A new study finds pollution from satellite megaconstellations could account for 42% of the space sector’s climate impact by 2029.
Satellites are creating a massive pollution problem, according to University College London researchers, who say the growing atmospheric carbon source has a 500 times greater climate impact than ground-based emissions, potentially blocking the Sun.
In a recent paper published in the journal Earth’s Future, researchers demonstrate that satellites are driving a significant rise in upper-atmosphere pollution, raising concerns related to the ongoing climate crisis. By the end of this decade, almost half of this pollution will come from satellite megaconstellations launched since 2019, the researchers claim.
While satellites do emit some exhaust when they engage their thrusters, this is not the primary source of pollution they produce, according to the University College London researchers.
Instead, they point to rocket launches, as they generate a massive amount of carbon soot when discarded rocket bodies and dead satellites burn up on reentry into the Earth’s atmosphere. This carbon is particularly problematic, remaining in the upper atmosphere for an extended period and generating a 500-fold climate impact compared to ground emissions.
The team also investigated other forms of launch-related pollution, noting that chlorine released into the atmosphere by these launches harms the ozone layer, which blocks harmful UV rays; however, this impact is far less severe than the carbon soot. Even projecting out to 2029, the team seems confident that rocket launches, accounting for under a tenth of ozone depletion, and some organizations, such as Blue Origin, will be conducting launches that release no chlorine at all.
This is nonetheless important to monitor, they argue, as China’s space launches typically do release chlorine and are expected to grow in the coming years.
Data for the research were sourced from satellite deployments and rock launches conducted between 2020 and 2022, which found that circulation patterns in the upper atmosphere move very slowly, allowing soot particles to linger for extended periods. In the lower atmosphere, rain and other weather systems remove such particles from car and factory exhaust much more rapidly. With this longer atmospheric life span, each particle in the upper atmosphere has a much greater impact on the environment.
Air pollution from launches and reentry is accumulating in the atmosphere at such a rate that by the end of the decade, it could block as much sunlight as artificial geoengineering projects aimed at reducing global warming. However, the actual cooling effect produced would likely be far below the expected temperature rise due to global warming over the same period, the study authors say.
“The space industry pollution is like a small-scale, unregulated geoengineering experiment that could have many unintended and serious environmental consequences,” said Professor Eloise Marais, the project’s leader and a researcher at UCL Geography. “Currently, the impact on the atmosphere is small, so we still have the chance to act early before it becomes a more serious issue that is harder to reverse or repair. So far, there has been limited effort to effectively regulate this type of pollution.”
Their data indicates that megaconstellations, which the team sees as a significant concern, accounted for 35% of the climate impact of these events, and they expect this to grow to 42% by the end of the decade.
Recent years have seen exponential growth in satellites in near-Earth orbit, primarily driven by the rise of megaconstellations composed of hundreds of thousands of objects. The most well-known of these, SpaceX’s Starlink, accounts for 12,000 individual satellites. Megaconstellations are now consuming over half of the rocket fuel expended, as launches rose from just 114 a year in 2020 to 329 in 2025.
The researchers note that real-world megaconstellation launches between 2023 and 2025 have outpaced their projections based on 2020 to 2022 data, suggesting their predictions may actually underestimate the scale of the problem.
“The cooling effect from the reduction in sunlight that we calculate with our models may sound like a welcome change against the backdrop of global warming, but we need to be extremely cautious,” Professor Marais warned.
“Rocket launches are a unique source of pollution, injecting harmful chemicals directly into the upper layers of the atmosphere and contaminating Earth’s last remaining relatively pristine environment,” lead author Dr. Connor Barker, also with UCL Geography, noted.
“Though this soot’s impact on climate is currently much smaller than other industrial sources, its potency means we need to act before it causes irreparable harm,” Barker says.
The paper, “Radiative Forcing and Ozone Depletion of a Decade of Satellite Megaconstellation Missions,” appeared in Earth’s Future on May 14, 2026.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.
Drifting through the Milky Way may be billions, and on some estimates trillions, of rogue planets: worlds bound to no star, some flung out of the systems where they formed, others perhaps never attached to a star at all. They are also called free-floating, nomad, or starless planets. The reason the figure spans such a wide range is simple. We have confirmed very few of them, and counting things you cannot see is hard.
Microlensing searches have produced fewer than ten likely low-mass free-floating planet detections, according to a survey of the field by IEEE Spectrum. Direct-imaging surveys of young star-forming regions have turned up many more planetary-mass candidates, though their formation history is harder to classify. Almost everything beyond that handful is inference and modelling, and the gap between a small number of firm detections and a projected population in the billions is the real state of play.
