Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Article
  • Published:

Measured spin–orbit alignment of ultra-short-period super-Earth 55 Cancri e

Nature Astronomy volume 7, pages 198–205 (2023)Cite this article

Subjects

An Author Correction to this article was published on 11 January 2023

This article has been updated

Abstract

A planet’s orbital alignment places important constraints on how a planet formed and consequently evolved. The dominant formation pathway of ultra-short-period planets (P < 1 day) is particularly mysterious as such planets most likely formed further out, and it is not well understood what drove their migration inwards to their current positions. Measuring the orbital alignment is difficult for smaller super-Earth/sub-Neptune planets, which give rise to smaller amplitude signals. Here we present radial velocities across two transits of 55 Cancri (Cnc) e, an ultra-short-period super-Earth, observed with the Extreme Precision Spectrograph. Using the classical Rossiter–McLaughlin method, we measure 55 Cnc e’s sky-projected stellar spin–orbit alignment (that is, the projected angle between the planet’s orbital axis and its host star’s spin axis) to be \(\lambda =10\begin{array}{c}+1{7}^{\circ }\\ -20^{\circ }\end{array}\) with an unprojected angle of \(\psi =23\begin{array}{c}+1{4}^{\circ }\\ -12^{\circ }\end{array}\). The best-fit Rossiter–McLaughlin model to the Extreme Precision Spectrograph data has a radial velocity semi-amplitude of just \(0.41\begin{array}{c}+0.09\\ -0.10\end{array}\) m s−1. The spin–orbit alignment of 55 Cnc e favours dynamically gentle migration theories for ultra-short-period planets, namely tidal dissipation through low-eccentricity planet–planet interactions and/or planetary obliquity tides.

This is a preview of subscription content, access via your institution

Access options

Buy this article

  • Purchase on Springer Link
  • Instant access to full article PDF
Buy now

Prices may be subject to local taxes which are calculated during checkout

Fig. 1: RM model fit to two nights of EXPRES RV data.
Fig. 2: A visual representation of the sky-projected alignment between 55 Cnc e’s stellar spin axis and planetary orbit axis.

Similar content being viewed by others

Data availability

The EXPRES radial velocities used in this study are published as part of the Supplementary Information. The TESS data used in this study are publicly available and can be obtained from the Mikulski Archive for Space Telescopes (MAST; https://archive.stsci.edu/missions-and-data/tess).

Code availability

The code associated with this work used only open source software. This research made use of SciPy56, NumPy57,58, Astropy59,60, lightkurve61, starry62, emcee48, celerite35,36, ellc47 and LDTk37. This research also made use of exoplanet31 and its dependencies32,33,59,60,62,63,64.

Change history

References

  1. Butler, R. P., Marcy, G. W., Williams, E., Hauser, H. & Shirts, P. Three new ‘51 Pegasi-type’ planets. Astrophys. J. Lett. 474, L115–L118 (1997).

    Article  ADS  Google Scholar 

  2. Marcy, G. W. et al. A planet at 5 AU around 55 Cancri. Astrophys. J. 581, 1375–1388 (2002).

    Article  ADS  Google Scholar 

  3. McArthur, B. E. et al. Detection of a Neptune-mass planet in the ρ1 Cancri system using the Hobby-Eberly telescope. Astrophys. J. Lett. 614, L81–L84 (2004).

    Article  ADS  Google Scholar 

  4. Fischer, D. A. et al. Five planets orbiting 55 Cancri. Astrophys. J. 675, 790–801 (2008).

    Article  ADS  Google Scholar 

  5. Winn, J. N. et al. A super-Earth transiting a naked-eye star. Astrophys. J. Lett. 737, L18 (2011).

    Article  ADS  Google Scholar 

  6. Demory, B.-O. et al. Detection of a transit of the super-Earth 55 Cancri e with warm Spitzer. Astron. Astrophys. 2, 17.04 (2011).

    Google Scholar 

  7. Dawson, R. I. & Fabrycky, D. C. Radial velocity planets de-aliased: a new, short period for super-Earth 55 Cnc e. Astrophys. J. 722, 937–953 (2010).

