Merav Opher                                  Jet Propulsion Laboratory                                  MS 169-506                                  4800 Oak Grove Dr.                                  Pasadena, CA 91109                                  Phone: (818) 393-3251                                  Fax: (818) 354-8895                                  merav.opher@jpl.nasa.gov

The Voyager spacecraft, launched in 77 is the most distant satellite . After more than 20 years, it is now approaching the edge of the solar system. Our goal is to be able to predict, with the greatest accuracy possible, the nature of the physical phenomena created by the magnetic fields of the solar and interstellar media and by the interactions of the plasma and the neutral atoms in this region. In order to model it accurately, it is necessary to use 3D Magnetohydrodynamic calculations. We are using BATS-R-US, a state-of-the-art 3D adaptive grid numerical simulation code, developed at the University of Michigan. With this code, we are able to define physical space with resolutions much better than those previously obtained.
Recently, we found that the current sheet (the region where the solar magnetic field reverses polarity) is unstable (a Kelvin-Helmholtz-like instability) beyond the termination shock. The compressed solar magnetic field at the termination shock slows the solar wind down. In the current-sheet, the plasma passes through a pure hydrodynamic shock, which produces a "jet-sheet". We expect to see this phenomenon in other magnetized, rotating stars.
 

IN THE NEWS:Science Editor's Choice, Science Vol 300, page 2005 (2003)
To an Instability and Beyond

Did Voyager Crossed the Termination Shock? NASA Space Science Update (November 05, 2003)
(part of the panel, with Prof. Ed Stone, Dr. Tom Krimigis and Dr. Frank McDonald) (video in Real Player format)

LATimes article on Voyager (Nov 06, 2003)

NPR Science Friday Nov 13, 2003
 

From 2001-2004 I was a Caltech Postdoctoral Scholar at JPL. My previous post-doctoral experience was working in plasma astrophysics  in the plasma group at UCLA. There I worked with Prof. George Morales, Dr. Jean Noel Leuboff and Prof. John Dawson. Our research involved the study of the effects of electromagnetic fluctuations on nuclear reaction rates. Because the reaction rates are very sensitive to the high energy region of the particle spectrum, they can be affected by distortion of the particle distributions due to electromagnetic fluctuations. This work was a continuation of my Ph.D. investigation of plasma effects in the early Universe, where I studied the effect of the plasma at the epoch when the light elements were formed in the early universe. Generally, many-body effects are assumed to be negligible in cosmological calculations. The universe is treated as a thermal gas of non-interacting particles. However, a plasma is very different from an ideal gas, with collective effects and particle correlations. In general, when collective effects are taken into account in astrophysics, as in stellar interiors, static calculations are used. However, plasma effects have to be analyzed in a dynamic way, treating all the fluctuations in a plasma (not only plasmons and photons), and not just including static screening (Debye-Huckel) in the analysis. For my doctoral thesis, I studied the electromagnetic fluctuations that exist in a plasma, even when it is non-magnetized. I did this study for the epoch of primordial nucleosynthesis, when the universe was formed by an electron-positron plasma, as well as for the period after the annhilation of the electron-positron pairs, when it was an electron-proton plasma. We showed that the electromagnetic spectrum is a blackbody spectrum at high frequencies, but distorted at low frequencies. This shows the importance of collective effects.

My research interests are on the interface between plasma physics, space physics and astrophysics. Near the Sun, as well as in other stellar media, new plasma phenomena can be identified and old theories tested.
 

For a short CV: click here

For cool movies on the Jet Instability: click here