A planet with no sun emits almost nothing a telescope can catch directly. The main way these objects are found instead is gravitational microlensing, which does not see the planet at all. It sees what the planet’s gravity does to the light of a star behind it.
When a rogue planet passes almost exactly between Earth and a distant background star, its gravity bends and briefly magnifies that star’s light. The star appears to brighten, then fade, and for a planet-sized lens the whole event is short. The first credible detection of an Earth-mass candidate came this way: an event designated OGLE-2016-BLG-1928, reported in 2020 by Przemek Mróz of the University of Warsaw and colleagues, with a brightening timescale of about 41.5 minutes, the shortest then recorded and only caught because the data were taken at high cadence. The object was estimated at roughly 0.3 Earth masses. It remains a candidate rather than a confirmed rogue, because the data cannot rule out that it sits very far from a host star rather than being truly unbound.
The strength of the method is that it can find low-mass objects nothing else can reach. The weakness is built into it. Each event happens once and never repeats, which makes the mass of any single object hard to pin down, and makes the whole population something you reconstruct statistically rather than observe one by one.
The headline estimates rest mainly on this statistical reconstruction. A 2023 analysis of a nine-year survey by the Microlensing Observations in Astrophysics collaboration, led by Takahiro Sumi at Osaka University, concluded that free-floating planets are far more common than earlier work assumed, and supported the idea that the galaxy holds more such objects than it has stars.
It is worth being clear about what that is. It is not a tally. It is an extrapolation from a small number of brief lensing events, folded through models of how often such events should occur. One NASA-backed estimate puts the Milky Way’s rogue planets at roughly twenty per star, or trillions of worlds in total. Other modelling work lands much lower, closer to one free-floating planet per star over the mass range considered. The honest conclusion is not that anyone has counted them. It is that the population could be enormous, and the uncertainty is still enormous too.
There are two broad accounts of how a planet ends up with no star, and they are not exclusive.
One is ejection. A planet forms in orbit around a star, then gets thrown out, usually by a gravitational shove from a larger planet or a passing star in a crowded cluster. Simulations of dense star-forming regions, such as work modelling the Orion Trapezium cluster at Leiden, produce rogue planets this way in large numbers.
The other is that some of these objects never had a star. They may have formed directly from collapsing gas, the way stars do, but with too little mass to ignite. The International Astronomical Union has suggested the term sub-brown dwarf for objects formed like stars but below the mass needed for fusion, which blurs the line between a small failed star and a large free-floating planet.
A recent wrinkle came from the James Webb Space Telescope. Observing the Orion Nebula, Samuel Pearson and Mark McCaughrean reported around 540 planetary-mass candidates, of which about nine per cent appeared to be in wide pairs, which they nicknamed JuMBOs, for Jupiter-mass binary objects. Pairs are awkward for the ejection story, since it is hard to throw two objects out of a system together and keep them bound to each other. The result is strange enough that it remains contested, with later analyses questioning how many of the pairs hold up and whether the objects should be called planets at all.
The instrument expected to move this from extrapolation toward a census is NASA’s Nancy Grace Roman Space Telescope, now targeted for launch no earlier than September 2026, with a commitment to launch no later than May 2027. Roman will run a dedicated microlensing survey from space, staring at a strip of sky toward the galactic centre for months at a time, above the atmospheric blurring that limits ground-based work.
The expectations have grown as the modelling has improved. An earlier estimate put Roman’s likely haul at around 50 Earth-mass rogue planets. A 2023 study led by Naoki Koshimoto at Osaka University raised that to roughly 400. Japan’s PRIME telescope in South Africa is intended to make simultaneous ground-based observations, which would help measure masses rather than just count events. A 2025 paper by William DeRocco and colleagues, posted to the arXiv, works through how Roman’s data could be used to reconstruct the free-floating planet mass function, the distribution of how many of these worlds exist at each mass.
There is also the prospect of pairing Roman with the European Space Agency’s Euclid, already in orbit. A joint survey, according to BBC Science Focus, could turn up more than 100 rogue planets in its first year.
The useful thing about Roman’s survey is that it has a clear way to be wrong. The models predict hundreds of detections. If Roman finds far fewer, or none, the population estimates and the detection methods both come back under review.
For now the honest position is that rogue planets are real, that a handful have been firmly detected, and that whether they number in the billions or the trillions, and how they mostly form, are open questions a single mission is now built to narrow. The figure to watch is not the trillion. It is the first few hundred, and whether they show up.
