By Mike Lockwood (University of Reading)
We have studied the evolution of the debris cloud generated by the high-altitude Anti-Satellite (ASAT) test on the Fengyun-1C satellite over the subsequent 18 years. More of the objects at sizes above 10cm have survived than was predicted four years after the ASAT test, despite the average space weather activity being higher than was assumed in making those predictions. We show how debris accelerated by the test into high-apogee orbits has acted as a reservoir, giving a long-lived supply of objects ready to start the reentry spiral. The average rate of descent varies with the solar cycle and with the solar rotation period because of the variation in EUV heating of the thermosphere. Geomagnetic storms
have a short-lived but significant effect on the altitude decay of the debris, the upper decile of geomagnetic activity accounting for 12% of the lost altitude at 400 km, rising to 19% at 700km. A second, more subtle, geomagnetic effect is seen to be present, identified as being driven by the Russell-McPherron effect on solar wind-magnetosphere couplingand thermospheric heating. The contribution of this mechanism to the semi-annual variation in average debris descent speed is greatest at high altitudes but other thermospheric effects, such as wave and tide dissipation and circulation changes, are more important at lower altitudes. At times of low solar activity the EUV heating is the dominant effect but the total geomagnetic contribution is more significant during disturbed times. We discuss how these results are of importance to controlled de-orbiting of space junk.
References
M. Lockwood, C. J. Scott, J. O'Donoghue, M. J. Owens, and L. A. Barnard (2026)
The contribution of the Russell-McPherron effect to the semiannual variation in thermospheric density, J. geophys. Res. Space Phys., 131, e2025JA034732, doi: 10.1029/2025JA034732
M. Lockwood (2025) The Celestial Rubbish Dump, Astronomy and Geophysics, 66 (3), 3.36–3.42, doi: 10.1093/astrogeo/ataf023
See publication for more details:
M. Lockwood, M.J. Owens, C. Saha, L.A. Barnard, C.J. Scott, and J. O’Donoghue (2026) Space Weather, Submitted

Comparison of days with predominant positive (left) and negative (right) IMF Y-component in the GSEQ frame. Parts A and D show the FY-1C debris descent speed, v, as a function of altitude, h, and fraction of a calendar year, F, where its annual variation due to Sun-Earth distance a (as a function of h) has been subtracted to reveal the semi-annual variation. Parts C and F show the height profiles of (v-a) at the dates of peak Russell-McPherron effect in March (green) and September (mauve). Parts B and E show the variation with F of the average (v-a) over the full height range. The Russell-McPherron effect enhances the March/September peak when the Y-component in GSEQ is negative/positive and so can be clearly seen to be driving a semi-annual variation in debris descent speed at higher altitudes.