My address:
Prof Dr Juergen Schmidt
University of Oulu
Astronomy Research Unit
PL 3000
FI-90014 Oulu
phone: +358 (0) 504 318 047

I am working as a professor in the Astronomy Research Unit of the University of Oulu. My main research interests are statistical physics and celestial mechanics applied to the dynamics of planetary rings and circumplanetary dust. I am Co-investigator of the Cosmic Dust Analyzer (CDA) instrument onboard the CASSINI (NASA/ESA) mission to Saturn, the Surface Dust Analyzer (SUDA) on the Europa Clipper Mission (NASA), and the JANUS camera onboard the ESA mission JUICE.

Solar System Research

One focus of research are small particles found in the environment of the planets of the solar system (circumplanetary dust). These particles are usually smaller than one millimeter, often only a thousandth or a millionth of millimeter in size. Such particles are widely distributed in the Solar system, often forming ring systems around the gas giants. The grains can be created in a number of different processes. What makes them interesting to study is that they bear information from their points of origin, like the surfaces or even the interiors of the moons of the giant planets. Also, because their motion is affected by the environment of the giant planets, like the presence of magnetic fields or ions and neutral gas, we can learn about this environment from analysing the paths that these particles have taken. Another motivation for the study of dust around the planets is spacecraft hazard: Impacts of larger particles tend to degrade the hardware of spacecraft and in extreme cases may lead to fatal damage.

One example for dust research in Oulu is the Saturnian moon Enceladus (500km diameter).
The CASSINI (NASA/ESA) mission to Saturn has discovered that Enceladus is active, expelling a plume of water vapor and tiny water ice particle from a system of cracks in the ice crust of the moon around its south pole.


The instruments of the CASSINI spacecraft, which is at Saturn until late 2017, have studied Enceladus and its activity in detail. The group in Oulu is involved directly in the science team of the Cosmic Dust Analyzer instrument, which is a detector especially designed for the study of circumplanetary dust. The work characterized the number and sized of the ice grains (Schmidt et al, 2008, Nature), but also their chemical composition (Postberg et al, 2009, Postberg et al, 2011, Nature). This compositional information provided strong evidence that Enceladus harbors a reservoir of liquid water under its surface and the presence of a subsurface ocean was confirmed later by other CASSINI instruments. Further compositional analysis carried out by the Cosmic Dust Analyzer team led to the conclusion on ongoing hydrothermal activity inside Enceladus (Hsu et al, 2015, Nature), possibly in a similar manner as it happens in some places in the deep sea on Earth. This finding bears strong implications for the habitability and the astrobiological potential of the small icy moon Enceladus.

Another example for dust research in Oulu is the ESA funded project "Meteoroid Environment Model for the Jovian System" to assess the dust hazard for ESA's future mission JUICE (JUpiter ICy moons Explorer). In the Jupiter system dust particles are created when fast micro-meteoroids hit the surfaces of the numerous atmosphereless moons of Jupiter. These frequent impacts create small craters and part of the excavated material is ejected into space. Such particles populate then the space around the path of their parent moon and they become visible as a dust ring in images taken at special geometries.


The group in Oulu built a computer model of the Jovian micro-meteoroid environment. It was found that small dust particles form an egg-shaped ring that points towards the Sun, while larger particles form an egg-shaped ring that points away from the Sun (Liu et al, 2016, Journal of Geophysical Research). Some of the particles can slowly change their plane of revolution around Jupiter, so that they eventually revolve even backward around the planet. Part of our research results was covered as a story on the page of the American Geophysical Union (AGU).

We also took part in the investigation of the dust environment of Earth's moon. The analysis of data obtained by the Lunar Dust Experiment (LDEX), onboard the Lunar Atmosphere and Dust Environment Explorer (LADEE) led to the detection of a permanent but variable dust cloud around the moon (Horanyi et al, 2015, Nature).

Another focus of the planetary science group in Oulu are the rings of Saturn. The rings have attracted the attention of prominent researchers and amateur observers in the last three and a half centuries. Today it is known that they consist of a large number of water ice boulders of 10cm to 10m in size. They were discovered by Galileo Galilei and Huygens, Lagrange, Maxwell, and Henon have studied them. One motivation to do so is certainly the spectacular appearance of the Saturnian ring system and the surprising richness of structure and dynamics that it exhibits.

Today we are also interested in understanding the rings because they allow to directly observe processes that were at work in a very similar manner in the early days of the solar system, when the planets formed in a disk around the young Sun.