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Between 2014 and 2016, the European Space Agency’s Rosetta spacecraft flew alongside Comet 67P/Churyumov-Gerasimenko and analysed the gas streaming off it. The list of compounds it found reads like a catalogue of unpleasant smells: hydrogen sulphide (rotten eggs), ammonia (a horse stable), formaldehyde, hydrogen cyanide (bitter almonds), and several others. In the same gas were molecules that bear on the question of how life began.
Both halves of that are true.
Both are also easy to oversell. The comet would smell foul if you could smell it, and you could not. The chemistry is genuinely interesting without being proof of anything about life’s origins.
The measurements came from an instrument called ROSINA, the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis, led by Kathrin Altwegg at the University of Bern. ROSINA is a pair of mass spectrometers, which sort molecules by mass, not by odour. The “smell” is a translation: a way of describing which compounds were present by naming what they would smell like at a high enough concentration.
In an October 2014 post, the ROSINA team described the mix as rotten eggs from hydrogen sulphide, horse stable from ammonia, a suffocating note of formaldehyde, a faint bitter almond from hydrogen cyanide, alcohol from methanol, vinegar from sulphur dioxide, and a sweet trace of carbon disulphide.
The honest qualifier sits in the same post. These compounds are trace constituents. The bulk of the coma, the cloud of gas around the comet, is water, carbon dioxide and carbon monoxide, all odourless, and the whole thing is so thin it is closer to a vacuum than to any atmosphere you could breathe or smell. The “perfume” is a vivid way to report a mass spectrum, not an experience anyone could have had.
The finding with real weight came later. In 2016, Altwegg and colleagues reported in Science Advances that ROSINA had detected glycine in the comet’s coma, along with phosphorus and two molecules, methylamine and ethylamine, that can act as precursors to glycine.
Glycine is the simplest of the twenty amino acids that make up proteins. Phosphorus is part of the backbone of DNA and RNA and a component of cell membranes. Detecting both around a comet is why this result drew attention, rather than the smell.
The team called it the first unambiguous detection of glycine at a comet. That wording matters. Hints of glycine had appeared before in samples returned from Comet Wild 2 by NASA’s Stardust mission, but because those samples came back to Earth, contamination was difficult to rule out, and the cometary origin had to be argued from carbon isotope ratios. Rosetta measured 67P directly, in space, while flying through the comet’s coma.
The detections were repeated, strongest near the comet’s closest approach to the Sun in August 2015, and correlated with dust, which suggests the glycine was released from icy grains as they warmed. That is what lifted it from “probably cometary” to a direct measurement.
That does not mean the comet carried life. It does not even mean comets created life on Earth. It means a comet preserved and released some of the simple chemical pieces that life uses: an amino acid, a biologically important element, and precursor molecules that point to possible routes for making them.
The finding supports a hypothesis, advocated for decades, that comet and asteroid impacts could have delivered such molecules to the early Earth. The ESA team framed it that way, as comets having the potential to deliver key molecules for prebiotic chemistry. ESA itself flagged the catch in the same breath: a huge evolutionary gap separates delivering ingredients and life taking hold.
One amino acid out of twenty is a long way from a protein, and a protein is a long way from a living cell. The detection narrows the question of where prebiotic molecules could come from. It does not answer how life started, which remains unsolved.
That is enough to be interesting without turning the comet into a frozen seed of biology.
Rosetta ended in September 2016, set down onto 67P in a controlled descent. Its archive is still being worked through, and later analyses have added detections, including phosphorus in solid grains rather than gas.
Rosetta’s comet was not a dirty snowball full of life. It was a cold, ancient body releasing a thin cloud of gas and dust, carrying sulphur compounds, carbon compounds, nitrogen compounds and at least a few molecules that matter for prebiotic chemistry.
The smell line is the hook. The real story is quieter: comets can preserve primitive chemistry for billions of years, then release it when sunlight warms them. Whether that chemistry helped life begin on Earth remains an open question.
Rosetta showed that the raw material was there.
The post When Rosetta sniffed the gas around Comet 67P, it found a cloud that would have smelled of rotten eggs, ammonia and bitter almonds — and hidden in that cosmic stink were some of the chemical ingredients that may have helped life begin on Earth appeared first on Space Daily.
The familiar version goes like this. Early Mars was a warmer world with rivers and lakes and a thick atmosphere. Its internal dynamo died, the planet lost the magnetic field that had shielded it, and the solar wind stripped the air away over billions of years, leaving the cold desert we see now.
