Edmond C. Roelof

Publications (12)116.18 Total impact

• Article: No meridional plasma flow in the heliosheath transition region.

  Robert B Decker, Stamatios M Krimigis, Edmond C Roelof, Matthew E Hill
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  ABSTRACT: Over a two-year period, Voyager 1 observed a gradual slowing-down of radial plasma flow in the heliosheath to near-zero velocity after April 2010 at a distance of 113.5 astronomical units from the Sun (1 astronomical unit equals 1.5 × 10(8) kilometres). Voyager 1 was then about 20 astronomical units beyond the shock that terminates the free expansion of the solar wind and was immersed in the heated non-thermal plasma region called the heliosheath. The expectation from contemporary simulations was that the heliosheath plasma would be deflected from radial flow to meridional flow (in solar heliospheric coordinates), which at Voyager 1 would lie mainly on the (locally spherical) surface called the heliopause. This surface is supposed to separate the heliosheath plasma, which is of solar origin, from the interstellar plasma, which is of local Galactic origin. In 2011, the Voyager project began occasional temporary re-orientations of the spacecraft (totalling about 10-25 hours every 2 months) to re-align the Low-Energy Charged Particle instrument on board Voyager 1 so that it could measure meridional flow. Here we report that, contrary to expectations, these observations yielded a meridional flow velocity of +3 ± 11 km s(-1), that is, one consistent with zero within statistical uncertainties.
  Nature 09/2012; 489(7414):124-7. · 36.28 Impact Factor
• Article: Zero outward flow velocity for plasma in a heliosheath transition layer.

  Stamatios M Krimigis, Edmond C Roelof, Robert B Decker, Matthew E Hill
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  ABSTRACT: Voyager 1 has been in the reservoir of energetic ions and electrons that constitutes the heliosheath since it crossed the solar wind termination shock on 16 December 2004 at a distance from the Sun of 94 astronomical units (1 AU = 1.5 × 10(8) km). It is now ∼22 AU past the termination shock crossing. The bulk velocity of the plasma in the radial-transverse plane has been determined using measurements of the anisotropy of the convected energetic ion distribution. Here we report that the radial component of the velocity has been decreasing almost linearly over the past three years, from ∼70 km s(-1) to ∼0 km s(-1), where it has remained for the past eight months. It now seems that Voyager 1 has entered a finite transition layer of zero-radial-velocity plasma flow, indicating that the spacecraft may be close to the heliopause, the border between the heliosheath and the interstellar plasma. The existence of a flow transition layer in the heliosheath contradicts current predictions--generally assumed by conceptual models--of a sharp discontinuity at the heliopause.
  Nature 06/2011; 474(7351):359-61. · 36.28 Impact Factor
• Article: Titan's exosphere and its interaction with Saturn's magnetosphere.

  Iannis Dandouras, Philippe Garnier, Donald G Mitchell, Edmond C Roelof, Pontus C Brandt, Norbert Krupp, Stamatios M Krimigis
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  ABSTRACT: Titan's nitrogen-rich atmosphere is directly bombarded by energetic ions, due to its lack of a significant intrinsic magnetic field. Singly charged energetic ions from Saturn's magnetosphere undergo charge-exchange collisions with neutral atoms in Titan's upper atmosphere, or exosphere, being transformed into energetic neutral atoms (ENAs). The ion and neutral camera, one of the three sensors that comprise the magnetosphere imaging instrument (MIMI) on the Cassini/Huygens mission to Saturn and Titan, images these ENAs like photons, and measures their fluxes and energies. These remote-sensing measurements, combined with the in situ measurements performed in the upper thermosphere and in the exosphere by the ion and neutral mass spectrometer instrument, provide a powerful diagnostic of Titan's exosphere and its interaction with the Kronian magnetosphere. These observations are analysed and some of the exospheric features they reveal are modelled.
  Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences 12/2008; 367(1889):743-52. · 2.77 Impact Factor
• Source

