Space debris—ranging from defunct satellites and spent rocket stages to fragments resulting from collisions—poses an ever-growing hazard to operational spacecraft and crewed space missions. New investigations reveal that surges in solar activity can hasten the descent of this space junk, thereby altering how scientists forecast satellite lifespans and collision probabilities. The research team’s findings were detailed in the journal Frontiers in Astronomy and Space Sciences.
The Low Earth Orbit (LEO), situated between 400 and 2000 km altitude, is optimal for imaging and surveillance satellites, as well as for internet “mega-constellations.”
Unfortunately, this region is currently cluttered with “trash,” such as debris from obsolete satellites and booster sections, endangering new space launches. For instance, even a single impact can trigger a chain reaction of damage.
Given that robotic missions to actively clear space debris are still in their nascent stages, the current focus for researchers is primarily on achieving more precise tracking of fragments to pinpoint the most perilous objects slated for future removal.
“Here, we demonstrate that the space junk orbiting Earth loses altitude significantly faster when the Sun is more active,” stated Aysha Ashruff from the Vikram Sarabhai Space Centre. “For the first time, we have observed that once solar activity surpasses a specific threshold, the altitude decay accelerates markedly. This observation is anticipated to play a crucial role in planning sustainable space operations moving forward.”
The Sun follows an 11-year cycle of active and quiescent phases, which corresponds with the variation in the number of sunspots and consequently, the intensity of its emitted radiation.
This includes ultraviolet (UV) radiation and charged particles, such as helium nuclei and heavier ions.
When this flow reaches its peak, as it recently did in 2024, solar ejections cause heating and an upward expansion in Earth’s thermosphere (located roughly between 100 and 1000 km, with temperatures ranging from 500 to 2500 degrees Celsius).
This process, in turn, increases the atmospheric density surrounding orbital bodies (at altitudes from 350 to 36,000 km), intensifying drag or “air resistance,” which slows their motion and accelerates their orbital decay.
In their study, Ashraff and her colleagues analyzed the historical trajectories of 17 pieces of LEO space debris over a 36-year span, charting data from the 1960s across solar cycles 22, 24, and 22 (likely a typo, intended for cycles across different periods).
These objects orbit the Earth every 90–120 minutes at altitudes between 600 and 800 km and have not yet entered the atmosphere where they would eventually incinerate.
Since space debris does not execute active station-keeping maneuvers like satellites do, changes in their rate of decay (orbital decrease) are solely dependent on fluctuations in thermospheric density.
“This makes space debris an excellent probe for tracking the long-term influence of solar activity on atmospheric drag,” the researchers noted.
They correlated the trajectories with long-term data from the German Research Centre for Geosciences (GFZ), which monitors sunspot counts and daily variations in solar radio and extreme ultraviolet (EUV) emissions.
The results indicate that once the sunspot count exceeds two-thirds of its maximum value, the space debris passes a “transition boundary”—a threshold beyond which its altitude begins to decrease much more rapidly.
“This threshold level doesn’t seem pegged to a fixed value of solar radiation, but rather to how close the Sun is to the peak of its activity,” Ashruff explained. “Around that point, the Sun emits more intense UV radiation, possibly driven by changes in solar processes that intensify near the maximum.”
The scientists emphasize that their findings are expected to assist space trajectory planners in better scheduling satellite paths to avoid collisions with space debris.
“Our findings show that when solar activity exceeds certain levels, satellites—much like the debris—lose altitude faster, thus requiring more orbital correction maneuvers,” Ashruff added.
This directly impacts the on-orbit longevity of satellites and the amount of propellant they consume, particularly for missions launched near a solar maximum.
“The most fascinating aspect is that all this intelligence comes from objects launched as far back as the 1960s,” Ashruff concluded. “They continue to contribute to science, serving as valuable instruments for studying the long-term consequences of solar activity on the thermosphere.”
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