Astronomers have discovered a planet only three times the mass of the Earth – the smallest yet found. It is thought to be a rocky world, like our own, and possibly covered by an ocean.
The new planet is orbiting a tiny sun that shines very dimly and may be a failed star called a brown dwarf.
The world’s discovery is important because it means that similar planets might be circling small, faint stars much closer to the Earth – and life could be common in the universe.
The new planet has no name. It is catalogued only as MOA-2007-BLG-192Lb and lies at a distance of 3,000 light years. Its discovery follows the finding of more than 290 extra solar planets but most of these have been gas giants like Jupiter.
It was discovered using a technique called microlensing, where the stars’s light is magnified by a massive object, such as another star, between it and the telescope.
An international team of astronomers, led by David Bennett, of the University of Notre Dame, Indiana, discovered the new planet. It was first detected using a camera on a telescope at New Zealand’s Mt John Observatory, and confirmed with a bigger instrument, Europe’s Very Large Telescope in Chile.
The planet orbits its host star with an orbital radius similar to that of Venus. But the host is thought to be between three thousand and 1 million times fainter than the Sun, and either a red or a brown dwarf, so the top of the planet’s atmosphere is probably colder than Pluto.
However, the planet is likely to maintain a massive atmosphere that would allow warmer temperatures at lower altitudes. It is even possible that interior heating by radioactive decays would be sufficient to make the surface as warm as the Earth, but theory suggests that the surface may be completely covered by a very deep ocean.
Professor Bennett said: “Our discovery indicates that that even the lowest mass stars can host planets. I’ll hazard a prediction that the first extra-solar Earth-mass planet will be found by microlensing.”
The professor, whose work is partly funded by NASA, announced the discovery at a meeting of the American Astronomical Society in Missouri yesterday. It will be published in September in the Astrophysical Journal.
UK planetary expert Professor John Zarnecki, of the Open University at Milton Keynes, said last night: “The holy grail is to find an planet just like Earth and we are getting closer and closer.
“The environment on a planet like this seems within the limits under which we think life could exist. We don’t have to imagine any fanciful situations – maybe life is more plentiful on worlds like this one than on Earth.”
Professor Zarnecki, who believes life could exist in underground oceans on Saturn’s icy moons Titan and Enceladus, added: “Just a few years ago, planets around other stars were unknown. Now they are almost becoming ten-a-penny. This is where the action is.
“It is a race to see whether we find life first on a remote planet like this or on a world in our own solar system.”
Picture: The image is an artist’s impression of the new planet that assumes the star is a red dwarf. (NASA).