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:

An Earth-mass planet and a brown dwarf in orbit around a white dwarf

Nature Astronomy (2024)Cite this article

Subjects

Abstract

It has been theorized that terrestrial planets born beyond 1–3 au could avoid being engulfed during the red-giant phases of their host stars. Nevertheless, only a few gas-giant planets have been observed around white dwarfs (WDs), the end product left behind by a red giant. Here we report on evidence that the lens system that produced the microlensing event KMT-2020-BLG-0414 is composed of a WD orbited by an Earth-mass planet and a brown dwarf companion, as shown by the non-detection of the lens flux using Keck adaptive optics. From microlensing orbital motion constraints, we determine the planet to be a 1.9 ± 0.2 Earth-mass (M⊕) planet at a physical separation of 2.1 ± 0.2 au from the WD during the event. By considering the system’s evolutionary history, we determine the brown dwarf companion to have a projected separation of 22 au from the WD and reject a degenerate model that places the brown dwarf at 0.2 au. Given the planetary orbital expansion during the final evolutionary stages of the host star, this Earth-mass planet may have existed in an initial orbit close to 1 au, thereby offering a glimpse into the possible survival of planet Earth in the distant future.

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

Access options

Buy this article

  • Purchase on SpringerLink
  • Instant access to full article PDF
Buy now

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

Fig. 1: OGLE-III, CFHT and Keck II imaging of KMT-2020-BLG-0414 taken before, during and after the event.
Fig. 2: Planet’s physical separation from the WD host during the peak of the event as inferred from its projected separation and the microlensing orbital motion.
Fig. 3: Illustration of the system’s possible evolutionary histories under the close NE and wide NE models.

Similar content being viewed by others

Data availability

The reduced Keck images are available via Zenodo at https://doi.org/10.5281/zenodo.13128167 (ref. 61). The raw data will be available on the Keck Observatory Archive (https://koa.ipac.caltech.edu/) after the 18-month proprietary period.

References

  1. Zang, W. et al. An Earth-mass planet in a time of COVID-19: KMT-2020-BLG-0414Lb. Res. Astron. Astrophys. 21, 239 (2021).

    Article  ADS  Google Scholar 

  2. Dominik, M. The binary gravitational lens and its extreme cases. Astron. Astrophys. 349, 108–125 (1999).

    ADS  Google Scholar 

  3. Jiang, G. et al. OGLE-2003-BLG-238: microlensing mass estimate of an isolated star. Astrophys. J. 617, 1307 (2004).

    Article  ADS  Google Scholar 

  4. Poindexter, S. et al. Systematic analysis of 22 microlensing parallax candidates. Astrophys. J. 633, 914 (2005).

    Article  ADS  Google Scholar 

  5. Wizinowich, P. L. et al. The W. M. Keck Observatory laser guide star adaptive optics system: overview. Publ. Astron. Soc. Pac. 118, 297–309 (2006).

    Article  ADS  Google Scholar 

  6. van Dam, M. A. et al. The W. M. Keck Observatory laser guide star adaptive optics system: performance characterization. Publ. Astron. Soc. Pac. 118, 310–318 (2006).

    Article  ADS  Google Scholar 

  7. Brown, W. R. et al. The ELM survey. VIII. Ninety-eight double white dwarf binaries. Astrophys. J. 889, 49 (2020).

    Article  ADS  Google Scholar 

  8. Brown, W. R., Kilic, M., Kosakowski, A. & Gianninas, A. The ELM Survey. IX. A complete sample of low-mass white dwarf binaries in the SDSS footprint. Astrophys. J. 933, 94 (2022).

    Article  ADS  Google Scholar 

  9. Sun, M. & Arras, P. Formation of extremely low-mass white dwarf binaries. Astrophys. J. 858, 14 (2018).

    Article  ADS  Google Scholar 

  10. Li, Z., Chen, X., Chen, H.-L. & Han, Z. Formation of extremely low-mass white dwarfs in double degenerates. Astrophys. J. 871, 148 (2019).

    Article  ADS  Google Scholar 

  11. Zorotovic, M., Schreiber, M. R., Gänsicke, B. T. & Nebot Gómez-Morán, A. Post-common-envelope binaries from SDSS. IX. Constraining the common-envelope efficiency. Astron. Astrophys. 520, A86 (2010).

