Letter | Published:

Fast spin of the young extrasolar planet β Pictoris b

Nature volume 509, pages 6365 (01 May 2014) | Download Citation

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Abstract

The spin of a planet arises from the accretion of angular momentum during its formation1,2,3, but the details of this process are still unclear. In the Solar System, the equatorial rotation velocities and, consequently, spin angular momenta of most of the planets increase with planetary mass4; the exceptions to this trend are Mercury and Venus, which, since formation, have significantly spun down because of tidal interactions5,6. Here we report near-infrared spectroscopic observations, at a resolving power of 100,000, of the young extrasolar gas giant planet β Pictoris b (refs 7, 8). The absorption signal from carbon monoxide in the planet’s thermal spectrum is found to be blueshifted with respect to that from the parent star by approximately 15 kilometres per second, consistent with a circular orbit9. The combined line profile exhibits a rotational broadening of about 25 kilometres per second, meaning that β Pictoris b spins significantly faster than any planet in the Solar System, in line with the extrapolation of the known trend in spin velocity with planet mass.

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Acknowledgements

We thank T. de Zeeuw for granting Director’s Discretionary Time on the VLT to perform these observations (292.C-5017(A)). I.A.G.S. acknowledges support from an NWO VICI grant. R.J.d.K. acknowledges the NWO PEPSci programme.

Author information

Affiliations

  1. Leiden Observatory, Leiden University, Postbus 9513, 2300 RA Leiden, The Netherlands

    • Ignas A. G. Snellen
    • , Bernhard R. Brandl
    • , Remco J. de Kok
    • , Matteo Brogi
    • , Jayne Birkby
    •  & Henriette Schwarz
  2. Netherlands Institute for Space Research (SRON), Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands

    • Remco J. de Kok

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Contributions

I.A.G.S. designed the project with help from B.R.B., R.J.d.K., M.B. and J.B. The analysis was led by I.A.G.S. and he wrote the first version of the manuscript. I.A.G.S. and B.R.B. made the connection with the European Extremely Large Telescope. R.J.d.K. constructed the planet atmosphere models. B.J.B., R.J.d.K., M.B., J.B. and H.S. discussed the analyses and results, and commented on the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Ignas A. G. Snellen.

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https://doi.org/10.1038/nature13253

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