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Earth’s magnetospheric tail could reach the main asteroid belt

Published onJun 01, 2020
Earth’s magnetospheric tail could reach the main asteroid belt

Primitive asteroids 24 Themis (C-B-type, q = 2.7453 AU), 449 Hamburg (C-type, q = 2.1118 AU) and 704 Interamnia (F-B-type, q = 2.5828 AU) were accidentally located at heliocentric distances of 2.76 AU, 2.11 AU, and 3.16 AU, in a narrow angular sector (at phase angles of 17÷25°) and near their perihelion distances (q) on 17-19 March 2019. According to our UBVRI-photometry of these asteroids together with a solar analog star (HIP 29759), they had close in shape interpolated reflectance spectra on 17 and 19 March, with signs of sublimation activity (two peaks at 0.45 µm and 0.65 µm in the spectra pointed to a light-scattering exosphere) (Busarev et al., 2019, 10th Moscow Solar Syst. Sympos., Abs. 10MS3-SW-07). But on March 18 all asteroid reflectance spectra turned out to be very other, without signs of activity, close to the “canonical” ones defined at SMASSII survey. It should be emphasized the UBVRI-data were obtained under good photometric conditions. Such a strange change in the shape of asteroid spectra on March 18 we explained by the effect of sweeping away of a sublimation exosphere by a shock wave in solar wind (SWSW). It may be because of two weak solar flares on March 8-9 (according to data of GOES-15 satellite). The first one (March 8, UT = 03h15m) was more powerful and reached Interamnia on March 18 (middle time of the observation UT = 18h36m38s), as the most distant one, in ~11 days at a speed of ~550 km/s (there were no other solar flares between 9 and 18 March). Perhaps, along with discovering sublimation activity of those asteroids, we could get a new information about solar activity and features of SWSW passing. Interplanetary magnetic field created by the Sun usually spirals all charged particles moving in the anti-solar direction. But we suggest that when the Earth is between the Sun and asteroids, Earth’s magnetospheric tail, stretched in the anti-solar direction, should direct the flowing SWSW nearly in a straight line to asteroids being in opposition. For that a quasineutral charge of the solar wind may also be important. The length of Earth’s magnetotail is still unknown. Based on the above, it can be assumed that it is no less than 2 AU and apparently changes depending on solar activity.

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