Rocket debris that has been drifting in low Earth orbit since the 1960s just helped scientists find something they had missed for decades — a specific threshold in solar activity past which space junk starts falling toward Earth measurably faster

Rocket debris that has been drifting in low Earth orbit since the 1960s just helped scientists find something they had missed for decades — a specific threshold in solar activity past which space junk starts falling toward Earth measurably faster

Spent rocket stages and defunct satellites do not manoeuvre. Once launched, they simply fall, very slowly, pulled toward Earth by the drag of an upper atmosphere that thickens and thins with the Sun’s eleven-year activity cycle. That passivity makes them useful. Because they never fire a thruster to correct their orbit, every metre of altitude lost is a direct record of the air pushing against them, and through that, a record of the thermosphere…