  Available from: jhuapl.edu

  Article: Global imaging of O+ from IMAGE/HENA

  Donald G. Mitchell, Pontus C:son Brandt, Edmond C. Roelof, Douglas C. Hamilton, Kyle C. Retterer, Steven Mende
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  ABSTRACT: The magnetospheric O+ population in the 52–180keV range during storms is investigated through the analysis of energetic neutral atom (ENA) images. The images are obtained from the high energy neutral atom (HENA) imager onboard the IMAGE satellite. At each substorm onset following the commencement of a geomagnetic storm the oxygen ENA display ∼30 min intense bursts. Only very weak corresponding features in the 60–119keV hydrogen ENA can be occasionally seen. The dominating fraction of the oxygen ENA emissions are produced when O+ ions mirror/precipitate at low altitudes, where the number density of the neutral atmosphere is high. During the storm we observed several bursts of oxygen ENA, but it is still not clear how much the O+ content of the ring current increases during the storm main phase. Our observations suggest that the responsible injection mechanism is mass-dependent and scatters the pitch angles. This leads us to favor a non-adiabatic mechanism proposed by (Delcourt, 2002).
  Space Science Reviews 09/2003; 109(1):63-75. · 3.61 Impact Factor
• Article: A nebula of gases from Io surrounding Jupiter.

  Stamatios M Krimigis, Donald G Mitchell, Douglas C Hamilton, Jannis Dandouras, Thomas P Armstrong, Scott J Bolton, Andrew F Cheng, George Gloeckler, K C Hsieh, Edwin P Keath, Norbert Krupp, Andreas Lagg, Louis J Lanzerotti, Stefano Livi, Barry H Mauk, Richard W McEntire, Edmond C Roelof, Berend Wilken, Donald J Williams
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  ABSTRACT: Several planetary missions have reported the presence of substantial numbers of energetic ions and electrons surrounding Jupiter; relativistic electrons are observable up to several astronomical units (au) from the planet. A population of energetic (>30[?]keV) neutral particles also has been reported, but the instrumentation was not able to determine the mass or charge state of the particles, which were subsequently labelled energetic neutral atoms. Although images showing the presence of the trace element sodium were obtained, the source and identity of the neutral atoms---and their overall significance relative to the loss of charged particles from Jupiter's magnetosphere---were unknown. Here we report the discovery by the Cassini spacecraft of a fast (>103[?]km[?]s-1) and hot magnetospheric neutral wind extending more than 0.5[?]au from Jupiter, and the presence of energetic neutral atoms (both hot and cold) that have been accelerated by the electric field in the solar wind. We suggest that these atoms originate in volcanic gases from Io, undergo significant evolution through various electromagnetic interactions, escape Jupiter's magnetosphere and then populate the environment around the planet. Thus a 'nebula' is created that extends outwards over hundreds of jovian radii.
  Nature 02/2002; 415(6875):994-6. · 36.28 Impact Factor
• Article: SPIE's 1996 International Symposium on Optical Science, Engineering, and Instrumentation

  Donald G. Mitchell, Stamatios M. Krimigis, Andrew F. Cheng, Shiew-Luan Hsieh, Stephen E. Jaskulek, Edwin P. Keath, Barry H. Mauk, Richard W. McEntire, Edmond C. Roelof, Charles E. Schlemm, Barry E. Tossman, Donald J. Williams
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  ABSTRACT: The INCA sensor is the first energetic neutral atom (ENA) imager funded for flight by NASA. It is a part of the Magnetrospheric Imaging Instrument (MIMI) on the Cassini mission to Saturn, where it will be well suited to monitoring the global dynamics of the Saturn-Titan magnetospheric system throughout the orbital tour. INCA will perform remote sensing of the magnetospheric energetic ion plasmas by detecting and imaging charge exchange neutrals, created when magnetospheric ions capture electrons from ambient neutral gas. The escaping charge exchange neutrals were detected by the Voyager-1 spacecraft outside Saturn's magnetosphere, and can be used like photons to form images of the emitting regions, as has been done at Earth. Since Cassini is 3-axis oriented, INCA is designed as a 2D imager with a field of view of 90 by 120 degrees. The technique involves sensing the position of the ENA as it penetrates an entrance foil and again ont he back-plane microchannel plate, thereby establishing the ENA's trajectory and time- of-flight. Along with rough composition determined by pulse- height analysis, the sensor produces images of the hot plasma interaction with the cold ambient neutral gas as a function of species and energy, from approximately 20 keV to several MeV. A large geometric factor allows sufficient sensitivity to obtain statistically significant images in approximately 1 to 30 minutes, depending on conditions and location. We will discuss several of the design details unique to this instrument, as well as recent calibration results.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
  10/1996;
• Article: INCA: the ion neutral camera for energetic neutral atom imaging of the Saturnian magnetosphere

