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Astronomy

Exoplanet caught speeding

Nature volume 465, pages 1017–1018 (2010)Cite this article

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The masses of exoplanets have so far been inferred from the tiny gravitational pull they exert on the host stars. It is now possible to measure them from shifts in spectral lines arising from the planets' atmospheres.

Binary stars are gravitationally bound pairs of stars that orbit a common centre of mass. They are valuable systems. For more than a century, they have enabled astronomers to measure the masses of stars directly. All that was needed was to interlace Newton's law of gravitation with measurements of the stars' Doppler shift — the change in the wavelength of their light spectrum that is caused by their motion towards or away from Earth. A star–planet system is also a binary system but is a special case: one of the objects (the planet) is much smaller and fainter than the other (the host star), so that only the star's light, and therefore its Doppler shift (the so-called wobble), can be detected easily. For this reason, the masses of exoplanets have never been measured directly but only inferred — until now. On page 1049 of this issue, Snellen et al.1 provide the first evidence of an exoplanet's Doppler signal, which enabled them to measure the planet's mass directly.

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Figure 1: An exoplanet's Doppler signal.

References

  1. Snellen, I. A. G., de Kok, R. J., de Mooij, E. J. W. & Albrecht, S. Nature 465, 1049–1051 (2010).

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  1. Mercedes López-Morales is in the Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington DC 20015, USA. mercedes@dtm.ciw.edu,

    Mercedes López-Morales

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  1. Mercedes López-Morales
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López-Morales, M. Exoplanet caught speeding. Nature 465, 1017–1018 (2010). https://doi.org/10.1038/4651017a

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