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Friday, May 24, 2024

Astronomers Want to Save Dark Skies from Satellite Swarms

Last Thursday, on the same day that SpaceX launched 49 Starlink internet relay satellites—joining more than 2,000 others in what is by far the biggest satellite network—the largest global organization of astronomers launched a new institution to save the night sky from the brightness and radio-frequency interference of satellites.

The new Centre for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference comes from the International Astronomical Union, which includes professional astronomers from more than 90 countries, including those who famously (or infamously) demoted Pluto in 2006. The center will have two cohosts: the National Science Foundation’s NOIRLab—named after optical and infrared astronomy, not noir fiction—in Tucson, Arizona, and the radio-astronomy-focused Square Kilometer Array Observatory in Manchester, England. The center will coordinate research and advocacy related to reducing the effects of light and radio interference on scientific observations.

“In the past, the main source of interference was the light pollution from the ground,” said Piero Benvenuti, emeritus astronomer at the University of Padova, Italy, and the center’s first director, at a virtual press conference last Thursday. Astronomers have long worried about sprawling cities with ubiquitous outdoor lights hindering their view as they attempt to peer into the sky with their scopes, as well as radio stations and communication signals, including mobile phones and wireless networks, messing with their radio observations.

Now astronomers’ concerns have shifted, and they’re looking up. “Optical and infrared trails and radio transmission by satellite constellations pose an existential threat to astronomical observations from the ground,” said Debra Elmegreen, IAU president and an astronomer at Vassar College, at the same event.

In just a few years, after many launches of batches of satellites, SpaceX’s Starlink has become the biggest artificial constellation in the sky. It now provides broadband internet access to more than 100,000 users, with more to come. Within a few years, also counting other satellite mega-constellations like Amazon’s Project Kuiper, China’s Starnet/GW, and Canada’s Telesat, there could be as many as 100,000 satellites in orbit, each giving off a little light and sending down radio signals.

Benvenuti and his colleagues worry about how hard it will be to do space science if satellites end up photobombing astronomers’ images. The establishment of the new IAU center signals that maintaining dark skies and addressing the effects of these constellations have now become international priorities. Over the past two years, many of the astronomers with leadership roles in the new center had already organized online workshops which produced detailed reports, including SATCON 1 and 2 in the US, and the international Dark and Quiet Skies 1 and 2. Each report argues that much more needs to be done to address the effects of thousands of satellites in low Earth orbit; the window of opportunity is “narrow and closing,” as the SATCON 2 report puts it.

The new center includes four groups, or “hubs.” One, called SatHub, will collect data from professional and amateur astronomers, including images of satellite trails, while encouraging companies to share their data, so that astronomers can better minimize satellites’ effects on their work. Another will communicate with industry experts, in the hope that companies will build their new satellites to be less reflective and avoid the radio frequencies that telescopes use. Another hub will focus on making national and international policy recommendations. The final one will coordinate community engagement, collaborating with indigenous communities, environmentalists, astro-tourism groups, the planetarium community, and others with an interest in limiting light pollution and preserving dark, quiet skies for everyone.

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Jessica Heim, head of the community engagement hub and an expert in cultural astronomy at the University of Southern Queensland in Australia, points out that some indigenous members of her previous SATCON working group view the proliferation of satellite constellations as a new form of colonization. “Satellites literally interrupt our relationship with the stars and ceremonial ways of connecting with them, and if light pollution is erasing indigenous stories, these satellites are rewriting them,” she said at the media event on Thursday, quoting indigenous speakers. The night sky holds a cultural importance for many indigenous peoples, and for others too, and it should be considered part of the environment, she said.

The new center has been well supported throughout the astronomical community. “Now with the amount of infrastructure that’s going up, it’s going to be very critical that light mitigation be part of the satellite design, to ensure that we can carry out astronomical research and to preserve the night sky for future generations,” says Aaron Boley, a planetary scientist at the University of British Columbia and cofounder of the Outer Space Institute, which is not affiliated with the center. In recently published research, he and his colleagues estimated that in a few years, once the number of orbiting satellites reaches about 65,000, they’ll make up about one in 10 lights one can see in the night sky, either with telescopes or the naked eye.

Some astronomers have already witnessed the effects of satellite swarms. Last month, a team of astronomers published findings based on their observations using an instrument called the Zwicky Transient Facility at Palomar Observatory near San Diego. They found that 18 percent of their images taken at twilight in 2021 contained satellite streaks, compared to less than 0.5 percent two years earlier, though only a small fraction of pixels were affected. (Satellites are usually most visible in the sky at twilight.)

“Given that we are one of the largest field-of-view instruments and operate a significant fraction of the time in twilight, pointed as close to the sun as we are comfortable, it is not surprising that many ZTF images have a satellite streak,” Przemek Mróz, an astronomer at the University of Warsaw and lead author of the study, wrote in an email to WIRED. He expects that by the end of this decade, nearly all of their telescope images taken at twilight will have these streaks running through them. Mróz anticipates that satellite light will also affect the sensitive imager of the massive National Science Foundation-funded Vera Rubin Observatory in northern Chile. That telescope has been in the works for decades, and its “first light” is planned for next year.

Astronomers are also concerned that this light will make it harder to spot certain kinds of objects in the sky, including near-Earth asteroids and comets, like the planet-killing variety in the movie Don’t Look Up. Surveys for such asteroids are typically done during twilight. “This leads to the possibility of confusion, data loss, and ultimately a loss of warning time,” Boley says. In terms of radio signals—the “quiet skies” part of the new center’s mission—astronomers anticipate interference when satellites downlink data on frequencies near those used by radio telescopes. For example, measurements of intergalactic radio emissions and those from within the Milky Way could be affected.

“In 10 years, if there are no changes, we’ll have a very congested region in low Earth orbit. It results in a constant struggle to understand what’s real, what’s a natural phenomenon, and what’s not,” Boley says.

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