Letter | Published:

Interstellar turbulence spectrum from in situ observations of Voyager 1

Abstract

Interstellar scintillation of radio waves from pulsars reveals that the interstellar turbulence spectrum of electron density approximates the Kolmogorov power law from wavenumber \(q = 10^{ - 18}\,{\rm{m}}^{ - 1}\) to \(10^{ - 6.5}\,{\mathrm{m}}^{ - 1}\) (refs. 1,2,3,4,5). Here we obtain the interstellar turbulence spectrum of electron density from in situ observations of Voyager 1. The observed spectrum extends from \(\lambda = 15\,{\mathrm{au}} \approx {\mathrm{2}}{\mathrm{.25}} \times {\mathrm{10}}^{12}\,{\mathrm{m}}\) (\(q = 4.4 \times 10^{ - 13}\,{\mathrm{m}}^{ - 1}\)) to \(\lambda = q^{ - 1}\) = 50 m (\(q = {\mathrm{2}} \times {\mathrm{10}}^{ - 2}\,{\mathrm{m}}^{ - 1}\)), close to the Debye length. The measured spectrum covers part (\(q = 4.4 \times 10^{ - 13}\,{\mathrm{m}}^{ - 1}\,{\mathrm{to}}\,1 \times 10^{ - 6}\,{\mathrm{m}}^{ - 1}\)) of the Kolmogorov inertial range, as well as ion and electron kinetic scales (\(q = 10^{ - 6}\,{\mathrm{m}}^{ - 1} \,{\mathrm{to }}\, {\mathrm{2}} \times {\mathrm{10}}^{ - 2}\,{\mathrm{m}}^{ - 1}\)). The observed Kolmogorov inertial range shows good agreement with earlier studies by Lee and Jokipii2 and Armstrong et al.3,4. Around the kinetic scales, a bulge of spectral intensity higher than the Kolmogorov spectrum is found.

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Data availability

The Voyager 1 data that support the findings of this study are available from the Planetary Plasma Interactions Node of the Planetary Data System archives: https://pds-ppi.igpp.ucla.edu/index.jsp.

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Acknowledgements

The research was supported by the Ministry of Science and Technology in Taiwan (MOST 106-2111-M-001-012 and 107-2111-M-002-015) and Science and Technology Development Fund of Macao (0035/2018/AFJ). We thank the PWS team of the Voyager mission for the plasma wave data. The Voyager data are downloaded from https://pds-ppi.igpp.ucla.edu/.

Author information

L.C.L. conceived the idea and supervised the project. K.H.L. analysed the data. Both authors contributed to writing the manuscript.

Competing interests

The authors declare no competing interests.

Correspondence to K. H. Lee or L. C. Lee.

Supplementary information

  1. Supplementary Information

    Supplementary Figures 1–5, Supplementary references.

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Fig. 1: Dynamic spectra observed in the local ISM by Voyager 1.
Fig. 2: Composite spectrum (red, blue, green and purple dots) obtained from in situ Voyager 1 data.