Astronomers are sounding the alarm about low-Earth orbit satellites and space debris as significant contributors to light pollution that will affect even the remotest earthbound stargazer.

Starlink map
More than 3,500 Starlink satellites are currently in orbit.

Anyone who has watched the night sky recently knows it: Satellites are everywhere. They flash across the firmament, paint streaks on photos, and irritate stargazers. In just three years since the advent of so-called megaconstellations, such as SpaceX’s Starlink, light pollution by objects in Earth’s orbit has moved from non-topic to possibly the most serious threat to ground-based astronomy. And, as John Barentine (Dark Sky Consulting) and his colleagues discuss in a paper published in Nature Astronomy, it could get worse — much worse.

“We fear that faint astrophysical signals will become increasingly lost in the noise due to satellite megaconstellations,” the team writes. The hunt for potentially dangerous near-Earth asteroids (NEAs) is one possible victim of orbital overkill: “Hazardous near-Earth objects that sky surveys may fail to detect often first appear in our skies in the twilight hours around sunset and sunrise, times when satellites and space debris are most likely to interfere with observations.”

As if to prove their point, a Japanese lunar probe named EQUULEUS fooled NEA-hunters just last week, causing astronomers to waste time on follow-up observations before they figured out what they were looking at. 

No Escape

Satellites don’t shine on their own. They reflect sunlight as they circle our planet. Depending on size, design, orbital height, and solar depression (how low the Sun sinks below the horizon), they may be more or less bright, appearing as moving “stars” to an observer on the ground. Some of them rival the brightest stars, but even the ones invisible to the unaided eye cause streaks on astronomical images. In summer season, they bother high-latitude observers all night; during winter and closer to the equator, satellites are more visible toward dusk and dawn.

Since 2019, the number of functional satellites in low-Earth orbit has more than doubled. But the real problem lies in the near future: Plans to launch up to 100,000 more within just a few years are well underway.

Satellites are more than just annoying moving dots. In 2021, Miroslav Kocifaj (Slovak Academy of Sciences) and colleagues estimate in the Monthly Notices of the Royal Astronomical Society that the accumulated light reflected by all large and small space objects has already made the night sky at zenith up to 10% brighter than it was at the beginning of the Space Age. This is true world-wide, even in remote places where ground-based light pollution is absent. There is no escape from space-based light pollution.

Given this projection, Barentine’s team expects that by 2030 the night sky at zenith will be at least 12% brighter as compared to a natural dark sky, counting the effects of both intact satellites and debris. And in fact, debris have the most impact. “Recent work confirmed that intact satellites will only add about 1% to the diffuse brightness of the zenith,” Barentine adds.

It’s the Debris

Debris pictured in low-earth orbit
This artist's impression shows the debris in low-Earth orbit; while based on data from 2008, the size of individual debris is not to scale.

In the January 2022 Astronomy & Astrophysics, Cees Bassa (Netherlands Institute for Radio Astronomy) and others argued that small debris fragments are having the greatest effect on sky brightness: "The macroscopic satellites composing the constellations . . . will not contribute much to the diffuse sky brightness provided they are not ground into microscopic debris.”  Space debris, however, has the potential to seriously brighten our night sky globally for decades and even centuries to come.

Space debris is anything human-made in orbit that isn’t a working piece of technology: retired or broken satellites, leftover rocket stages, satellite parts and tiny pieces from collisions. The European Space Agency (ESA) estimates that, as of December 2022, some 36,500 objects larger than 10 cm orbit Earth. Smaller objects are harder to track, and their number more difficult to estimate. ESA believes that there could be up to 1 million pieces large enough to seriously damage working satellites in orbit, and 130 million smaller ones down to 1 mm.

So far, space-debris has mostly been a concern for satellite operators, as even cm-size particles in orbit can carry enough kinetic energy to damage or destroy satellites. But these fragments, too, reflect sunlight, albeit only a tiny amount each, so their accumulated light increases the overall brightness of the night sky.

By how much depends on how frequently the many, many satellites to be launched will collide with each other. Such catastrophic events, whether accidental or intentional, create huge clouds of debris, which can in turn cause more collisions.

In a densely populated environment, with hundreds of thousands of satellites of competing enterprises sharing similar orbital altitudes, any one collision could lead to a cascade effect that will not only render certain orbits useless for satellite operation, but will also change our night skies for generations to come. In the latter calculation, even small debris may have a significant impact due to their sheer number.

If too many debris-generating events occur, Bortle 1 skies — already rare on our planet — could be practically impossible to find except in deep winter nights at very remote locations. For professional astronomy, Barentine’s team concludes, losing darkness even at remote sites translates to higher cost to achieve certain scientific goals. As night sky brightness rises, they write, the exposure time required to reach any particular signal-to-noise ratio increases concomitantly.

The Solution: Fewer Satellites

So far, some companies have attempted to reduce the reflectivity of their satellites, and astronomers have worked on algorithms to remove satellite streaks from their data. But these strategies, Barentine’s team writes, have had only limited effect. For example, SpaceX’s “DarkSat” and “VisorSat” designs failed to reduce Starlink brightness below naked-eye visibility, and both designs were ultimately abandoned for engineering reasons. Correction methods may help clean up astronomical images but will not be able to recover all the data. Most importantly, none of these strategies remedy the debris problem.