  Donald G. Mitchell, Andrew F. Cheng, Stamatios M. Krimigis, Edwin P. Keath, Stephen E. Jaskulek, Barry H. Mauk, Richard W. McEntire, Edmond C. Roelof, Donald J. Williams, Ke C. Hsieh, Virginia A. Drake
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  ABSTRACT: Techniques developed for the detection and characterization of energetic (> 20 keV) ions in space plasmas have been modified to include imaging so that energetic neutral atoms at Saturn may be used to form images of the Saturnian magnetosphere and its interaction with the atmosphere of the moon Titan. The basic elements of the ion-neutral camera head on the magnetospheric imaging instrument for the Cassini mission are described, with emphasis on developmental detection techniques and components. In particular, pulse-height analysis of the microchannel plate responses to different mass neutral is used for rough composition determination, and deflection plates in the aperture as well as time-of-flight measurements allow imaging of neutral atoms from within regions of moderate intensity ambient ion and electron fluxes.
  Optical Engineering 11/1993; 32:3096-3101. · 0.96 Impact Factor
• Article: Instrument requirements for imaging the magnetosphere in extreme-ultraviolet and energetic neutral atoms derived from computer-simulated images

  Edmond C. Roelof, Barry H. Mauk, Robert R. Meier
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  ABSTRACT: Scientific requirements for He(+)(304 A) and energetic neutral atom (ENA) magnetospheric imaging, as well as the derived instrumental requirements are presented. Both ENA imaging of the hot plasma and EUV imaging of the cold plasma are highlighted. The question of the accuracy with which physically significant parameters can be extracted from actual images using computerized algorithms is addressed. An example of an ENA image analyzed by means of the Powell minimization algorithm is given. Automated unfolding of global magnetospheric images is also discussed. A Mercator projection of a model INA image is shown.
  02/1992;
• Article: Energetic neutral atoms: Imaging the magnetospheric ring current

  Edmond C. Roelof
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  ABSTRACT: Magnetospheric imaging is a new discipline whose goal is to make pictures of the energetic particle populations trapped in the magnetic field of Earth (or any other planet). This project demonstrated the technical feasibility and scientific validity of magnetospheric imaging using energetic neutral atoms (ENA) with the publication and quantitative analysis of the first ENA images ever obtained from space. ENA's are produced when singly-charged energetic (approximately 100 keV) trapped ions make an atomic collision with the neutral hydrogen atoms which boil of the top of the Earth's atmosphere. These hydrogen atoms suffuse the entire trapping volume of the magnetosphere. The energetic ion steals the electron from the atmospheric hydrogen, so the energetic ion is transformed into an energetic neutral atom with a velocity of several thousands of kilometers/second. Moreover, the new-born ENA preserves the velocity that the trapped ion had at the time of the collision. Consequently, any population of energetic ions emits ENA's.
  02/1990;
• Article: The terrestrial ring current - From in situ measurements to global images using energetic neutral atoms

