First measurement of a day on alien planet

Thursday 1 May 2014

The east side of the Advanced Manufacturing and Design Centre building captured during a sunset.

The European Southern Observatory has announced a world-first measuring a day on exoplanet Beta Pictoris b to be eight hours long. This research may confirm a pattern in the way planets spin in Solar Systems. 

Beta Pictoris b orbits distant star Beta Pictoris, 63 light years from Earth. It is approximately 10 times larger than Jupiter and yet spins at speeds of 100,000km/hr making a day shorter in comparison to that experienced on the much smaller Earth. 

Swinburne University of Technology astronomer Dr Alan Duffy says the finding appears to confirm a pattern seen in our Solar System of larger planets spinning faster and therefore having shorter days than smaller planets, but we still don’t know why this occurs. 

“Beta Pictoris b is the poster-child for exoplanets, being the first directly imaged alien world nearly six years ago. It makes sense that astronomers focussed on this planet to try and determine how fast it’s spinning using one of the largest telescopes in the world, but managing to do this at all is incredibly impressive. 

“Using the same principle as police radar guns, the astronomers were able to measure the Doppler shift in the colour, or wavelength, of the light from the planet. As one side moved towards us it produced a shorter wavelength or bluer colour, and as the other moved away it stretched out the wavelength producing a redder colour. 

“Until today we only knew of the rotations of planets in our own Solar System, with larger planets like Jupiter spinning much more quickly than smaller planets like Earth. We didn’t know if this was something strange with our own Solar System, but with this discovery now we know that it’s seemingly the rule. We just don’t know why. 

“This latest planet is bigger than even Jupiter but with a day just 8 hours long, meaning it’s spinning at a crazy speed 60 times faster than Earth. 

“This planet is young, having formed perhaps only 20 million years ago, meaning it will cool and shrink over time in which case it will spin even faster just as a figure skater spins faster when bringing their arms in. When it shrinks to the width of Jupiter it will have a three hour day,” Dr Duffy said. 

“With the new European-Extremely Large Telescope (E-ELT) under construction we will see more detail, potentially able to get a weather report for this new planet. As Beta Pictoris b is a gas giant it will likely be cloudy.” 

ESO public release information can be found here.