Skip to main content

Thank you for visiting 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.

Multi-phase volcanic resurfacing at Loki Patera on Io


The Jovian moon Io hosts the most powerful persistently active volcano in the Solar System, Loki Patera1,2. The interior of this volcanic, caldera-like feature is composed of a warm, dark floor covering 21,500 square kilometres3 surrounding a much cooler central ‘island’4. The temperature gradient seen across areas of the patera indicates a systematic resurfacing process4,5,6,7,8,9, which has been seen to occur typically every one to three years since the 1980s5,10. Analysis of past data has indicated that the resurfacing progressed around the patera in an anti-clockwise direction at a rate of one to two kilometres per day, and that it is caused either by episodic eruptions that emplace voluminous lava flows or by a cyclically overturning lava lake contained within the patera5,8,9,11. However, spacecraft and telescope observations have been unable to map the emission from the entire patera floor at sufficient spatial resolution to establish the physical processes at play. Here we report temperature and lava cooling age maps of the entire patera floor at a spatial sampling of about two kilometres, derived from ground-based interferometric imaging of thermal emission from Loki Patera obtained on 8 March 2015 ut as the limb of Europa occulted Io. Our results indicate that Loki Patera is resurfaced by a multi-phase process in which two waves propagate and converge around the central island. The different velocities and start times of the waves indicate a non-uniformity in the lava gas content and/or crust bulk density across the patera.

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

Relevant articles

Open Access articles citing this article.

Access options

Rent or buy this article

Get just this article for as long as you need it


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

Figure 1: Observations of Europa occulting Io.
Figure 2: Occultation light curve.
Figure 3: Temperature and age maps of Loki Patera.
Figure 4: Overturn diagrams.


  1. Davies, A. G. in Volcanism on Io: A Comparison with Earth 217–228 (Cambridge Univ. Press, 2007)

  2. Lopes, R. & Spencer, J. (eds) Io after Galileo (Springer-Praxis, 2007)

  3. Veeder, G. et al. Io: heat flow from dark paterae. Icarus 212, 236–261 (2011)

    Article  ADS  Google Scholar 

  4. Lopes-Gautier, R. et al. A close-up look at Io from Galileo’s Near-Infrared Mapping Spectrometer. Science 288, 1201–1204 (2000)

    Article  ADS  CAS  Google Scholar 

  5. Rathbun, J., Spencer, J., Davies, A. G., Howell, R. & Wilson, L. Loki, Io: a periodic volcano. Geophys. Res. Lett. 29, (2002)

  6. Spencer, J. et al. Io’s thermal emission from the Galileo Photopolarimeter-Radiometer. Science 288, 1198–1201 (2000)

    Article  ADS  CAS  Google Scholar 

  7. Rathbun, J. et al. Mapping of Io’s thermal radiation by the Galileo Photopolarimeter-Radiometer (PPR) instrument. Icarus 169, 127–139 (2004)

    Article  ADS  CAS  Google Scholar 

  8. Howell, R. & Lopes, R. The nature of volcanic activity at Loki: insights from Galileo NIMS and PPR data. Icarus 186, 448–461 (2007)

    Article  ADS  Google Scholar 

  9. Davies, A. G. Temperature, age and crust thickness distributions of Loki Patera on Io from Galileo NIMS data: implications for resurfacing mechanism. Geophys. Res. Lett. 30, 2133 (2003)

    Article  ADS  Google Scholar 

  10. Veeder, G., Matson, D., Johnson, T., Blaney, D. & Goguen, J. Io’s heat flow from infrared radiometry: 1983–1993. J. Geophys. Res. 99, 17095–17162 (1994)

    Article  ADS  Google Scholar 

  11. Howell, R. Thermal emission from lava flows on Io. Icarus 127, 394–407 (1997)

    Article  ADS  Google Scholar 

  12. Esposito, S. et al. Large Binocular Telescope Adaptive Optics system: new achievements and perspectives in adaptive optics. Proc. SPIE 8149, 814902 (2011)

    Article  Google Scholar 

  13. Hinz, P. et al. First AO-corrected interferometry with LBTI: steps towards routine coherent imaging observations. Proc. SPIE 8445, 84450U (2012)

    Article  Google Scholar 

  14. Leisenring, J. et al. On-sky operations and performance of LMIRcam at the Large Binocular Telescope. Proc. SPIE 8446, 84464F (2012)

    Article  Google Scholar 

  15. Spencer, J., Clark, B., Toomey, D., Woodney, L. & Sinton, W. Io hot spots in 1991: results from Europa occultation photometry and infrared imaging. Icarus 107, 195–208 (1994)