One example of research is the study of waves that are forming in the rings, manifesting themselves as ripples seen in images and other data taken from spacecraft.

One sort of waves emerges spontaneously from the motion of the ring matter around the planet, in a similar manner as certain waves are excited on the Earth's oceans by winds. Another type of waves is created at certain locations in the rings as a response to the periodically recurring gravitational attraction of Saturnian moons, revolving outside or inside the ring system. Recent work carried out in the group in Oulu (Schmidt et al, 2016, Lehmann et al, 2016, Astrophysical Journal) addressed the way that these waves damp out when propagating away from the location where they are launched.

Other work, carried out in Oulu in the field of planetary rings, is the investigation of how the distribution of particle sizes has established (Brilliantov et al., Proceedings of the National Academy of Sciences, 2015) and how impacts of meteoroids on the rings shatter ring particles, leading to the observation of clouds of shattered material that spreads over the rings (Tiscareno et al, 2013, Science).

Credit: NASA/ESA/JPL , image taken from Tiscareno et al, 20013, Science


NASA Group Achievement Award to the Cassini Cosmic Dust Analyzer Team 2009
Carl Ramsauer Preis 2002 of the Physikalische Gesellschaft zu Berlin

  • M. Lehmann, J. Schmidt, H. Salo
    A Weakly Nonlinear Model for the Damping of Resonantly Forced Density Waves in Dense Planetary Rings Astrophysical Journal, 829
  • J. Schmidt, J.E. Colwell, M. Lehmann, E.A. Marouf, H. Salo, F. Spahn, M.S. Tiscareno
    On the Linear Damping Relation For Density Waves in Saturns Rings Astrophysical Journal, 824
  • X. Liu, M. Sachse, F. Spahn, J. Schmidt
    Dynamics and distribution of Jovian dust ejected from the Galilean satellites Journal of Geophysical Research, Planets, 121
  • A.R. Dzhanoev, J. Schmidt, X. Liu, F. Spahn
    Charging of small grains in a space plasma: Application to Jovian stream particles Astronomy and Astrophysics, 591, A147
  • M. Horanyi, J. Szalay, S. Kempf, J. Schmidt, E. Gruen, R. Srama, Z. Sternovsky
    A permanent, asymmetric dust cloud around the Moon
    Nature, 522, 324
  • N.V. Brilliantov, P.L. Krapivsky, A. Bodrova, F. Spahn, H. Hayakawa, V. Stadnichuk, J. Schmidt
    Size distribution of particles in Saturns rings from aggregation and fragmentation
    Proceedings of the National Academy of Sciences, 112, 9536
  • A.R. Dzhanoev, F. Spahn, V. Yaroshenko, H. Luhr, J. Schmidt
    Secondary electron emission from surfaces with small structure
    Physical Review B, 92, 125430
  • F. Wiederschein, E. Voehringer-Martinez, A. Beinsen, F. Postberg, J. Schmidt, R. Srama, F. Stolz, H. Grubmueller, B. Abel
    Charge Separation and Isolation in Strong Water Droplet Impacts
    Physical Chemistry Chemical Physics, 17, 6858
  • P. Meier, U. Motschmann, J. Schmidt, F. Spahn, T.W. Hill, Y. Dong, G.H. Jones, H. Kriegel
    Modeling the total dust production of Enceladus from stochastic charge equilibrium and simulations
    Planetary and Space Science, 119, 206
  • M. Sachse, J. Schmidt, S. Kempf, F. Spahn
    Correlation between speed and size for ejecta from hypervelocity impacts
    Journal of Geophysical Research, Planets, 120
  • P. Meier, H. Kriegel, U. Motschmann, J. Schmidt, F. Spahn, T.W. Hill, Y. Dong, G.H. Jones
    A Model of the Spatial and Size Distribution of Enceladus Dust Plume
    Planetary and Space Science, 104, 216
  • G. Tobie et al.
    The science goals and mission concept for a future exploration of Titan and Enceladus
    Planetary and Space Science, 104, 59
  • C.S. Arridge et al.
    The science case for an orbital mission to Uranus: Exploring the origins and evolution of ice giant planets
