What unreliable neighbours we have. Last year astronomers announced the discovery of a planet with a similar mass to Earth's just 4.3 light years away in the nearby Alpha Centauri system. Another look suggests the planet may not be there after all.
Xavier Dumusque of the Geneva Observatory in Switzerland and colleagues identified the planet, known as Alpha Centauri Bb, from around 450 observations of Alpha Centauri B, the smaller of the two stars in the system.
The team looked for changes in the star's light that could be caused by an orbiting planet, whose gravitational tug would induce a slight wobble in the star. This method, known as radial velocity, is often successfully used to hunt exoplanets. But smaller planets have less of a gravitational tug, so finding such worlds in this way is more difficult. That is because noise from the star can obscure the subtle signal and so must be carefully filtered out.
Dumusque filtered the data by removing any periodic signals, such as dark sunspots, that synced up with the rotation of the star. The remaining signal was interpreted as an orbiting planet.
But Artie Hatzes of the Friedrich Schiller University in Jena, Germany, begs to differ. After using two alternative filters, he says Bb might not exist after all. "I don't say it is not there, but I cast serious doubt," he says.
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