    Article  ADS  Google Scholar 

  16. de Kleer, K. & de Pater, I. Io’s Loki Patera: modeling of three brightening events in 2013–2016. Icarus 289, 181–198 (2017)

    Article  ADS  Google Scholar 

  17. Turtle, E. et al. The final Galileo SSI observations of Io: orbits G28–O33. Icarus 169, 3–28 (2004)

    Article  ADS  Google Scholar 

  18. Matson, D. et al. Io: Loki Patera as a magma sea. J. Geophys. Res. 111, 2156–2022 (2006)

    Article  Google Scholar 

  19. Veeder, G. et al. Io: Volcanic thermal sources and global heat flow. Icarus 219, 701–722 (2012)

    Article  ADS  Google Scholar 

  20. Hill, J. M., Green, R. F. & Slagle, J. H. The Large Binocular Telescope. Proc. SPIE 6267, 62670Y (2006)

    Article  ADS  Google Scholar 

  21. Leisenring, J. et al. Fizeau interferometric imaging of Io volcanism with LBTI/LMIRcam. Proc. SPIE 9146, 91462S (2014)

    Article  Google Scholar 

  22. Maire, A.-L. et al. The LEECH exoplanet imaging survey. Further constraints on the planet architecture of the HR 8799 system. Astron. Astrophys. 576, A133 (2015)

    Article  Google Scholar 

  23. Conrad, A. et al. Spatially resolved M-band emission from Io’s Loki Patera — Fizeau imaging at the 22.8 m LBT. Astron. J. 149, 175–184 (2015)

    Article  ADS  Google Scholar 

  24. Lim, P. L ., Diaz, R. I. & Laidler, V. PySynphot Users Guide (STSci, 2015)

  25. Foreman-Mackey, D. et al. emcee: the MCMC hammer. Publ. Astron. Soc. Pacif. 125, 925 (2013)

    Article  Google Scholar 

  26. Byrd, R ., Lu, P ., Nocedal, J . & Schnabel, R. A limited memory algorithm for bound constrained optimization. SIAM J. Sci. Statist. Comput. 16, 1190–1208 (1995)

    Article  MathSciNet  Google Scholar 

  27. Dembo, R. & Steihaug, R. Truncated-Newtonian algorithms for large-scale unconstrained optimization. Math. Program. 26, 190–212 (1983)

    Article  Google Scholar 

  28. Andrae, R. Error estimation in astronomy: a guide. Preprint at (2010)

  29. Andrae, R., Schulze-Hartung, T. & Melchior, P. Dos and don’ts of reduced chi-squared. Preprint at (2010)

  30. Kolmogorov, A. Sulla determinazione empirica di una legge di distribuzione. Giornale Istituto Italiano 4, 1–11 (1933)

    Google Scholar 

  31. Smirnov, N. Table for estimating the goodness of fit of empirical distributions. Ann. Math. Stat. 19, 279–281 (1948)

    Article  MathSciNet  Google Scholar 

  32. Davies, A. G., Matson, D., Veeder, G., Johnson, T. & Blaney, D. Post-solidification cooling and the age of Io’s lava flows. Icarus 176, 123–137 (2005)

    Article  ADS  Google Scholar 

  33. Davies, A. G. Io volcanism: thermo-physical models of silicate lava compared with observations of thermal emission. Icarus 124, 45–61 (1996)

    Article  ADS  Google Scholar 

Download references


The Large Binocular Telescope (LBT) is an international collaboration among institutions in the United States, Italy and Germany. The LBT Corporation partners are: the University of Arizona on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; The Ohio State University; and The Research Corporation, on behalf of The University of Notre Dame, University of Minnesota and University of Virginia. The LBT Interferometer is funded by NASA as part of its Exoplanet Exploration program. The LMIRcam instrument is funded by the US NSF through grant NSF AST-0705296. A.G.D., K.d.K. and I.d.P. are partially supported by the NSF grant AST-1313485 to UC Berkeley and by the NSF Graduate Research Fellowship to K.d.K. under grant DGE-1106400. A.G.D. thanks the NASA Outer Planets Research Program for support under grant OPR NNN13D466T.

Author information

Authors and Affiliations



A.C., A.S., D.D., J.L., M.S., P.H., C.V. and C.E.W. developed and operated the instrumentation used to obtain these observations. A.C., A.S., A.V., D.D., E.S., K.d.K., P.H. and V.B. took the data. A.R., J.L. and M.S. performed the data reduction and calibration. K.d.K. and M.S. analysed the data. A.G.D., I.d.P., J.L., K.d.K. and M.S. wrote the main text and the Methods section.