    Article  ADS  Google Scholar 

  12. Belloni, D., Zorotovic, M., Schreiber, M. R., Parsons, S. G. & Garbutt, J. A. Formation of long-period post-common-envelope binaries. I. No extra energy is needed to explain oxygen-neon white dwarfs paired with AFGK-type main-sequence stars. Astron. Astrophys. 686, A61 (2024).

    Article  Google Scholar 

  13. Falcon, R. E., Winget, D. E., Montgomery, M. H. & Williams, K. A. A gravitational redshift determination of the mean mass of white dwarfs. DA stars. Astrophys. J. 712, 585–595 (2010).

    Article  ADS  Google Scholar 

  14. Kilic, M. et al. The 100 pc white dwarf sample in the SDSS footprint. Astrophys. J. 898, 84 (2020).

    Article  ADS  Google Scholar 

  15. Chen, J. & Kipping, D. Probabilistic forecasting of the masses and radii of other worlds. Astrophys. J. 834, 17 (2016).

    Article  ADS  Google Scholar 

  16. Otegi, J. F., Bouchy, F. & Helled, R. Revisited mass-radius relations for exoplanets below 120 M⊕. Astron. Astrophys. 634, A43 (2020).

    Article  ADS  Google Scholar 

  17. Cummings, J. D., Kalirai, J. S., Tremblay, P.-E., Ramirez-Ruiz, E. & Choi, J. The white dwarf initial-final mass relation for progenitor stars from 0.85 to 7.5 M⊙. Astrophys. J. 866, 21 (2018).

    Article  ADS  Google Scholar 

  18. Dong, S. et al. Microlensing event MOA-2007-BLG-400: exhuming the buried signature of a cool, Jovian-mass planet. Astrophys. J. 698, 1826–1837 (2009).

    Article  ADS  Google Scholar 

  19. Skowron, J. et al. Binary microlensing event OGLE-2009-BLG-020 gives verifiable mass, distance, and orbit predictions. Astrophys. J. 738, 87 (2011).

    Article  ADS  Google Scholar 

  20. Jackson, B., Greenberg, R. & Barnes, R. Tidal evolution of close-in extrasolar planets. Astrophys. J. 678, 1396 (2008).

    Article  ADS  Google Scholar 

  21. Jones, M. I., Jenkins, J. S., Bluhm, P., Rojo, P. & Melo, C. H. F. The properties of planets around giant stars. Astron. Astrophys. 566, A113 (2014).

    Article  ADS  Google Scholar 

  22. Kass, R. E. & Raftery, A. E. Bayes factors. J. Am. Stat. Assoc. 90, 773–795 (1995).

    Article  MathSciNet  Google Scholar 

  23. Ida, S. & Lin, D. N. C. Toward a deterministic model of planetary formation. I. A desert in the mass and semimajor axis distributions of extrasolar planets. Astrophys. J. 604, 388 (2004).

    Article  ADS  Google Scholar 

  24. Rasio, F. A. & Ford, E. B. Dynamical instabilities and the formation of extrasolar planetary systems. Science 274, 954–956 (1996).

    Article  ADS  Google Scholar 

  25. Gould, A. et al. Free-floating planets, the Einstein desert, and ‘Oumuamua. J. Korean Astron. Soc. 55, 173–194 (2022).

    ADS  Google Scholar 

  26. Sumi, T. et al. Free-floating planet mass function from MOA-II 9-year survey towards the Galactic bulge. Astron. J. 166, 108 (2023).

    Article  ADS  Google Scholar 

  27. Mróz, P., Ban, M., Marty, P. & Poleski, R. Free-floating or wide-orbit? Keck adaptive-optics observations reveal no host stars near free-floating planet candidates. Astron. J. 167, 40 (2023).

    Article  ADS  Google Scholar 

  28. Nelson, L., Schwab, J., Ristic, M. & Rappaport, S. Minimum orbital period of precataclysmic variables. Astrophys. J. 866, 88 (2018).