    Article  ADS  Google Scholar 

  8. Bourrier, V. et al. The 55 Cancri system reassessed. Astron. Astrophys. 619, A1 (2018).

    Article  Google Scholar 

  9. Steffen, J. H. & Coughlin, J. L. A population of planetary systems characterized by short-period, Earth-sized planets. Proc. Natl Acad. Sci. USA 113, 12023–12028 (2016).

    Article  ADS  Google Scholar 

  10. Dai, F., Masuda, K. & Winn, J. N. Larger mutual inclinations for the shortest-period planets. Astrophys. J. Lett. 864, L38 (2018).

    Article  ADS  Google Scholar 

  11. Petrovich, C., Deibert, E. & Wu, Y. Ultra-short-period planets from secular chaos. Astron. J. 157, 180 (2019).

    Article  ADS  Google Scholar 

  12. Pu, B. & Lai, D. Low-eccentricity migration of ultra-short-period planets in multiplanet systems. Mon. Not. R. Astron. Soc. 488, 3568–3587 (2019).

    Article  ADS  Google Scholar 

  13. Millholland, S. C. & Spalding, C. Formation of ultra-short-period planets by obliquity-driven tidal runaway. Astrophys. J. 905, 71 (2020).

    Article  ADS  Google Scholar 

  14. Triaud, A. H. M. J. in Handbook of Exoplanets (eds Deeg, H. J. & Belmonte, J. A.), Springer International Publishing AG, 2 (2018).

  15. Albrecht, S. H., Dawson, R. I. & Winn, J. N. Stellar obliquities in exoplanetary systems. Publ. Astron. Soc. Pac. 134, 82001 (2022).

    Article  Google Scholar 

  16. Bourrier, V. & Hébrard, G. Detecting the spin-orbit misalignment of the super-Earth 55 Cancri e. Astron. Astrophys. 569, A65 (2014).

    Article  ADS  Google Scholar 

  17. López-Morales, M. et al. Rossiter-McLaughlin observations of 55 Cnc e. Astrophys. J. Lett. 792, L31 (2014).

    Article  ADS  Google Scholar 

  18. Pepe, F. et al. ESPRESSO—An Echelle SPectrograph for Rocky Exoplanets Search and Stable Spectroscopic Observations. Messenger 153, 6–16 (2013).

    ADS  Google Scholar 

  19. Jurgenson, C. et al. in Ground-based and Airborne Instrumentation for Astronomy VI Vol. 9908 of Proc. SPIE, 99086T (eds Evans, C. J., Simard, L. & Takami, H.) (SPIE, 2016).

  20. Brewer, J. M., Fischer, D. A., Valenti, J. A. & Piskunov, N. Spectral properties of cool stars: extended abundance analysis of 1,617 planet-search stars. Astrophys. J. Suppl. 225, 32 (2016).

    Article  ADS  Google Scholar 

  21. Piskunov, N. & Valenti, J. A. Spectroscopy made easy: evolution. Astron. Astrophys. 597, A16 (2017).

    Article  ADS  Google Scholar 

  22. Kunovac Hodžić, V., Triaud, A. H. M. J., Cegla, H. M., Chaplin, W. J. & Davies, G. R. Orbital misalignment of the super-Earth π Men c with the spin of its star. Mon. Not. R. Astron. Soc. 502, 2893–2911 (2021).

    Article  ADS  Google Scholar 

  23. Bourrier, V. et al. The Rossiter-McLaughlin effect revolutions: an ultra-short period planet and a warm mini-Neptune on perpendicular orbits. Astron. Astrophys. 654, A152 (2021).

    Article  Google Scholar 

  24. Valenti, J. A. & Fischer, D. A. Spectroscopic Properties of Cool Stars (SPOCS). I. 1040 F, G, and K dwarfs from Keck, Lick, and AAT planet search programs. Astrophys. J. Suppl. 159, 141–166 (2005).

    Article  ADS  Google Scholar 

  25. Kaib, N. A., Raymond, S. N. & Duncan, M. J. 55 Cancri: a coplanar planetary system that is likely misaligned with its star. Astrophys. J. Lett. 742, L24 (2011).

    Article  ADS  Google Scholar 

  26. Hansen, B. M. S. & Zink, J. On the potentially dramatic history of the super-Earth ρ 55 Cancri e. Mon. Not. R. Astron. Soc. 450, 4505–4520 (2015).