The outline is broadly right. The water was real, the dynamo did fail, and the solar wind does strip the atmosphere. But several links in that chain are less settled than the clean telling suggests, and a recent finding shows that not all the missing air went to space.
The strongest part of the story is the water. Dried river valleys, lake beds, deltas and water-formed minerals across the older Martian terrain make it clear that liquid water flowed on the surface, at least intermittently, before roughly 3.5 billion years ago.
That much is not in serious dispute.
Whether the planet was warm is another matter. Keeping early Mars warm is difficult in climate models, because the young Sun was fainter than it is today. One camp argues for a persistently warm and relatively wet climate held up by a dense carbon dioxide atmosphere and extra greenhouse gases. Another argues for a mostly cold and icy planet, frozen for long stretches and warmed only in episodes. The geological and climatological case for a warmer, wetter early Mars has been made in detail, and the cold-and-icy alternative has been modelled just as seriously. The argument has run for decades and is not resolved. “Once warmer” is a reasonable shorthand, but it papers over a real disagreement.
Mars no longer has a global magnetic field, but it clearly had one. The crust carries magnetic imprints locked in when ancient rocks cooled, which means a core dynamo was running early in the planet’s history and then stopped. The usual estimate places the shutdown somewhere between about 4.2 and 3.7 billion years ago, around the same era the atmosphere appears to have thinned.
The timing is not pinned down. Palaeomagnetic work led by Sarah Steele at Harvard, published in Science Advances in 2023, argues the dynamo may have lasted longer and behaved in a more complex way than earlier reconstructions assumed.
The death of the field is real. Exactly when, and how cleanly, is still being worked out.
The clearest evidence comes from NASA’s MAVEN mission, which has orbited Mars since September 2014. MAVEN was built to measure how fast gas escapes the upper atmosphere and what drives it. It found that the solar wind does strip ions from Mars into space, and that the rate jumps sharply during solar storms. A strong storm in March 2015 served as a natural experiment, with escape rates spiking while the spacecraft watched.
Measurements of argon isotopes point the same way. Argon is useful because it is not recycled through rocks and volcanoes the way carbon dioxide is, so its isotope ratio records loss to space fairly directly. On the MAVEN team’s reading, the argon ratio implies that most of Mars’ atmospheric loss happened upward, to space. Carbon dioxide is more complicated, because some of it could also be locked into rocks.
This is the part most often stated too confidently. It is tempting to treat the sequence as simple cause and effect: field on, atmosphere safe; field off, atmosphere gone. The physics is not that tidy.
A planetary magnetic field deflects some of the solar wind, but it can also open channels along which charged particles escape, and in some configurations a field may speed up loss rather than prevent it. Venus is the standing complication. It has no internally generated magnetic field and sits closer to the Sun, yet it holds a dense atmosphere. The match in timing between Mars losing its dynamo and losing its air is suggestive, and the protective reading is the leading one, but the causal claim is not established. Some researchers have argued that a longer-lived dynamo might even have helped Mars lose water rather than save it.
There is also the question of where the carbon dioxide went. If early Mars had a thick carbon dioxide atmosphere, large amounts of carbonate rock should have formed as the gas reacted with water and stone, and for years orbiters did not find nearly enough of it.
In 2025, a team led by Benjamin Tutolo reported in Science that the Curiosity rover had found abundant siderite, an iron carbonate, in the sulphate-rich layers of Gale crater. Scaled across similar deposits, the team estimated the rocks could hold the equivalent of a few to several tens of millibar of atmospheric carbon dioxide. That is a genuine reservoir, and part of the missing inventory, though it falls well short of the roughly one bar thought necessary to warm the surface. Some of the buried carbon also appears to have been released again, which would make it a partial, imbalanced carbon cycle.
So the air left by more than one route. Some was stripped to space, as MAVEN shows is still happening. Some was locked into the crust as rock.
What remains open is the balance between those routes, the true early climate, and how much the dying magnetic field actually mattered. Better palaeomagnetic dating of the dynamo, and missions that sample more of the sulphate layers, are the things likely to narrow it. The cold desert is the settled part. The path it took to get there is still being filled in.
The post Mars was once a warmer world of rivers, lakes and a thicker atmosphere, but after its internal dynamo died and the planet lost the magnetic shield that helps protect an atmosphere, the solar wind stripped much of its air away over billions of years, leaving the cold desert we see today appeared first on Space Daily.
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