    Article  ADS  Google Scholar 

  29. Kruse, E. & Agol, E. KOI-3278: a self-lensing binary star system. Science 344, 275–277 (2014).

    Article  ADS  Google Scholar 

  30. Kawahara, H. et al. Discovery of three self-lensing binaries from Kepler. Astron. J. 155, 144 (2018).

    Article  ADS  Google Scholar 

  31. Yamaguchi, N. et al. Wide post-common envelope binaries containing ultramassive white dwarfs: evidence for efficient envelope ejection in massive asymptotic giant branch stars. Mon. Not. R. Astron. Soc. 527, 11719–11739 (2024).

    Article  ADS  Google Scholar 

  32. Izzard, R. G. & Jermyn, A. S. Post-AGB discs from common-envelope evolution. Galaxies 6, 97 (2018).

    Article  ADS  Google Scholar 

  33. Deck, K. M., Payne, M. & Holman, M. J. First-order resonance overlap and the stability of close two-planet systems. Astrophys. J. 774, 129 (2013).

    Article  ADS  Google Scholar 

  34. Guo, J., Lin, L., Bai, C. & Liu, J. The effects of solar Reimers’ η on the final destinies of Venus, the Earth, and Mars. Astrophys. Space Sci. 361, 122 (2016).

    Article  ADS  Google Scholar 

  35. McDonald, I. & Zijlstra, A. A. Mass-loss on the red giant branch: the value and metallicity dependence of Reimers’ η in globular clusters. Mon. Not. R. Astron. Soc. 448, 502–521 (2015).

    Article  ADS  Google Scholar 

  36. Schröder, K.-P. & Connon Smith, R. Distant future of the Sun and Earth revisited. Mon. Not. R. Astron. Soc. 386, 155–163 (2008).

    Article  ADS  Google Scholar 

  37. Lanza, A. F., Lebreton, Y. & Sallard, C. Residual eccentricity of an Earth-like planet orbiting a red giant Sun. Astron. Astrophys. 674, A176 (2023).

    Article  ADS  Google Scholar 

  38. Mao, S. & Paczyński, B. Gravitational microlensing by double stars and planetary pystems. Astrophys. J. 374, L37 (1991).

    Article  ADS  Google Scholar 

  39. Gould, A. & Loeb, A. Discovering planetary systems through gravitational microlenses. Astrophys. J. 396, 104–114 (1992).

    Article  ADS  Google Scholar 

  40. Metchev, S. A. & Hillenbrand, L. A. The Palomar/Keck adaptive optics survey of young solar analogs: evidence for a universal companion mass function. Astrophys. J. Suppl. Ser. 181, 62 (2009).

    Article  ADS  Google Scholar 

  41. Bradley, L. et al. astropy/photutils: 1.5.0. Zenodo https://doi.org/10.5281/zenodo.10967176 (2022).

  42. Minniti, D. et al. VISTA variables in the Via Lactea (VVV): the public ESO near-IR variability survey of the Milky Way. New Astron. 15, 433–443 (2010).

    Article  ADS  Google Scholar 

  43. Nataf, D. M. et al. Reddening and extinction toward the Galactic bulge from Ogle-III: the inner Milky Way’s RV ~ 2.5 extinction curve. Astrophys. J. 769, 88 (2013).

    Article  ADS  Google Scholar 

  44. Nataf, D. M. et al. Interstellar extinction curve variations towards the inner Milky Way: a challenge to observational cosmology. Mon. Not. R. Astron. Soc. 456, 2692–2706 (2016).

    Article  ADS  Google Scholar 

  45. Gonzalez, O. A. et al. Reddening and metallicity maps of the Milky Way bulge from VVV and 2MASS. II. The complete high resolution extinction map and implications for Galactic bulge studies. Astron. Astrophys. 543, A13 (2012).

    Article  Google Scholar 

  46. Nishiyama, S. et al. Interstellar extinction law toward the Galactic Center. III. J, H, KS bands in the 2MASS and the MKO systems, and 3.6, 4.5, 5.8, 8.0 μm in the Spitzer/IRAC system. Astrophys. J. 696, 1407 (2009).

    Article  ADS  Google Scholar 

  47. Bessell, M. S. & Brett, J. M. JHKLM photometry: standard systems, passbands, and intrinsic colors. Publ. Astron. Soc. Pac. 100, 1134 (1988).