    Article  ADS  Google Scholar 

  27. Boué, G. & Fabrycky, D. C. Compact planetary systems perturbed by an inclined companion. II. Stellar spin-orbit evolution. Astrophys. J. 789, 111 (2014).

    Article  ADS  Google Scholar 

  28. Boué, G. & Fabrycky, D. C. Spin-orbit angle in compact planetary systems perturbed by an inclined companion. Application to the 55 Cancri system. In Complex Planetary Systems, Proceedings of the International Astronomical Union Vol. 310, 62–65 (Cambridge Univ. Press, 2014).

  29. Christiansen, J. L. et al. Three’s company: an additional non-transiting super-Earth in the bright HD 3167 system, and masses for all three planets. Astron. J. 154, 122 (2017).

    Article  ADS  Google Scholar 

  30. Jenkins, J. M. Advances in the Kepler Transit Search Engine. IAU Focus Meet. 29A, 210–212 (2016).

    ADS  Google Scholar 

  31. Foreman-Mackey, D. et al. exoplanet-dev/exoplanet v.0.4.0 Zenodo https://doi.org/10.5281/zenodo.1998447 (2020).

  32. Salvatier, J., Wiecki, T. V. & Fonnesbeck, C. Probabilistic programming in python using pymc3. PeerJ Computer Sci. 2, e55 (2016).

    Article  Google Scholar 

  33. Theano Development Team. Theano: a Python framework for fast computation of mathematical expressions. Preprint at http://arxiv.org/abs/1605.02688 (2016).

  34. von Braun, K. et al. 55 Cancri: stellar astrophysical parameters, a planet in the habitable zone, and implications for the radius of a transiting super-Earth. Astrophys. J. 740, 49 (2011).

    Article  ADS  Google Scholar 

  35. Foreman-Mackey, D., Agol, E., Ambikasaran, S. & Angus, R. Fast and scalable Gaussian process modeling with applications to astronomical time series. Astron. J. 154, 220 (2017).

    Article  ADS  Google Scholar 

  36. Foreman-Mackey, D. Scalable backpropagation for Gaussian processes using Celerite. Res. Notes Am. Astron. Soc. 2, 31 (2018).

    ADS  Google Scholar 

  37. Parviainen, H. & Aigrain, S. LDTK: Limb Darkening Toolkit. Mon. Not. R. Astron. Soc. 453, 3821–3826 (2015).

    Article  ADS  Google Scholar 

  38. Husser, T.-O. et al. A new extensive library of PHOENIX stellar atmospheres and synthetic spectra. Astron. Astrophys. 553, A6 (2013).

    Article  Google Scholar 

  39. Gelman, A., Carlin, J., Stern, H. & Rubin, D. Bayesian Data Analysis 2nd edn, Chapman & Hall/CRC Texts in Statistical Science (Taylor & Francis, 2003); https://books.google.co.uk/books?id=TNYhnkXQSjAC

  40. Demory, B.-O. et al. A map of the large day–night temperature gradient of a super-Earth exoplanet. Nature 532, 207–209 (2016).

    Article  ADS  Google Scholar 

  41. Kipping, D. & Jansen, T. Detection of the occultation of 55 Cancri e with TESS. Res. Notes Am. Astron. Soc. 4, 170 (2020).

    ADS  Google Scholar 

  42. Levine, S. E. et al. in Ground-based and Airborne Telescopes IV Vol. 8444 of Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series 844419 (eds Stepp, L. M., Gilmozzi, R. & Hall, H. J.) (SPIE, 2012).

  43. Blackman, R. T. et al. Performance verification of the EXtreme PREcision Spectrograph. Astron. J. 159, 238 (2020).

    Article  ADS  Google Scholar 

  44. Zhao, L. L. et al. The EXPRES stellar signals project II. State of the field in disentangling photospheric velocities. Astron. J. 163, 171 (2022).

    Article  ADS  Google Scholar 

  45. Petersburg, R. R. et al. An extreme-precision radial-velocity pipeline: first radial velocities from EXPRES. Astron. J. 159, 187 (2020).

    Article  ADS  Google Scholar 

  46. Ohta, Y., Taruya, A. & Suto, Y. The Rossiter-McLaughlin effect and analytic radial velocity curves for transiting extrasolar planetary systems. Astrophys. J. 622, 1118–1135 (2005).

