Astronomers have found the first Earth-sized exoplanet three thousand light years away. The planet was discovered by the science-fiction-sounding method of gravitational microlensing, and shows that there might be far more planets out there than we ever suspected.
The planet is three times the size of Earth, which might sound like a fairly significant difference but you have to remember that in astronomical terms even being within a factor of ten is an amazing similarity. Every other exoplanet yet discovered has been much larger, many times the size of our own solar system's heavyweight gas giant Jupiter. This is more to do with the sensitivity of our measurements than the makeup of the universe, however, which is where new tools and methods like the Microlensing Observations in Astrophysics (MOA) telescope-camera based in New Zealand come in.
Gravitational lensing was first used as a proof of general relativity, the idea that a massive object like a star bent space and light around it. If two stars and the Earth are in precise alignment, the middle star will bend the light from the further star towards Earth, making it appear brighter than it otherwise would - that is to say, 'lensing' it. Microlensing studies examine these images even more carefully and can reveal planets orbiting the lens star from minute variations in the focused light.
That's exactly how the international team of scientists discovered the Earth-scale exoplanet, which you'd really think they'd give a snappier name than MOA-2007-BLG-192Lb. It's also interesting because of the star it orbits - which almost isn't a star at all. At 6-8% of the sun's mass it's tiny, far smaller than any star previously observed to host planets. There is debate as to whether it can even support fusion reactions, or whether it's a "brown dwarf" - a failed coulda-been star that never sparked into nuclear light and is now slowly trading internal energy for heat until it runs out and goes cold.
This great success in planetary survey techniques raises hopes for the discovery of many, many more planets - not only do we have an accurate and convincingly demonstrated technology, but it seems we have many more places to point it as well.
Posted by Luke McKinney.