Space Sci Rev (2018) 214:58 https://doi.org/10.1007/s11214-018-0485-6 Partially Ionized Plasmas in Astrophysics José Luis Ballester1 · Igor Alexeev2 · Manuel Collados3 · Turlough Downes4 · Robert F. Pfaff5 · Holly Gilbert6 · Maxim Khodachenko7 · Elena Khomenko3 · Ildar F. Shaikhislamov8 · Roberto Soler1 · Enrique Vázquez-Semadeni9 · Teimuraz Zaqarashvili7,10 Received: 29 June 2017 / Accepted: 2 February 2018 © Springer Science+Business Media B.V., part of Springer Nature 2018 Abstract Partially ionized plasmas are found across the Universe in many different as- trophysical environments. They constitute an essential ingredient of the solar atmosphere, molecular clouds, planetary ionospheres and protoplanetary disks, among other environ- ments, and display a richness of physical effects which are not present in fully ionized plasmas. This review provides an overview of the physics of partially ionized plasmas, in- cluding recent advances in different astrophysical areas in which partial ionization plays a B J.L. Ballester
[email protected] I. Alexeev
[email protected] M. Collados
[email protected] T. Downes
[email protected] R.F. Pfaff
[email protected] H. Gilbert
[email protected] M. Khodachenko
[email protected] E. Khomenko
[email protected] I.F. Shaikhislamov
[email protected] R. Soler
[email protected] E. Vázquez-Semadeni
[email protected] T. Zaqarashvili
[email protected] 58 Page 2 of 149 J.L. Ballester et al. fundamental role. We outline outstanding observational and theoretical questions and dis- cuss possible directions for future progress. Keywords Plasmas · Magnetohydrodynamics · Sun · Molecular clouds · Ionospheres · Exoplanets 1 Introduction Plasma pervades the Universe at all scales, and the term plasma universe was coined by Hannes Alfvén to point out the important role played by plasmas across the universe (Alfven 1986).