    Article  ADS  Google Scholar 

  48. Carpenter, J. M. Color transformations for the 2MASS second incremental data release. Astron. J. 121, 2851–2871 (2001).

    Article  ADS  Google Scholar 

  49. Paxton, B. et al. Modules for Experiments in Stellar Astrophysics (MESA). Astrophys. J. Suppl. Ser. 192, 3 (2011).

    Article  ADS  Google Scholar 

  50. Choi, J. et al. Mesa Isochrones and Stellar Tracks (MIST). I. Solar-scaled models. Astrophys. J. 823, 102 (2016).

    Article  ADS  Google Scholar 

  51. Dotter, A. MESA Isochrones and Stellar Tracks (MIST). 0. methods for the construction of stellar isochrones. Astrophys. J. Suppl. Ser. 222, 8 (2016).

    Article  ADS  Google Scholar 

  52. Zhang, K. et al. Real-time likelihood-free inference of roman binary microlensing events with amortized neural posterior estimation. Astron. J. 161, 262 (2021).

    Article  ADS  Google Scholar 

  53. Zhang, K., Gaudi, B. S. & Bloom, J. S. A ubiquitous unifying degeneracy in two-body microlensing systems. Nat. Astron. 6, 782–787 (2022).

    Article  ADS  Google Scholar 

  54. Zhu, W. et al. Toward a Galactic distribution of planets. I. Methodology and planet sensitivities of the 2015 high-cadence Spitzer microlens sample. Astron. J. 154, 210 (2017).

    Article  ADS  Google Scholar 

  55. Yang, H. et al. KMT-2021-BLG-0171Lb and KMT-2021-BLG-1689Lb: two microlensing planets in the KMTNet high-cadence fields with followup observations. Mon. Not. R. Astron. Soc. 516, 1894–1909 (2022).

    Article  ADS  Google Scholar 

  56. Li, L. et al. Three-dimensional structure of the Milky Way dust: modeling of LAMOST data. Astrophys. J. 858, 75 (2018).

    Article  ADS  Google Scholar 

  57. Gillessen, S. et al. Monitoring stellar orbits around the massive black hole in the Galactic Center. Astrophys. J. 692, 1075 (2009).

    Article  ADS  Google Scholar 

  58. Maíz-Apellániz, J. The spatial distribution of O-B5 stars in the solar neighborhood as measured by Hipparcos. Astron. J. 121, 2737 (2001).

    Article  ADS  Google Scholar 

  59. Salaris, M., Cassisi, S., Pietrinferni, A., Kowalski, P. M. & Isern, J. A large stellar evolution database for population synthesis studies. VI. White dwarf cooling sequences. Astrophys. J. 716, 1241 (2010).

    Article  ADS  Google Scholar 

  60. Foreman-Mackey, D. et al. exoplanet: gradient-based probabilistic inference for exoplanet data & other astronomical time series. J. Open Source Softw. 6, 3285 (2021).

    Article  ADS  Google Scholar 

  61. Zhang, K. Reduced Keck images for KMT-2020-BLG-0414. Zenodo https://doi.org/10.5281/zenodo.13128167 (2024).

Download references

Acknowledgements

K.Z. is supported by the Eric and Wendy Schmidt AI in Science Postdoctoral Fellowship, a Schmidt Futures programme. K.Z. and J.S.B. were partially supported by the Gordon and Betty Moore Foundation and a grant from the National Science Foundation (Award No. 2206744). W.Z. acknowledges support from the Harvard-Smithsonian Center for Astrophysics through a fellowship. W.Z. and S.M. acknowledge support from the National Natural Science Foundation of China (Grant No. 12133005). J.R.L. acknowledges support from the National Science Foundation (Grant No. 1909641) and the Heising-Simons Foundation (Grant No. 2022-3542). K.Z. thanks M. He for assistance on an initial version of the cover art proposal. W.Z. thanks H. Wang for fruitful discussions on the Keck proposal. This research has made use of the KMTNet system operated by the Korea Astronomy and Space Science Institute. The data were obtained at three host sites, namely the Cerro Tololo Inter-American Observatory in Chile, the South African Astronomical Observatory in South Africa and the Siding Spring Observatory in Australia. Data transfer from a host site to the Korea Astronomy and Space Science Institute was supported by the Korea Research Environment Open Network. Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c)3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration (NASA). The observatory was made possible by the generous financial support of the W. M. Keck Foundation. We recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the Native Hawaiian community. We are most fortunate to have had the opportunity to conduct observations from this mountain. This research uses data obtained through the Telescope Access Program, which was funded by member institutes and was partly based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and DAPNIA, which is a part of the French Alternative Energies and Atomic Energy Commission, at the CFHT, which is operated by the National Research Council of Canada, the Institut National des Science de l’Univers of the French National Centre for Scientific Research and the University of Hawaii. The observations at the CFHT were performed with care and respect at the summit of Mauna Kea, which is a significant cultural and historic site.

