Using plasma physics to weigh the photon

The currently accepted value for the upper bound for the photon mass, m_ph, is 22 orders of magnitude less than the electron mass. As the mass m_ph is so incredibly small, it has essentially no effect on atomic and nuclear physics; and it is very difficult to improve this estimate by laboratory experiments. However, even a very small mass may have a significant effect on astrophysical phenomena occurring on a scale exceeding the photon Compton length (where for the currently accepted mass). A set of magnetohydrodynamic equations (assuming a finite photon mass) are used to analyze properties of the solar wind at Pluto's orbit. This yields an improved (reduced) by a factor of 70 estimate of the photon mass. Possible opportunities and challenges for the further reduction of the upper limit for m_ph based on the properties of larger-scale astrophysical objects are discussed.