    Planetary and Space Science, 104, 122
  • M. Tiscareno, C. Mitchell, C. Murray, D. Di Nino, M. Hedman, J. Schmidt, J. Burns, J. Cuzzi, C. Porco, K. Beurle, M. Evans
    Observations of Ejecta Clouds Produced by Impacts onto Saturns Rings
    Science, 340, 460
  • A. Bodrova, J. Schmidt, F. Spahn, N. V. Brilliantov
    Adhesion and collisional release of particles in dense planetary rings
    Icarus doi:10.1016/j.icarus.2011.11.011
  • S. Kempf, R. Srama, D. Gruen, A. Mocker, F. Postberg, J. Hillier, M. Horanyi, Z. Sternovsky, B. Abel, A. Beinsen, R. Thissen, J. Schmidt, F. Spahn, N. Altobelli
    Linear high resolution dust mass spectrometer for a mission to the Galilean satellites
    Planetary and Space Science, 65, 10
  • R. Srama et al.
    SARIM PLUS–sample return of comet 67P/CG and of interstellar matter
    Experimental Astronomy, 33, 723
  • F. Postberg, J. Schmidt, J. Hillier, S. Kempf, and R. Srama
    A salt-water reservoir as the source of a compositionally stratified plume on Enceladus
    Nature doi:10.1038/nature10175
  • F. Postberg, E. Gruen, M. Horanyi, S. Kempf, H. Krueger, J. Schmidt, F. Spahn, R. Srama, Z. Sternovsky, M. Trieloff
    Compositional mapping of planetary moons by mass spectrometry of dust ejecta
    PSS 59, 1815
  • S. Kempf, R. Srama, E. Gruen, A. Mocker, F. Postberg, J. Hillier, M. Horanyi, Z. Sternovsky, B. Abel, A. Beinsen, R. Thissen, J. Schmidt, F. Spahn, N. Altobelli
    Linear high resolution dust mass spectrometer for a mission to the Galilean satellites PSS doi:10.1016/j.pss.2011.12.019
  • P. Schenk, D. P. Hamilton, R. E. Johnson, W. B. McKinnon, C. Paranicas, J. Schmidt, M. R. Showalter
    Plasma, plumes and rings: Saturn system dynamics as recorded in global color patterns on its midsize icy satellites
    Icarus doi:10.1016/j.icarus.2010.08.016
  • M. Seiss, F. Spahn and Juergen Schmidt
    Moonlet induced wakes in planetary rings: Analytical model including eccentric orbits of moon and ring particles
    Icarus 210, 298-317
  • J. N. Cuzzi, J. A. Burns, S. Charnoz, R. N. Clark, J. E. Colwell, L. Dones, L. W. Esposito, G. Filacchione, R. G. French, M. M. Hedman, S. Kempf, E. A. Marouf, C. D. Murray, P. D. Nicholson, C. C. Porco, J. Schmidt, M. R. Showalter, L. J. Spilker, J. N. Spitale, R. Srama, M. Sremcevic, M. S. Tiscareno, J. Weiss
    An Evolving View of Saturn's Dynamic Rings
    Science 327, 1470-1475
  • S. Kempf, U. Beckmann, J. Schmidt
    How the Enceladus Dust Plume Feeds Saturn's E ring
    Icarus 206, 446-457
  • H. Salo, J. Schmidt
    N-body Simulations of Viscous Instability of Planetary Rings
    Icarus 206, 390-409
  • J. Schmidt, K. Ohtsuki, N. Rappaport, H. Salo, F. Spahn
    Dynamics of Saturn's Dense Rings
    Chapter 14 in Saturn from Cassini, Springer, 2009, pp 413-458, Dougherty et al. Editors
  • F. Postberg, S. Kempf, J. Schmidt, N. Brilliantov, A. Beinsen, B. Abel, U. Buck, R. Srama
    Sodium Salts in E-Ring Ice Grains from an Ocean Below the Surface of Enceladus
    Nature 459, 1098-1101
  • G. H. Jones, C. S. Arridge , A. J. Coates, G. R. Lewis, S. Kanani, A. Wellbrock, D. T. Young, F. J. Crary, R. L. Tokar, R. J. Wilson, T. W. Hill, R. E. Johnson, D. G. Mitchell, J. Schmidt, S. Kempf, U. Beckmann, C. T. Russell, Y. D. Jia, M. K. Dougherty, J. H. Waite Jr., B. A. Magee
    Fine Jet Structure of Electrically Charged Grains in Enceladus' Plume
    Geophyscial Research Letters 36:L16204
  • Shepelyansky, D.L., Pikovsky, A.S., Schmidt, J., and Spahn, F.
    Synchronization mechanism of sharp edges in rings of Saturn.
    Monthly Notices of the Royal Astronomical Society, 395:1934-1940
  • Schmidt, J., Brilliantov, N. V.
    Aggregation kinetics in a flow: The role of particle-wall collisions.
    European Physical Journal, ST, 171:15-20
2008: 2007: 2006: 2005: before 2004: Conference Proceedings:

