A new study has found that when the Sun is more active, space debris around the Earth loses altitude much faster, which could help with planning future space operations.
Old satellite debris and rocket parts litter the atmosphere. With over 140 million objects orbiting the Earth at an average of ten times the speed of a bullet, space junk poses a significant risk to new satellites and communication constellations, as well as new space launches, like the recent Artemis II mission. Any collision can cause massive damage and generates more debris, meaning the issue is only getting worse over time.
There have been a variety of solutions posed to reduce the amount of space junk, from robots that will capture the debris to using ion beams to bring junk into the Earth’s lower atmosphere, where it burns up upon descent.
But planning these missions still requires navigating the debris to prevent collisions, which have proven difficult to predict- until now.
Brighter, hotter, faster, heavier
A new study in Frontiers in Astronomy and Space Sciences examined 36 years of space junk data and when contrasted with solar activity records, observed that peak activity on the Sun correlated with declining orbits.
The Sun emits UV radiation and charged particles, like helium nuclei and heavy ions, across an 11-year cycle of active and quiet phases, which correlates with the number of sunspots. When the solar emissions peak, as they did most recently in late 2024, the heat reaches the Earth’s thermosphere(located between approximately 100 and 1,000 km, with a temperature between 500 and 2,500 °C) and increases atmospheric density, which increases the drag on objects in orbit. This increased resistance slows the space debris down and makes it fall to Earth faster.
The team followed the historic trajectory of 17 LEO space junk objects over a 36-year period since the 1960s, during the 22nd through 24th solar cycles and cross-referenced the data with long-term data at the German Research Centre for Geosciences in Potsdam.
“Here we show that space debris around Earth loses altitude much faster when the Sun is more active,” said author Ayisha M Ashruf, a scientist and engineer at the Space Physics Laboratory, Vikram Sarabhai Space Centre, Thiruvananthapuram, India.
A threshold boundary to determine when space debris is more likely to fall is when the number of sunspots exceeds two-thirds of its maximum – what the paper calls the ‘transition boundary’.
“This threshold doesn’t seem to be tied to a fixed value of solar radiation, but rather to how close the Sun is to its peak activity. Around this point, the Sun produces more intense EUV radiation, which may be driven by changes in solar processes that become stronger near the peak,” concluded Ayisha Ashruf.
Space weather is crucial to forecasting space junk movement
Space junk obviously lacks the ability to course-correct or manoeuvre like satellites, so being able to utilise thermospheric density fluctuation data could be essential to planning collision-free trajectories for future space missions.
“Our results imply that when solar activity passes certain levels, satellites – just like space junk – lose altitude faster so that more orbit corrections are required. This directly affects how long satellites stay in orbit and how much fuel they need, especially for missions launched near a solar maximum,” explained Ayisha Ashruf.
“What is most interesting is that all of this information comes from objects launched back in the 1960s. They are still contributing to science, serving as valuable tools for studying long-term effects of solar activity on the thermosphere.