Betatron Cooling of Electrons in Martian Magnetotail

Abstract

Betatron cooling, a plasma process losing particle energy in the perpendicular direction but reserving particle energy in the field‐aligned direction, is a consequence of magnetic depression under the conservation of magnetic moment. Such process has been widely studied in the Earth's magnetosphere but has never been reported in other planetary environment. Here, by utilizing the Mars Atmosphere and Volatile EvolutioN (MAVEN) measurements, we report two events of betatron cooling in the Martian magnetotail. In one of the events, betatron cooling occurs in the suprathermal and energetic ranges of electrons, whereas in the other event, it occurs in the thermal‐energy range. We quantitatively reproduce these two processes by using an analytical model. Gratifyingly, the cooling factor derived from the analytical model agrees well with the observation of magnetic depression. These results, for the first time demonstrating the betatron‐cooling effect beyond the Earth, are useful to understand the electron dynamics in the planetary magnetosphere.

Retracted: New Types of Electron Pitch Angle Distributions on Mars: Funnel and Skirt Distributions

“…The two-sided conic, also termed bidirectional electron conic or butterfly PADs, showing electron pitch angles around 𝐴𝐴 45 • and 𝐴𝐴 135 • , has been observed on the nightside as well as near strong crustal magnetic anomalies (e.g., Cao et al, 2020;Ulusen et al, 2011). Additionally, the double field-aligned beam, also termed cigar PADs, showing electron pitch angles around 0° and 180°, has been observed and proved that betatron cooling is one of the causes of such distributions in Martian magnetotail (e.g., Guo, Fu, Cao, Fan, et al, 2021). Even more to the point, the pancake, isotropic, butterfly, cigar distributions have been well studied on Earth (e.g., Chen et al, 2019;Fu, Chen, et al, 2020;Fu, Xu, et al, 2019;Fu, Zhao, et al, 2020;H.…”

“…In addition, the corresponding omnidirectional electron distribution function of Case‐1 is shown in Figure 3c. We are able to fit these PSDs by using a Maxwellian distribution and two power‐law distributions (e.g., Fu, Grigorenko, et al., 2020; Fu, Peng, et al., 2019, Guo, Fu, Cao, Fan, et al., 2021; Zhao et al., 2019). Quantitatively, the Maxwellian distribution is $$PSD\propto {N}_{e}{\left(\frac{1}{2\pi k{T}_{e}}\right)}^{\sfrac{3}{2}}\,\mathrm{exp}\left(\frac{{-E}_{e}}{k{T}_{e}}\right)$$ with $${N}_{e}=30\,{cm}^{-3}$$ and $${T}_{e}=5.2\,eV$$ (see the blue dashed line in Figure 3c), which describes the 3–50 eV electrons well; the first power‐law distribution is $$PSD\propto {{E}_{e}}^{-\gamma }$$ with $$\gamma =3.64$$ (see the purple dashed line in Figure 3c), which describes the 50–800 eV electrons well; the second power‐law distribution is $$PSD\propto {{E}_{e}}^{-\gamma }$$ with $$\gamma =2.14$$ (see the red dashed line in Figure 3c), which describes the 0.8–5 keV electrons well.…”

MAVEN Observations of Tailward Reconnection Front in the Martian Magnetotail

“…(2011) and Guo et al. (2021). The source of electrons is selected in the time interval between 07:50:35 and 07:50:40 UT which is omnidirectional and is close to the TRF (solid lines in Figure 4a) and the consequence of electron is selected in the time interval between 07:50:40 and 07:50:42 UT (solid lines in Figure 4b).…”

First Observation of Lower Hybrid Drift Waves at the Edge of the Current Sheet in the Martian Magnetotail

“…The Martian magnetotail is extremely complex and active, populated by a variety of field structures (e.g., Brain et al 2007;Xu et al 2017;Guo et al 2021a) that facilitate the transport of mass, momentum, and energy through an assortment of processes, such as magnetic reconnection (e.g., Halekas et al 2009;Harada et al 2015a), flux rope evolution (e.g., DiBraccio et al 2015;Hara et al 2017), and current sheet flapping (DiBraccio et al 2017), etc. Moreover, the Martian plasma sheet, filling with planetary ions, has been identified as a main ion escape channel (e.g., Fedorov et al 2006;Barabash et al 2007;Dubinin et al 2011;Dong et al 2015) due to tailward plasma flows (e.g., Dubinin et al 2012;Harada et al 2015b;Halekas et al 2016;Inui et al 2018).…”