Scientists have figured out why space debris is falling to Earth

This is important for predicting satellite and space debris collisions: the more accurately experts understand how the orbit of debris changes, the better manoeuvres of operational vehicles can be planned.

Details

The Sun goes through a roughly 11-year cycle of activity. When activity increases, the number of sunspots increases, and with it, the fluxes of ultraviolet radiation and charged particles increase. These heat up the Earth's upper atmosphere, the thermosphere.

Because of the heating, the thermosphere expands upwards. At orbital altitudes, the atmosphere becomes denser than normal and begins to drag satellites and debris harder. This resistance is called atmospheric drag - it slows down an object, causing it to lose altitude and gradually approach Earth.

In the new study, scientists analysed the motion of 17 space debris objects in low Earth orbit. The data spanned 36 years and three solar cycles - the 22nd, 23rd and 24th. The objects were at about 600-800 kilometres altitude and made a revolution around the Earth in 90-120 minutes.

Space debris is convenient for such calculations because it does not perform active manoeuvres like working satellites. Therefore, changes in its orbit better reflect the influence of external factors - primarily the density of the upper atmosphere and solar activity.

Scientists compared the orbits of debris with the number of sunspots and the index F10.7, which is used as an indicator of solar activity. It turned out that the rate of orbital decline increases dramatically when the Sun's activity approaches about two-thirds of its maximum in a cycle.

Why it matters

Low Earth orbit is used by surveillance, communications and Internet satellites. But it's also home to a large number of old vehicles, rocket parts, and other fragments. Even a single collision could generate new debris and increase the risk to other satellites. The European Space Agency has previously warned that the amount of space debris could continue to grow even without new launches if fragmentation creates more debris than manages to fall out of orbit naturally.

The new work helps to calculate more accurately when debris will come down faster, and so better predict dangerous approaches. This is also important for active satellites: during high solar activity, they may need more orbit corrections and more fuel.

At the same time, the active Sun does not "clean" the orbit instantly. It is not that all the debris falls to Earth at once, but that the resistance of the upper atmosphere increases, and objects gradually lose altitude faster.

Background

Most space debris burns up upon re-entry into the atmosphere. But large fragments can partially reach the surface, so the issue of tracking falling objects is becoming more and more urgent. Separate studies have already proposed even using networks of seismometers to track sound waves from debris entering the atmosphere.

The new study concerns an earlier stage - not the moment of impact, but the long orbital descent. It shows that the solar cycle needs to be taken into account when predicting the movement of space debris and planning satellite missions.

Source

The study Characterizing Solar Cycle Influence on Long-Term Orbital Deterioration of Low-Earth Orbiting Space Debris is published in Frontiers in Astronomy and Space Sciences in 2026. The authors studied the influence of solar cycles on the orbital reduction of 17 space debris objects in low-Earth orbit.