“Perhaps the mitigation option least palatable to the commercial space industry, but one that governments may certainly impose, is to simply launch fewer satellites into near-Earth space,” the researchers conclude. In the end, they write, restrictions of objects allowed at certain altitudes may be the only way forward for sustainable space.


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B l a k s t a r

March 27, 2023 at 8:52 am

‘Twas ever thu$ with these homo sapiens. Sad.

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March 27, 2023 at 10:49 am

Should coat them with Vantablack whenever possible. That would cut down on reflections a lot although it might lead to overheating.

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March 27, 2023 at 12:38 pm

There are two obvious solutions, but I'll say them anyway.
Don't subscribe to these services.
Support non-satellite communication solutions.

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David Oesper

March 28, 2023 at 2:36 am

This situation illustrates yet another reason why we need binding international laws that apply to all nations and are enforced by a global authority. Individual nations will have to give up some sovereignty in order to effectively address global threats such as nuclear weapons, warfare, human rights violations, pandemics, climate change, pollution, environmental degradation, loss of biodiversity, and, yes, satellite constellations. Whether the United Nations can be strengthened to serve in this role or a new organization created needs to be explored.

The solution to the satellite constellation problem? Fly a small number of internationally-managed constellations of global broadband internet satellites, and require companies and nations to utilize them, similar to the co-location often required for terrestrial communication towers.

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April 1, 2023 at 3:13 pm

I am a 75 year old long time astro-photographer. I have been sounding the alarm on this for some time but I am disgusted at the lack of strong complaints from the scientific community. The CEO of Tesla brushes this issue off by saying that ground based telescopes aren't needed anymore as they are much more effective in space. He failed to mention the cost to put a HST or WST up and the limited accessibility of those telescopes to most scientists. And how about all the public tax money that was spent for these soon to be obsolete or severely neutered observatories.

At one time the most dangerous part of a trip to space was the take off or re-entry. I have heard that now the danger of bing in orbit and hitting space debris is more dangerous.

I wonder how much of this was made possible by putting money in the pockets of those who make decisions in poliics. The old adage probably is true.....

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April 1, 2023 at 10:14 pm

Speaking as a telecommunications engineer, I work regularly within the framework of the ITU (International Telecommunication Union). The ITU is a worldwide organization of 193 countries whose mission is international cooperation in the use of the electromagnetic radio spectrum. In general, artificial Earth satellites are "coordinated" through the ITU. Regular summits are held to address interference issues and re-assignment of the EM Spectrum to accommodate new technologies. Generally, it works very well as it is in the best interests of all nations involved to cooperate.

Unfortunately, not every nation is a member...most notably Communist China. The PRC is also not signatory to the international agreements prohibiting the militarization of space. Where there are totalitarian dictatorships, the can be no binding international laws. Unfortunately, the UN is an impotent organization that is often used as a podium for miscreant nations. Where there are dictators, there will be war, human rights violations, pandemics, pollution, etc. Those are the facts of international relations. I wish it were different.
Terrestrial communication towers are sited via engineering studies in coordination with the FCC and the FAA.and most onerously...zoning boards. Technologically, the devil is in the details. Unfortunately, a small number of LEO satellites won't do the job.

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Anthony Barreiro

April 4, 2023 at 2:19 pm

Do I understand your comment correctly? In your professional opinion, we have no choice but to enshroud the Earth with a miasma of satellites, sacrificing our ability to see the rest of the universe so we can more quickly and easily share TikTok videos?

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March 29, 2023 at 10:55 am

SpaceX is using a reflective surface on their Gen 2 Starlink satellites to divert sunlight away from observers on the ground. They are also orienting the spacecraft body and solar panels to minimize brightness.

The effectiveness of this new approach will be evident from magnitudes that are being recorded by amateur astronomers. There are instructions for visual observers wishing to contribute to this effort here:

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April 1, 2023 at 3:24 pm

While efforts such as the one Anthony-Mallama wrote about sounds like something is being done, we need to act now. All that data gathering would be better spent fighting this pollution with strong protests and astro scientists making their voices strong. I am afraid that once that data comes in....the damage will have already been done. Don't shut the bard door after the horses are already gone.

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Anthony Barreiro

April 1, 2023 at 6:28 pm

"Gather data or protest" is a false choice. We need to do both. Protests supported by clear and convincing data are generally more successful than those based on cranky anecdotes.

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April 5, 2023 at 10:20 am

Anthony – Thank you for correcting the misinformation posted by RKBerta. Professional and amateur astronomers all over the world are observing artificial satellites. This work is essential for protecting dark skies.

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Anthony Barreiro

March 29, 2023 at 7:24 pm

This is the tragedy of the commons on the grandest scale we humans have achieved. I'm afraid that most people, including political authorities, won't even be aware of this problem until it is too late to do anything about it. International regulation is the only solution. As David Oesper commented above, one global satellite network would be better than multiple jostling herds of satellites in the LEO wild west.

As Joni Mitchell sang: "Don't it always seem to go that you don't know what you've got 'til it's gone. They paved paradise and put up a parking lot."

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March 31, 2023 at 7:54 pm

Earth is a lost cause.

Efforts should be directed at keeping the Moon pristine permanently. Right now the far side of the Moon is the best place in the Earth-Moon system for large optical and radio telescope facilities that's half way accessible.

However, I recently heard someone's planning on putting up a 4G network to facilitate communications there, which presumably means mucking up the lunar skies and environment with both satellites and radio noise.

Somebody or something has to draw the line somewhere, and the Moon would be a good place to make a stand.

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