is mainly composed of water. If it was made of hydrogen and helium, like Jupiter, it would be larger, while if it were a rocky planet like Earth it would be smaller. So what does this water world look like? According to the researchers, the world could be surrounded by an envelope of hydrogen and helium, like Neptune and Uranus, or surrounded by water, like many of Jupiter's moons. Due to its close proximity to the sun, the surface of the planet is likely to be extremely hot, with a temperature of 300°C, meaning that any water present in the atmosphere would be in the form of steam. Inside the planet, the water will be crushed into a solid under intense pressure. However, this solid water will not be ice. 'Water has more than a dozen solid states, only one of which is our familiar ice,' explains Frédéric Pont, of Geneva University, one of the authors of the paper. '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.' These exotic forms of water are called Ice VII and Ice X, and inside the planet under study, they are heated to many hundreds of degrees. 'This discovery is an important step towards the detection and study of Earth-like planets,' commented lead researcher Michaël Gillon of the University of Liège.
Belgium, Switzerland, Israel