Invited Talks
  • Jovian Meteoroid Environment Model JMEM: Dust from the Galilean Satellites, ESAC Madrid, 15 September 2016
  • Dusty Plasma in the Saturn System, COSPAR 2016 Istanbul, 30 July - 7 August 2016 (the whole meeting was eventually canceled)
  • Enceladus' Activity as revealed by Cassini Huygens}, August 2015, 29th General Assembly of the International Astronomical Union, Hawaii
  • Plumes and Jets: Constraints on Vents and Eruption Dynamics from Observations and Models, December 2014, Fall Meeting of the American Geophysical Union
  • Dynamics of planetary rings, Nonequilibrium Dynamics in Astrophysics and Material Science October 31 - November 3, 2011, Yukawa Institute, Kyoto, Japan
  • Dynamics of Enceladus' Plume Particles and the Compositional Profile of the Plume, EPSC-DPS 2011 Nantes, 02-07 October 2011
  • Saturns geheimnisvoller Eismond Enceladus, Lange Nacht der Wissenschaften Berlin-Potsdam, 18. Mai 2011
  • Circumplanetary Dust Rings, COSPAR 2010 Bremen, 18-24 July 2010
  • The Enceladus Dust Plume: Observations and Scenarios for Particle Formation, Dusty Visions Goettingen, 14-16 July 2010
  • Cassini: Bei den Monden des Saturn, Lange Nacht der Wissenschaften Berlin-Potsdam, 5. Juni 2010
  • How the Enceladus dust plume feeds Saturn's E ring, EGU Congress in Vienna, May 7 2010
  • The Icy Breath of the Giant: Ice Particles from Saturn's Active Moon Enceladus, Max-Planck Institute for Dynamics and Self-Organization, Dynamics of Complex Fluids, Goettingen, April 22, 2010
  • Die Staubringe der Gasriesen, Bruno H. Buergel Sternwarte Berlin, Feb 13, 2010
  • Saturns geheimnisvoller Eismond Enceladus, Lange Nacht der Wissenschaften Berlin-Potsdam, 13. Juni 2009
  • Saturns geheimnisvoller Eismond Enceladus, Urania Berlin, Jan 22, 2009
  • Geysers and Plumes on Enceladus, 2nd ISSI-Europlanet Workshop `Moons of the Outer Solar System: Exchange Processes Involving the Interiors', Nov 17-27, 2008, Bern
  • The Icy Breath of the Giant: Formation and Dynamics of Icy Grains in Enceladus' Plume, University of Leicester, Nov 14 2008
  • Propeller Structure Induced in Saturn's Rings by Embedded Moonlets, Nov 10, 2008, DAMTP Astrophysical Fluids Seminar, University of Cambridge, UK
  • Saturn's Main Rings: A Dense Granular System, Conference "Granular Gases Beyond the Dilute Limit", Sept. 7-12, 2008, Bayreuth, Germany
  • The Dynamics of Saturn's Dense Rings, Symposium Saturn After Cassini-Huygens, 28th July- 1st August 2008, Imperial College, London, UK
  • Viscous Overstability in Saturn's Rings, 23rd July 2008, Laboratoire de Radioastronomie ENS, Paris
  • Structure in Saturn's Rings: Modelling and Cassini Data, June 2008, Kolloquium of the SFB "Complex Systems" at the Fritz Haber Institute, Berlin
  • The Formation of Enceladus' Dust Plume, June 2008, AOGS Meeting in Busan, Korea, Session "Outer Planets and Satellites with an Athmosphere"
  • The Dynamics of Saturn's Dense Rings, January 2008, Saturn After Cassini-Huygens Meeting, Pasadena
  • Modelling Cassini Data of Saturn's Rings, 15. January 2008, Nonlinear Dynamics Seminar, University of Bayreuth
  • Cassini am Saturn, 14. Dez. 2007, Public Presentation at the Buergel Sternwarte, Berlin
  • Moonlets Embedded in Saturn's Rings, 2007, Planetenseminar des Deutschen Luft und Raumfahrtzentrums, Adlershof, Berlin
  • Cassini Dust Measurements at Enceladus, Okt. 2005, Department of Astronomy, University of Oulu, Finland
  • Cassini CDA Dust Measurements at Enceladus, 09. Nov. 2005, Planetenseminar des Deutschen Luft und Raumfahrtzentrums, Adlershof, Berlin

Organization of Workshops and Conference Sessions