Astronomers have discovered a new Earth-like planet that is larger than our own and may be more than half covered with water, according to a study published Wednesday in the science journal Nature. The so-called super Earth is about 42 light years away in another solar system and has a radius nearly 2.7 times larger than that of our planet, according to the study by the Harvard-Smithsonian Centre for Astrophysics. The discovery of the planet, called GJ 1214b, represents a major step forward in the search for worlds similar to the Earth, added the University of Californias Geoffrey Marcy in a commentary also in Nature. The newfound world is too hot to sustain life as we know it, said the Harvard-Smithsonian Centre for Astrophysics in a statement. Its density suggests however it is composed of about three-fourths water and other ices and one fourth-rock, it said. There are also tantalising hints that the planet has a gaseous atmosphere. Its temperature is estimated at between 280 and 120 degrees Celsius (536 and 248 degrees Fahrenheit) with its host star about one-fifth the size of the Sun, according to the scientists. Despite its hot temperature, this appears to be a waterworld, says Zachory Berta, a graduate student who first spotted hints of the planets presence. It is much smaller, cooler and more Earthlike than any other known exoplanet, he said in the statement. An exoplanet is one outside of our solar system. Berta said some of the water would likely be in crystalline form that exists at pressures greater than 20,000 times Earths sea-level atmosphere. Its temperature is much lower than that on the only similar discovery, called CoRoT-7b, which revolves around a star that is much hotter, the scientists say. The CoRoT-7b has a density close to that of the Earth (5.5 grammes per cubic centimetre) and seems to be rocky, while the new discovery appears to be much less dense (1.9 g/cm3). To keep the planets density that low requires that it contains large amounts of water, said Marcy. It must contain a huge amount of water, roughly 50 percent by mass. The wild card is the make-up of the gases on the planet, he said. The planet orbits every 38 hours around a small, faint star that was first spotted by eight ground-based telescopes no larger than those used by amateur astronomers, the Harvard-Smithsonian Centre said. Its relative closeness makes its possible to study it to determine its atmosphere. That will make it the first super Earth with a confirmed atmosphere-even though that atmosphere probably wont be hospitable to life as we know it, said David Charbonneau who heads the research team. While, scientists once thought that life could originate only within a solar systems habitable zone, where a planet would be neither too hot nor too cold for liquid water to exist on its surface. But according to planetary scientist Francis Nimmo, evidence from recent NASA missions suggests that conditions necessary for life may exist on the icy satellites of Saturn and Jupiter. If these moons are habitable, it changes the whole idea of the habitable zone, said Nimmo, a professor of Earth and planetary sciences at UC Santa Cruz. AFP/SD It changes our thinking about how and where we might find life outside of the solar system. Nimmo discussed the impact of ice dynamics on the habitability of the moons of Saturn and Jupiter on Tuesday at the annual meeting of the American Geophysical Union in San Francisco. Jupiters moon Europa and Saturns moon Enceladus, in particular, have attracted attention because of evidence that oceans of liquid water may lie beneath their icy surfaces. This evidence, plus discoveries of deep-sea hydrothermal vent communities on Earth, suggests to some that these frozen moons just might harbour life. Liquid water is the one requirement for life that everyone can agree on, Nimmo said. The icy surfaces may insulate deep oceans, shift and fracture like tectonic plates, and mediate the flow of material and energy between the moons and space. Several lines of evidence support the presence of subsurface oceans on Europa and Enceladus, Nimmo said. In 2000, for example, NASAs Galileo spacecraft measured an unusual magnetic field around Europa that was attributed to the presence of an ocean beneath the moons surface. On Enceladus, the Cassini spacecraft discovered geysers shooting ice crystals a hundred miles above the surface, which also suggests at least pockets of subsurface water, Nimmo said. Liquid water isnt easy to find in the cold expanses beyond Earths orbit. But according to Nimmo, tidal forces could keep subsurface oceans from freezing up. Europa and Enceladus both have eccentric orbits that bring them alternately close to and then far away from their respective planets. These elongated orbits create ebbs and flows of gravitational energy between the planets and their satellites. A moon like Enceladus is getting squeezed and stretched and squeezed and stretched, Nimmo said. The extent to which this squeezing and stretching transforms into heat remains unclear, he said. Tidal forces likely shift plates in the lunar cores, creating friction and geothermal energy. This energy may also rub surface ice against itself at the sites of deep ice fissures, creating heat and melting, according to Nimmo. Enceladuss geysers appear to originate from these shifting faults, and the thin lines running along Europas surface suggest geologically active plates, he said. A frozen outer layer may be crucial to maintaining oceans that could harbour life on these moons. The icy surfaces may shield the oceans from the frigidity of space and from radiation harmful to living organisms. If you want to have life, you want the ocean to last a long time, Nimmo said. The ice above acts like an insulating blanket. Enceladus is so small and its ice so thin that scientists expect its oceans to freeze periodically, making habitability less likely, Nimmo said. Europa, however, is the perfect size to heat its oceans efficiently. It is larger than Enceladus but smaller than moons such as Ganymede, which has thick ice surrounding its core and blocking communication with the exterior. If liquid water exists on Ganymede, it may be trapped between layers of ice that separate it from both the core and the surface. SD The core and the surface of these moons are both potential sources of the chemical building blocks needed for life. Solar radiation and comet impacts leave a chemical film on the surfaces. To sustain living organisms, these chemicals would have to migrate to the subsurface oceans, and this can occur periodically around ice fissures on moons with relatively thin ice shells like Europa and Enceladus. Organic molecules and minerals may also stream out of their cores, Nimmo said. These nutrients could support communities like those seen around hydrothermal vents on Earth. Nimmo cautioned that being habitable is no guarantee that a planetary body is actually inhabited. It is unlikely that we will find life elsewhere in our solar system, despite all the time and resources devoted to the search, he said. But such a discovery would certainly be worth the effort. I think pretty much everyone can agree that finding life anywhere else in the solar system would be the scientific discovery of the millennium, Nimmo said. SD