  Edmond C. Roelof, Donald J. Williams
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  ABSTRACT: Electrical currents flowing in the equatorial magnetosphere, first inferred from ground-based magnetic disturbances, are carried by trapped energetic ions. Spacecraft measurements have determined the spectrum and composition of those currents, and the newly developed technique of energetic-neutral-atom imaging allows the global dynamics of that entire ion population to be viewed from a single spacecraft.
  07/1988;
• Article: Energetic neutral atom image of a storm-time ring current

  Edmond C. Roelof
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  ABSTRACT: Energetic neutral atom (ENA) images of a storm-time ring current produced from direct measurements and model simulations are presented and analyzed. An ENA image of the storm-time ring current was obtained with the Medium Energy Particles Instrument (MEPI) mounted on ISEE 1 on September 29, 1978, and a zero-order model of the ring current ion was employed to simulate the ENA image. The simulated instrument response is compared with actual ENA measurements. It is observed that the spatial distribution of singly charged ions detected from the ENA images displays equatorial midnight/noon asymmetry in differential ion intensity with a midnight/noon ratio of greater than or equal to 20:1; peak ion fluxs, H(+) and O(+), in the midnight sector are greater than 10 to the 6th/(sq cm s sr keV); and ENA fluxes from the brighter areas of the image exceed greater than 1000/(sq cm s sr keV). It is noted that the ENA image from MEPI data correlates with the morphology of the simulated response of MEPI calculated from the model.
  07/1987;
• Article: Interstellar Probe: Impact of the Voyager and IBEX results on science and strategy

  Ralph L. McNutt Jr, Mike Gruntman, Stamatios M. Krimigis, Edmond C. Roelof, Robert F. Wimmer-Schweingruber
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  ABSTRACT: The ongoing Voyager Interstellar Mission (VIM) and recent observations from the Interstellar Boundary Explorer (IBEX) and Cassini missions are providing significant new information about the interaction of the heliosphere with the very local interstellar medium (VLISM). With new observations have come significant new puzzles for describing the interaction physics. Direct measurements of the shocked, solar-wind flow speed are now possible (from Voyager 2) and show the flow remains supersonic. This is one more piece of evidence supporting the idea that the bulk of the energy density in the plasma resides in a non-thermal component that extends to very high energies. There are both quantitative and qualitative implications for the overall heliospheric structure. Observations of energetic neutral atoms (ENAs) by IBEX (in Earth orbit) from the interaction region(s) of the solar wind and the VLISM show unexpected structure on a variety of scales. In addition to the general “glow” of the sky in ENAs, IBEX data show a relatively narrow “ribbon” of atomic hydrogen emission from ∼200 to ∼6 keV, roughly circular, but asymmetric in intensity, and centered on an ecliptic longitude ∼221 degrees and ecliptic latitude of 39 degrees. The ribbon may be ordered by the interstellar magnetic field. It passes through, rather than being centered on, the “nose” from which the local, neutral interstellar wind enters the Heliosphere, indicating that the flow is not the primary driver of the system as had been thought previously. The neutrals from both the glow and ribbon are also characterized by non-thermal distribution functions. ENAs are observed at higher energies as well by the Ion and Neutral Camera (INCA) on Cassini (in orbit about Saturn). A “belt” of emission, broader than the ribbon but similar to it, is seen up to ∼50 keV. These observations emphasize the need for in situ measurements to understand the global nature of our local galactic environment, which is much more complex than previously thought. Only an interstellar probe with modern instruments and measurement requirements better defined by these recent observations can provide the new information required. Even more importantly, the broader scale of the interaction as revealed in these measurements suggests much greater flexibility in scientifically allowable, asymptotic trajectories from the heliosphere for the probe. This is a significant relaxation in the trajectory requirements that open up the trade space for Jupiter gravity assists to increase the flyout speeds.Highlights► The Voyagers, IBEX, and Cassini are revolutionizing knowledge of the heliosphere. ► The data provides new reason for in situ measurements with modern space instruments. ► An interstellar probe is required to make these measurements. ► This new knowledge also relaxes the technical requirements for such a probe.
  Acta Astronautica. 69:767-776.