Author information

Authors and Affiliations

  1. Department of Astronomy and Astrophysics, University of California, San Diego, San Diego, CA, USA

    Keming Zhang & Quinn Konopacky

  2. Halıcıoğlu Data Science Institute, University of California, San Diego, San Diego, CA, USA

    Keming Zhang

  3. Department of Astronomy, University of California, Berkeley, Berkeley, CA, USA

    Keming Zhang, Jessica R. Lu, Joshua S. Bloom, Natalie LeBaron & Sean Terry

  4. Department of Astronomy, Tsinghua University, Beijing, China

    Weicheng Zang & Shude Mao

  5. Center for Astrophysics, Harvard & Smithsonian, Cambridge, MA, USA

    Weicheng Zang

  6. Department of Astronomy, California Institute of Technology, Pasadena, CA, USA

    Kareem El-Badry

  7. Department of Astronomy, University of Washington, Seattle, WA, USA

    Eric Agol

  8. Department of Astronomy, The Ohio State University, Columbus, OH, USA

    B. Scott Gaudi

  9. Department of Astronomy, University of Maryland, College Park, MD, USA

    Sean Terry

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

    Sean Terry

Authors
  1. Keming Zhang
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Weicheng Zang
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Kareem El-Badry
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Jessica R. Lu
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. Joshua S. Bloom
    View author publications

    You can also search for this author in PubMed Google Scholar

  6. Eric Agol
    View author publications

    You can also search for this author in PubMed Google Scholar

  7. B. Scott Gaudi
    View author publications

    You can also search for this author in PubMed Google Scholar

  8. Quinn Konopacky
    View author publications

    You can also search for this author in PubMed Google Scholar

  9. Natalie LeBaron
    View author publications

    You can also search for this author in PubMed Google Scholar

  10. Shude Mao
    View author publications

    You can also search for this author in PubMed Google Scholar

  11. Sean Terry
    View author publications

    You can also search for this author in PubMed Google Scholar

Contributions

K.Z. reduced the Keck data, developed the probabilistic framework for inferring the planet’s physical separation, led the overall analysis and interpretation, and wrote the paper. K.Z., K.E.-B. and E.A. developed the interpretation of the system’s evolutionary history. K.Z. and W.Z. conceived of the observations and led the writing of the Keck proposal. W.Z. contributed to the extinction and lens light analysis. K.Z. and J.S.B. obtained the observing time as the Science PI and PI of Keck programme U152. J.R.L., S.T., J.S.B. and N.L. contributed to the observing. All co-authors participated in discussions and contributed to the revision of the paper.

Corresponding authors

Correspondence to Keming Zhang or Weicheng Zang.

Ethics declarations

Competing interests

The authors declare no competing interests.

Peer review

Peer review information

Nature Astronomy thanks the anonymous reviewers 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.

Extended data

Extended Data Fig. 1 Marginal likelihood for the inclination and orbital phase for different assumed eccentricities.

Shown for the special case of ω = ± π/2 where apastron and periastron are aligned with conjunction for eccentric orbits.

Extended Data Table 1 Orbital motion parameters for the NE models
Full size table

Supplementary information

Supplementary Information

Supplementary Figs. 1–3 and Table 1.

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

Zhang, K., Zang, W., El-Badry, K. et al. An Earth-mass planet and a brown dwarf in orbit around a white dwarf. Nat Astron (2024). https://doi.org/10.1038/s41550-024-02375-9

Download citation

  • Received:

  • Accepted:

  • Published:

  • DOI: https://doi.org/10.1038/s41550-024-02375-9

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