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Concerns about increasing space debris are prevalent among agencies worldwide. However, scientists from the Indian Space Research Organisation (ISRO) have made a surprising and reassuring discovery. According to a new study by ISRO, the Sun is aiding in the cleanup of space by pulling down old and defunct satellites towards Earth through its activity. Researchers at the Vikram Sarabhai Space Centre (VSSC) have demonstrated for the first time that the Sun's 11-year solar cycle directly affects the altitude of debris in low Earth orbit (LEO).

Their findings, published in 'Frontiers in Astronomy and Space Sciences', could transform how future satellite missions are planned. The research indicates that when solar activity reaches about 67% of its peak during the solar cycle, debris in orbit begins to descend rapidly.

Lead author Aisha M. Ashraf stated, "We show that when the Sun is more active, the space debris around Earth loses altitude much more quickly. For the first time, we found that when solar activity exceeds a certain level, the decrease in altitude occurs significantly faster."

This discovery comes at a crucial time. The low Earth orbit (LEO), which spans approximately 400 km to 2,000 km above Earth, is now congested with satellites, remnants of rockets, and debris from past collisions. This region hosts Earth-monitoring spacecraft and large satellite networks designed for internet connectivity, such as SpaceX's Starlink.

Scientists have warned that even a single collision in orbit could trigger a cascade of debris, creating thousands of fragments that pose risks to operational satellites and future missions.

The team monitored the trajectories of 17 pieces of space debris from the 1960s and tracked their orbital decay over 36 years (during solar cycles 22 to 24). These objects orbit Earth at altitudes between 600 km and 800 km, completing a revolution every 90 to 120 minutes.

Unlike active satellites that adjust their orbits using onboard fuel, space debris responds solely to atmospheric conditions. This characteristic made it ideal for studying how solar activity impacts Earth's upper atmosphere.

When the Sun is highly active, it emits stronger ultraviolet rays and charged particles. These emissions heat and expand the upper layer of Earth's atmosphere, the thermosphere, increasing atmospheric density at orbital heights. This results in greater drag on satellites and debris, causing them to slow down and descend towards Earth.

Researchers correlated the trajectories of debris with long-term solar data, including sunspot counts and measurements of solar radio and extreme ultraviolet emissions, obtained from the German Research Centre for Geosciences in Potsdam. Their analysis revealed a clear "transition threshold" after surpassing about two-thirds of the peak solar activity.

Ashraf noted, "Our results indicate that when solar activity exceeds certain levels, satellites, like space debris, lose altitude rapidly, necessitating more frequent orbital adjustments."

These findings could significantly impact satellite operators, especially as governments and private companies are launching thousands of new spacecraft into already crowded orbits. Missions launched during periods of solar maximum may require more fuel to maintain stability, and changes in debris trajectories could increase collision risks.

Researchers emphasize that this study highlights the unexpected scientific importance of decades-old space debris. Ashraf remarked, "Interestingly, all this information comes from objects launched in the 1960s, and they continue to contribute to science today."