    Article  ADS  Google Scholar 

  47. Maxted, P. F. L. Ellc: a fast, flexible light curve model for detached eclipsing binary stars and transiting exoplanets. Astron. Astrophys. 591, A111 (2016).

    Article  ADS  Google Scholar 

  48. Foreman-Mackey, D., Hogg, D. W., Lang, D. & Goodman, J. emcee: the MCMC hammer. Publ. Astron. Soc. Pac. 125, 306 (2013).

    Article  ADS  Google Scholar 

  49. Cegla, H. M. et al. Modeling the Rossiter-McLaughlin effect: impact of the convective center-to-limb variations in the stellar photosphere. Astrophys. J. 819, 67 (2016).

    Article  ADS  Google Scholar 

  50. Shporer, A. & Brown, T. The Impact of the convective blueshift effect on spectroscopic planetary transits. Astrophys. J. 733, 30 (2011).

    Article  ADS  Google Scholar 

  51. Meunier, N., Mignon, L. & Lagrange, A. M. Variability in stellar granulation and convective blueshift with spectral type and magnetic activity. II. From young to old main-sequence K-G-F stars. Astron. Astrophys. 607, A124 (2017).

    Article  ADS  Google Scholar 

  52. Liebing, F., Jeffers, S. V., Reiners, A. & Zechmeister, M. Convective blueshift strengths of 810 F to M solar-type stars. Astron. Astrophys. 654, A168 (2021).

    Article  ADS  Google Scholar 

  53. Masuda, K. & Winn, J. N. On the inference of a star’s inclination angle from its rotation velocity and projected rotation velocity. Astronom. J. 159, 81 (2020).

    Article  ADS  Google Scholar 

  54. Andrae, R., Schulze-Hartung, T. & Melchior, P. Dos and don’ts of reduced chi-squared. Preprint at https://arxiv.org/abs/1012.3754 (2010).

  55. Schwarz, G. Estimating the dimension of a model. Ann. Stat. 6, 461–464 (1978).

    Article  MathSciNet  MATH  Google Scholar 

  56. Virtanen, P. et al. SciPy 1.0: fundamental algorithms for scientific computing in Python. Nat. Methods 17, 261–272 (2020).

    Article  Google Scholar 

  57. Oliphant, T. NumPy: A Guide to NumPy (Trelgol Publishing, 2006); http://www.numpy.org/

  58. van der Walt, S., Colbert, S. C. & Varoquaux, G. The numpy array: a structure for efficient numerical computation. Comput. Sci. Eng. 13, 22–30 (2011).

    Article  Google Scholar 

  59. Astropy Collaboration. Astropy: a community Python package for astronomy. Astron. Astrophys. 558, A33 (2013).

    Article  Google Scholar 

  60. Price-Whelan, A. M. et al. The Astropy Project: building an open-science project and status of the v2.0 core package. Astron. J. 156, 123 (2018).

    Article  ADS  Google Scholar 

  61. Lightkurve Collaboration. Lightkurve: Kepler and TESS time series analysis in Python (Astrophysics Source Code Library, 2018).

  62. Luger, R. et al. starry: analytic occultation light curves. Astron. J. 157, 64 (2019).

    Article  ADS  Google Scholar 

  63. Agol, E., Luger, R. & Foreman-Mackey, D. Analytic planetary transit light curves and derivatives for stars with polynomial limb darkening. Astron. J. 159, 123 (2020).

    Article  ADS  Google Scholar 

  64. Kipping, D. M. Efficient, uninformative sampling of limb darkening coefficients for two-parameter laws. Mon. Not. R. Astron. Soc. 435, 2152–2160 (2013).