Corresponding author

Correspondence to K. de Kleer.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Additional information

Reviewer Information Nature thanks F. Marchis and J. Spencer for their contribution to the peer review of this work.

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

Extended data figures and tables

Extended Data Figure 1 Io disk subtraction.

a, b, Image of Io from the LBTI during the occultation, both before (a) and after (b) the subtraction of the reflected light from Io’s disk. In each image, Loki Patera is at upper left and Pillan Patera at lower right. The residual intensity around the limb in the subtracted image is the result of imperfect limb darkening correction.

Extended Data Figure 2 Uniform-intensity models.

Main panels, ingress and egress light curves from models with a uniform intensity distribution within Loki Patera, with (bottom row) and without (top row) a central island, plotted with the data and 1σ uncertainties. The patera outline is derived from Voyager imaging data19, and the model light curves in each row correspond to the image in the left panel of that row. It can be clearly seen from a comparison between the rows that the patera shape and the central island produce the broad-scale features of the ingress light curve, even without postulating a non-uniform intensity distribution. However, the addition of a non-uniform intensity distribution is required to match the egress light curve, indicating that the main temperature gradient is in the direction of motion of Europa’s limb during egress (roughly northwest to southeast).

Extended Data Figure 3 Intensity maps corresponding to progressively closer fits.

Shown are intensity reconstructions with independently-fitted pixels sized 8 km × 8 km based on fits to the light curve. The series demonstrates the artefacts from systematic noise in the light curve that become increasingly prominent as the fits tighten. Panels af correspond to Fits A–F discussed in the text. The fit metrics are summarized in Extended Data Table 2; Fit C is the preferred model at this resolution. The arrows at the left show the approximate direction of movement of Europa’s limb during ingress and egress, demonstrating that the orientation of the limb corresponds to the striping artefacts in Fits E and F.

Extended Data Figure 4 Model light curves and residuals.

Shown are model light curves for ingress and egress (with residual plots under) corresponding to the intensity maps for Fits A–F shown in Extended Data Fig. 3, plotted with the observed light curve and 1σ uncertainties (error bars).

Extended Data Figure 5 Preferred models for a range of pixel sizes and two pixel shapes.

The image titles indicate the size of each pixel in kilometres; top row, square pixels; bottom row, diamond pixels. The edges of the diamond pixels are parallel to the limb of Europa as it passes that portion of Loki Patera. Note the artefacts in the small-pixel models with diamond pixel shapes; in these models, as few as two timesteps influence the value of each pixel, and the model is thus very sensitive to noise in the light curve. These images demonstrate that the retrieved intensity distribution is consistent across different model parameters and resolutions. See Methods for details.

Extended Data Figure 6 Retrieval of simulated temperature maps.

The simulated maps (top row) include discrete hot features of Gaussian brightness distribution on top of a uniformly bright background patera. The bright spot constitutes about 15% of the patera’s total intensity in panels ae, and approximately 7.5% of the intensity in panels fh, and ranges in size from 10 km to 40 km (full-width at half-maximum of the feature). The retrieved maps (bottom row) are generated using the same methods applied to the LBT data, based on light curves corresponding to each intensity map with realistic noise added. The figure demonstrates that the presence and location of localized hot features of these brightness levels can be accurately retrieved by the analysis methods, but not their exact shape or size.

Extended Data Figure 7 Retrieval of simulated temperature maps with global gradient.

The simulated maps (a, b) demonstrate two possible models with similar azimuthally smoothed intensity profiles and an overall increase in brightness towards the southeast of the patera. The retrieved maps (c, d) were produced using the same procedure by which the LBT map was produced, based on the simulated light curves (e, f), which include realistic noise. The retrieved maps demonstrate that these scenarios are clearly distinguished by the retrieval process, despite the similarities between the model light curves.

Extended Data Figure 8 Model fits without the central island.

Shown are intensity reconstructions based on light curve fits using models with 8 km × 8 km square pixels, treating the intensity of the pixels in the island as free parameters in the fit. Without making any assumptions about the island, the fits recover its presence. Panels ad demonstrate increasingly tight fits to the light curve; the preferred model on the basis of the corresponding light curve residuals is c here. Panels ad correspond to Fits A–D discussed in the text.

Extended Data Table 1 Observations
Extended Data Table 2 Goodness-of-fit metrics for different models

PowerPoint slides

Rights and permissions

Reprints and Permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

de Kleer, K., Skrutskie, M., Leisenring, J. et al. Multi-phase volcanic resurfacing at Loki Patera on Io. Nature 545, 199–202 (2017).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:

This article is cited by


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


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