A recent study led by Dr. Michael Starkey of the Southwest Research Institute has delivered the first observational evidence from the Magnetospheric Multiscale (MMS) Mission of pickup ions (PUIs) and their related wave activity in the solar wind near Earth.
NASA launched the MMS mission in 2015, deploying four spacecraft to study Earth’s magnetosphere, the magnetic field that protects the planet from harmful solar and cosmic radiation.
Formation and behavior of PUIs
PUIs are created when neutral particles traveling through the heliosphere become ionized by the solar wind. Once ionized, they are carried along with the solar wind and spiral around the local magnetic field, forming a plasma population with properties that differ from the standard solar wind particles.
PUIs displayed a characteristic velocity distribution, without the presence of other significant energetic ion or electron populations. Evidence of wave activity was identified using MMS magnetic field measurements, combined with theoretical predictions of expected wave growth modes based on models of the observed PUIs.
“The results of this study indicate that PUIs can in fact generate waves in the solar wind near Earth and motivate the need for further statistical studies of these processes,” Starkey said. “It may be that PUIs play a larger role in the heating and thermalization of the solar wind near Earth than previously thought, which would have large implications for models of the solar wind throughout the heliosphere.”
