The true impact of SpaceX’s Starlink constellation on astronomy is coming into focus

Since SpaceX launched its first batch of satellites with internet rays last year, astronomers have watched with fear as the company shot more and more spacecraft into space. Could this balloon-filling constellation of bright satellites fill the night sky with artificial light and obscure the observations of the universe for years? Now, new data partially confirms what many astronomers feared since that initial launch.

Until now, people have been somewhat in the dark about the true impact of SpaceX’s internet-from-space project called Starlink, which represents nearly 12,000 of these satellites in orbit. SpaceX’s satellites are super-bright compared to others, and astronomers worried that with so many luminous satellites in the sky, the chances of one going past a telescope and obscuring an image will increase.

It turns out that some astronomers have cause for concern. Certain types of astronomy can be affected more negatively than others, according to a peer-reviewed study, particularly those that search large swaths of sky for long, distant objects. That means that scientists looking for distant objects outside of Neptune – including the hunt for the mysterious Planet Nine – may have problems when Starlink is completed. In addition, Starlink may be much more visible during twilight, or the first few hours of the night, which could be a major problem when hunting massive asteroids headed for Earth. “It depends on what science you do, and that’s what it really comes down to,” Jonathan McDowell, astrophysicist at Harvard and aerospace expert who wrote the study accepted by Astrophysical Journal Letters, says The edge.

Meanwhile, scientists are also learning whether SpaceX’s attempt to reduce the brightness of its satellites will really work. The company coated one of its satellites in an attempt to make it appear less visible in the sky. Now the first observations of that satellite are published and the coating works – but it may not be enough to make everyone happy. “It doesn’t solve the problem,” Jeremy Tregloan-Reed, a researcher at the University of Antofagasta and lead author of the study, which is undergoing peer review on Astronomy and Astrophysics Letters, says The edge. “But it shows that SpaceX has taken over the concerns of astronomers and it seems to resolve the situation.”

How Starlink will influence astronomers

For astronomers, light is everything. Observing celestial objects in different wavelengths of light is the best method we have for exploring the universe. That’s why adding artificial light to the sky drives so many scientists crazy. Some astronomers take long-exposure images of the sky and collect as much light as possible from distant objects – and when a bright satellite reflecting light from the sun rises overhead, it can leave a long white streak ruining the image.

Of course, the sky is a large canvas, and a small satellite will not become a big headache. A large number of factors dictate exactly how and when satellites will be a problem. The size, shape, height and path of a satellite around the Earth all affect exactly how much light it reflects from the sun and where people will see it most. Meanwhile, the time of year and the time of night determine how much sunlight shines on a satellite at any given time.

A batch of 60 SpaceX Starlink satellites before deployment.
Image: SpaceX

To find out the exact impression of Starlink at night, McDowell made an extensive simulation based on what we know about where all Starlink satellites are heading. Prior to the launch of its constellation, SpaceX had to file multiple requests with the Federal Communications Commission, specifying where it wanted to send all of its spacecraft. Using that information, McDowell provided a snapshot of which areas will see the most satellites overhead and which times of the night will be worst for observations.

In the more northerly and southern latitudes, Starlink satellites will dominate the horizon during the first and last few hours of the night. In the summer it will be much worse, with hundreds of satellites visible to people in the countryside, away from light pollution from the city. ‘Where I live [Boston]I see the planes floating above Logan [Airport] on the horizon, ”says McDowell. “It will look like this, but it will be satellites and there will be many.” SpaceX declined to comment on this story.

While people who live in cities and towns don’t really notice it, this means bad news for those who hunt for distant objects with long exposures. “The longer you open the shutter, the more likely you are to have an observation obstructed by one of these bright streaks,” Michele Bannister, a planetary astronomer at the University of Canterbury in New Zealand who helped McDowell with his research The edge. That means those who hunt Planet Nine and objects on the edge of the solar system have some cause for concern.

