Newly Discovered Particles in Solar Wind May Force Rethink of Space Weather Models
WASHINGTON – A new study utilizing data from NASA’s Magnetospheric Multiscale (MMS) mission suggests that previously underestimated particles in the solar wind – known as Pick-Up Ions (PUIs) – may be generating waves that substantially impact the heating and behavior of the space habitat around Earth. The findings, published May 25, 2024, in the Journal of Geophysical Research: Space physics, could necessitate updates to current models of the solar wind and its influence throughout the heliosphere.
Launched in 2015, the MMS mission deployed four spacecraft to investigate Earth’s magnetosphere, the protective magnetic bubble shielding the planet from harmful solar and cosmic radiation.Researchers, led by Michael J. Starkey, analyzed MMS magnetic field measurements and found evidence of wave activity correlated with the presence of PUIs.
PUIs are formed when neutral particles traveling through the heliosphere become ionized by the solar wind, then spiral around the local magnetic field, creating a plasma population distinct from standard solar wind particles. The study revealed a characteristic velocity distribution of thes PUIs, observed without other notable energetic ion or electron populations.
“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 might potentially 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.”
While the research team persistent the waves where likely generated by helium and/or hydrogen PUIs,instrument limitations prevented them from identifying the precise ion species responsible. They modeled the individual ion components – solar wind and PUIs – to pinpoint potential wave generators.
The implications of this revelation extend beyond Earth’s immediate vicinity. as distance from the Sun increases, the density of PUIs in the solar wind also rises, possibly increasing their contribution to wave-particle interactions and the overall heating of the solar wind. At the outer edges of the solar system, PUIs already contribute significantly to the total dynamic pressure in the solar wind, impacting processes at the termination shock and in the heliosheath.
“Near Earth, the intensity of PUIs is relatively low, and so it is typically assumed that their contribution to wave-particle interactions in the solar wind is negligible,” Starkey added.”If this assumption is false, current theory and modeling of the solar wind and its evolution throughout the heliosphere would need to be updated.”
The study, titled “First MMS Observations of Waves Possibly Generated by PUIs Near Earth,” is available with DOI: 10.1029/2024JA033660.