A team of researchers just chased a pair of reentering satellites in a private jet to learn about the pollution caused by space debris burning up in Earth's atmosphere.
The satellites in question were the European Space Agency's (ESA) Tango and Samba spacecraft, which once formed the Cluster constellation, together with the already de-orbited Rumba and Salsa. The quartet used to study the interaction of Earth's magnetic field with the solar wind. After 25 years of service, ESA took advantage of the Tango and Samba's controlled demise to help scientists learn what happens when satellites break apart and burn up during their spiral back to Earth.
The international team of researchers chased the two reentries, which occurred one day apart — on Aug. 31 and Sept. 1 — above the southern Pacific Ocean a few hundred miles from the Polynesian archipelago of Tonga.
Their goal was to understand what happens when satellites disintegrate and what chemical compounds arise in the process. Although companies such as SpaceX, Amazon and Blue Origin want to launch huge numbers of satellites to space in the next decade — SpaceX alone plans to loft 100,000 of its Starlink V3 spacecraft — very little is known about the effects of satellite reentries on Earth's atmosphere. Researchers are also still unsure which spacecraft burn up completely and how many fragments may reach the ground, putting lives and property at risk.
"We want to understand what happens to these bodies as they fly through the atmosphere, which causes friction and very high temperatures," Jiří Šilha, CEO of the Slovak company Astros Solutions, and one of the researchers aboard the plane, told Space.com. "We know that those satellites break up into fragments, which subsequently melt in the atmosphere."
The researchers chased the reentering spacecraft following exact calculations provided by ESA controllers, who were able to maintain connection with the spacecraft until the very last moment before they plunged into the atmosphere.
The satellite reentries, although they occurred during daylight, were visible from aboard the plane even to the naked eye, said Šilha, and created spectacular fireballs that lasted tens of seconds.
"Bolides and meteors only last a few seconds or less," said Šilha. "But satellites are slower. They enter the atmosphere at a shallower angle, and the atmosphere slows them down further."
But the researchers were there for science, not for a sky show. And it was a rare opportunity: The Cluster trajectories were so precisely known that the scientists could prepare for them and be at the exact spot at the exact time to witness those explosions from only a couple of hundred miles away.
The aircraft, a small commercial business jet, was packed with 30 cameras and spectrometers fitted with special filters to capture not only how the satellites disintegrated but also detect the spectral signatures of the chemical elements released as their bodies burned up.
Eight scientists were squashed on board the darkened jet operating the instruments through the aircraft's six windows as the pilots navigated to the vicinity of the spot where ESA analysts had predicted the breakup would occur.
"We were flying toward the object, and first it looked like a compact source of light as the material ablated," said Šilha. "At some point, there was a sudden explosion as the satellite disintegrated."
The plane allowed the researchers to overcome any clouds that could obscure the view from the ground, and also to bypass the thickest layer of the atmosphere, which would distort the measurements. As the satellites hurtled through the air, slowing down from the mind-boggling speed of 22,370 mph (36,000 kph) at which they hit the upper atmosphere, the jet approached them to within a distance of around 75 miles (120 kilometers).
"We begin observing it when it's at about 90 kilometers [56 miles] and it stops being visible at about 65 to 70 kilometers [40 to 44 miles]," Šilha said. "For about thirty to forty seconds after the explosion, you can observe an interesting structure as all those various fragments ablate in the atmosphere. Then they all either burn up or slow down."
Šilha said the cameras captured tens of fragments, in detail that had never been observed before.
The researchers also attempted to trace seven chemical compounds, including titanium, sodium and potassium, which get released as satellites burn up. The team was especially interested in aluminum, which makes up the majority of a satellite body. Aluminum is not naturally present in Earth's atmosphere and most likely forms aluminum oxide during the incineration. The potential presence of aluminum oxide in the atmosphere in higher concentrations worries scientists, as it could potentially trigger ozone depletion in the stratosphere.
"We tried to measure the aluminum at different altitudes, using specialized filters, which could tell us when this aluminum interacts with the atmosphere," said Šilha. "That's when the aluminum oxide likely forms, and that's something that has never been observed before. We don't know exactly how and in what quantities the aluminum oxide might be forming."
The researchers will now analyze the data to learn exactly what chemical reactions may be occurring during every second of the breakup and burn-up process. The data will help atmospheric physics and chemistry researchers improve their models to further our understanding of the potential damage the growing satellite industry might do to the planet and its climate in the future.
"The data will help us validate whether the models agree with reality," said Šilha.
The team previously chased the reentry of the first of the four Cluster satellites — Salsa — in September 2024. The lessons from that campaign helped the team get closer to the Tango and Samba spacecraft and obtain more and more accurate data.