    Article  ADS  Google Scholar 

Download references

Acknowledgements

These results made use of data provided by the EXPRES team using the Extreme Precision Spectrograph at the Lowell Discovery Telescope, Lowell Observatory. Lowell is a private, non-profit institution dedicated to astrophysical research and public appreciation of astronomy and operates the LDT in partnership with Boston University, the University of Maryland, the University of Toledo, Northern Arizona University and Yale University. EXPRES was designed and built at Yale with financial support from grants NSF MRI-1429365 and NSF ATI-1509436 and Yale University. Research with EXPRES is possible thanks to the generous support from grants NSF AST-2009528, NSF 1616086 and NASA 80NSSC18K0443, the Heising-Simons Foundation and an anonymous donor in the Yale alumni community. This paper includes data collected with the TESS mission, obtained from the MAST data archive at the Space Telescope Science Institute (STScI). Funding for the TESS mission is provided by the NASA Explorer Program. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract no. NAS 5-26555. V.K. and J.L. acknowledge support from NSF award nos. AST-2009501 and AST-2009343. J.M.B. acknowledges support from NASA grant nos. 80NSSC21K0009 and 80NSSC21K0571. R.M.R. acknowledges support from the Heising-Simons 51 Pegasi b Postdoctoral Fellowship.

Author information

Authors and Affiliations

  1. Center for Computational Astrophysics, Flatiron Institute, Simons Foundation, New York, NY, USA

    Lily L. Zhao

  2. Lowell Observatory, Flagstaff, AZ, USA

    Vedad Kunovac & Joe Llama

  3. Department of Astronomy and Planetary Science, Northern Arizona University, Flagstaff, AZ, USA

    Vedad Kunovac

  4. Department of Physics & Astronomy, San Francisco State University, San Francisco, CA, USA

    John M. Brewer

  5. MIT Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA, USA

    Sarah C. Millholland

  6. University of Maryland, Baltimore County, Baltimore, MD, USA

    Christina Hedges

  7. NASA Goddard Space Flight Center, Greenbelt, MD, USA

    Christina Hedges

  8. Department of Astronomy, Yale University, New Haven, CT, USA

    Andrew E. Szymkowiak, Rachael M. Roettenbacher, Samuel H. C. Cabot, Sam A. Weiss & Debra A. Fischer

  9. Department of Physics, Yale University, New Haven, CT, USA

    Andrew E. Szymkowiak

  10. Department of Astronomy, University of Michigan, Ann Arbor, MI, USA

    Rachael M. Roettenbacher

Authors
  1. Lily L. Zhao
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Vedad Kunovac
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. John M. Brewer
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Joe Llama
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. Sarah C. Millholland
    View author publications

    You can also search for this author in PubMed Google Scholar

  6. Christina Hedges
    View author publications

    You can also search for this author in PubMed Google Scholar

  7. Andrew E. Szymkowiak
    View author publications

    You can also search for this author in PubMed Google Scholar

  8. Rachael M. Roettenbacher
    View author publications

    You can also search for this author in PubMed Google Scholar

  9. Samuel H. C. Cabot
    View author publications

    You can also search for this author in PubMed Google Scholar

  10. Sam A. Weiss
    View author publications

    You can also search for this author in PubMed Google Scholar

  11. Debra A. Fischer
    View author publications

    You can also search for this author in PubMed Google Scholar

Contributions

L.L.Z. designed the project and drafted the manuscript. V.K. led the analysis and drafted the manuscript. S.C.M. contributed to the scientific interpretation. C.H. processed the TESS data. L.L.Z., J.M.B., J.L., A.E.S., R.M.R., S.H.C.C., S.A.W. and D.A.F. are members of the EXPRES team that built and commissioned EXPRES, maintain the instrument for high precision work and supervise the data reduction pipeline. D.A.F. is the PI of the EXPRES Team and derived the EXPRES RVs. J.M.B. ran the stellar parameter analysis. L.L.Z., V.K., J.M.B., J.L., S.H.C.C., S.A.W. and D.A.F. contributed to the EXPRES observations.

Corresponding author

Correspondence to Lily L. Zhao.

Ethics declarations

Competing interests

The authors declare no competing interests.

Peer review

Peer review information

Nature Astronomy thanks Teruyuki Hirano and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

Additional information

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary Information

Supplementary Figs. 1–2 and Tables 1–4.

Supplementary Data

EXPRES RVs used in this work.

Rights and permissions

Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Zhao, L.L., Kunovac, V., Brewer, J.M. et al. Measured spin–orbit alignment of ultra-short-period super-Earth 55 Cancri e. Nat Astron 7, 198–205 (2023). https://doi.org/10.1038/s41550-022-01837-2

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/s41550-022-01837-2

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing