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tokens: unavoidable; that is, first-principles numerical simulations that address this plasma regime with adequate separation between the ion and the electron scales may inevitably satisfy the conditions for nonlinear reconnection in turbulent eddies at sub-ion scales. Indeed, the biggest such simulation that we are familiar with reports spectra steeper than in the sub-ion range (Told et al. 2015 ), which could be a manifestation of reconnection-driven energy depletion in the eddies. It is interesting to analyze this result in light of recent MMS observations of so-called electron-only reconnection in the Earth's magnetosheath (Phan et al. 2018 ; Stawarz et al. 2019 ). In Boldyrev Loureiro ( 2019 ) we have estimated that the decoupling of the ions in these events requires or depending on whether one assumes a or magnetic field profile for the reconnecting field in the eddy. These estimates range from ∼6 to ∼12; combined with Equation ( 12 ) or ( 13 ) they suggest a rather narrow range of scales where nonlinear “electron-only” reconnection in the eddies may be possible. Remarkably, Phan et al. ( 2018 ) report a current sheet thickness of , strikingly consistent with these numbers and with Equation ( 12 ). This is certainly very encouraging, but one must also bear in mind that all our analytical results are only order of magnitude estimates which ignore order unity numerical prefactors. Another observationally based result which we interpret to be consistent with our analysis is the recent claim by Chen et al. ( 2019 ) that energy dissipation at kinetic scales in the magnetosheath is dominated by linear electron Landau damping (the energy dissipation rate via that channel being comparable to the energy cascade rate). Indeed, Equation ( 12 ) demonstrates that full reconnection in sub-ion scale eddies is permitted for typical magnetosheath parameters; and previous investigations of heating in (strong guide-field) collisionless reconnection (Loureiro et al. 2013 ; Numata Loureiro 2015 ) show that when β e ≪ 1 linear electron Landau damping is by far the dominant energy dissipation channel. Furthermore, Chen et al. ( 2019 ) report a steepening of the spectrum at the scales where Landau damping is prominent, consistent with our expectations of the effects of active collisionless reconnection in the cascade. 4.3. Low-beta Pair Plasmas For completeness, we address here the case of low-beta pair plasmas, for which governing equations and turbulence scalings are given in Loureiro Boldyrev ( 2018 ). In the MHD regime the same equations as for an electron-ion plasma apply; the discussion is thus unchanged from that of Section 3 . In the case of a collisionless pair plasma, the criterion stated in Equation ( 3 ) yields (exactly as in Equation ( 12 ) since the scaling for γ t is the same). This needs to be reconciled with the requirements for the existence of a tearing range in the first place: for a Harris-type reconnecting profile, these are (Loureiro Boldyrev