NASA's Kepler discovers a wobbly world

Exoplanet Kepler-413b is very unstable on its spin axis


Credit: NASA, ESA, and A. Feild (STScI)

This illustration shows the unusual orbit of Kepler-413b around a close pair of stars

The UK’s seasonal weather has been difficult to predict over the past few years – wet summers, windy winters – but it appears NASA’s Kepler Space Telescope may have discovered a planet where the weather is even more erratic. A strange, unsteady world that wobbles violently on its spin axis.

The tilt of Kepler-413b’s axis can vary by as much as 30 degrees over an 11-year period. In comparison, Earth's rotational precession (wobble) is just 23.5 degrees over 26,000 years. This means the climate on Kepler-413b is very interchangeable Indeed.

As well as wobbling on its own axis, Kepler 413-b has an unstable orbit around its parent stars – a pair of orange and red dwarfs. This is because the planet’s orbital plane is misaligned to that of the star pair’s.

Astronomers operating Kepler are used to spotting planets with regular transits, but when observing Kepler-413b they discovered something very different.

Veselin Kostov was the principal investigator on the observation, "Looking at the Kepler data over the course of 1,500 days, we saw three transits in the first 180 days, one transit every 66 days , then we had 800 days with no transits at all. After that, we saw five more transits in a row.”

Scientists are still unable to explain why the odd planet is so out of synch with its stars, but they do have a few theories. The bizarre orbit could be down to the effect of other planetary bodies. Or the gravitational force of a third star could be pulling the planet out of its regular orbit.


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