In addition, asteroid hunters will be additionally affected by this zodiac sign, McDowell says. “They really hosed, because they have to watch the twilight,” he says. Scientists looking for asteroids orbiting near Earth often search for these objects near the Sun; they observe just after sunset when they can see the part of the sky near the sun that is too bright to see during the day. “That’s where the problem with illuminated Starlink satellites is the worst“He says.” Even from regular observers at 30 degrees latitude, they will have serious problems. “

The true impact of SpaceX’s Starlink constellation on astronomy is coming into focus 1

The Starlink satellites were captured when they came above the Cerro Tololo Inter-American Observatory in Chile.
Image: NSF’s National Optical-Infrared Astronomy Research Laboratory / CTIO / AURA / DELVE

As for what that means for these astronomical fields, an obvious concern is that a potentially dangerous asteroid could go unnoticed until it’s too late to act properly. It is also possible that observers will have to take expensive countermeasures to get the desired images. “It may mean that you have to observe twice as long if you have to throw away half of your data,” says McDowell. “So that’s expensive. Or you may have to change the design of your telescope to stop reflections from a satellite.”

At least the silver lining here is that the McDowell study found that Starlink doesn’t really have a big effect on the work of many other astronomers, especially those who only look at small slices of the night sky for certain periods of time. But his work goes against what SpaceX CEO Elon Musk has said about Starlink and its implications for astronomy. “I am convinced that we will not have any impact on astronomical discoveries. Zero, ”Musk said during a space conference in early March. “That is my prediction. And we will take corrective action if it is above zero. “

Despite Musk’s bold statement, the truth is that SpaceX has already taken some remedies, but new research shows it may not be enough to silence all of the company’s critics.

A jacket without colors

At its third Starlink launch in January, SpaceX included a satellite painted with an experimental coating, intended to darken the reflectivity of the spacecraft. Nicknamed DarkSat, the spacecraft was of particular interest to amateur satellite followers. Several observatories have taken photos of DarkSat as it passed overhead to measure how much weaker it appears compared to its cohort.

The answer, it seems, is that DarkSat is indeed darker, but only slightly. Once it reached its last orbit, the satellite appeared 55 percent weaker compared to another bright Starlink satellite, according to the Tregloan-Reed study. That is based on the first observations he made with a telescope at the Ckoirama observatory in Chile. “The DarkSat coating ensures that the satellite can no longer be seen with the naked eye,” says Tregloan-Reed.

That’s a big cut, but 55 percent may not be enough for some observatories. The Vera Rubin observatory in Chile is still under construction, but it has an enormous task to investigate the whole night sky. “It will be able to give us the history of the solar system in absolutely intricate and astonishing details,” said the survey’s Bannister. “And I think that’s definitely under threat.” Observatory people have estimated that the Starlink satellites must be even weaker than DarkSat to really stay out of the way and do not saturate the collected images.

The good news is that SpaceX has hinted that more extreme countermeasures are on the way. During the last launch, a SpaceX employee noted that while the coated satellite showed “a noticeable decrease” in brightness, a future Starlink satellite could be equipped with a sunshade to further reduce reflectivity. “We have a few other ideas that we think could reduce reflectivity even more, the most promising is a parasol that would work the same way as a parasol or a sun visor – but for the satellite,” Jessica Anderson, a Head of production engineer at SpaceX, said during the live stream.

Tregloan-Reed says he has hope for some kind of shade. “If that worked, it would theoretically block sunlight completely,” he says.

Still, that doesn’t solve every astronomical problem, because even an obscured satellite can still be a nuisance. For example, astronomers looking for planets outside our solar system often take very sensitive measurements of distant stars, looking for decreases in their brightness that may indicate an alien planet passing by. If a satellite, even a dark one, passed by for a star that someone was observing, it could interfere with the search for these alien worlds.

Whatever happens, it looks like a giant constellation will have some kind of negative impact someone – it cannot be helped. And looking at the big picture, SpaceX isn’t alone in its attempt to create a mega constellation of satellites. The company simply gets the most attention because it represents the largest number of spacecraft, and the vehicles are large, bright and lower in the sky compared to other proposed constellations. Others like OneWeb and Amazon also want to fill the air with vehicles that blast internet.

Such a large influx of artificial light points is really at the heart of the problem. “I understand the importance of Starlink; I see the benefits of global internet, ”says Tregloan-Reed. “It’s just the huge numbers that worry me.”

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