As the armada of satellites circling Earth grows, a new study shows astronomical images are marred by streaks of reflected sunlight left behind by fast-moving objects.
For the study, published Jan. 14 in Astrophysical Journal Letters, researchers looked at the effects of Starlink satellites in about 300,000 images taken by an instrument at the Palomar Observatory in Southern California. Between November 2019 and September 2021, they saw a 35-fold increase in the number of corrupted images.
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The streaks may not be enough to compromise the scientific value of the images, the study authors said. But they could complicate efforts to detect potentially dangerous asteroids, said Eric Bellm, a University of Washington astronomer who was not involved in the research.
“There’s definitely some sort of planetary defense aspect here,” he said.
Satellites “have the potential to interfere with ground-based observations by increasing the complexity of differentiating man-made satellites from natural objects like asteroids and comets,” a National Aeronautics and Space Administration spokesperson said. NASA searches for near-Earth objects such as asteroids by looking for bright spots in the night sky that move relative to the stars.
Although mostly invisible to the naked eye, satellites can also hamper observations by amateur and professional astronomers, said astronomer Connie Walker, who was not involved in the new study. She is co-leading an effort by the International Astronomical Union, a non-governmental organization, to mitigate the impacts of so-called satellite constellations on astronomical observations.
Astronomers have been discussing the potential impacts of satellite constellations — groups of similar satellites working together in orbit — for years, said Stanford University astrophysicist Bruce Macintosh, who was not involved in the new research. But the talks have mostly focused on computer models or a limited number of corrupted images, he said.
“This paper helps anchor the models on real data and provides statistics rather than point-in-time images,” he said.
The study focused on the Starlink satellites because they are now the largest constellation of satellites in low orbit, said Przemek Mróz, an astronomer from the University of Warsaw and lead author of the study. Other companies, including Amazon.com Inc.
and London-based OneWeb are developing satellite constellations.
Amazon has taken steps to reduce the impacts of its satellites on astronomical observations and is working with astronomers to better understand their concerns, a company spokesperson said.
A OneWeb spokeswoman said the company is committed to reducing the effects of its satellites on sightings. “We publicly provide data on where our satellites are at any given time, helping astronomers adjust their observations and avoid disruption,” she said.
Space Exploration Technologies Corp., the official name of SpaceX, did not respond to requests for comment. “We strongly believe in the importance of a natural night sky that we can all enjoy,” the company said in 2020, adding that it was working to understand how to limit potential issues caused by its Starlink satellites.
Potential problems with satellite constellations could worsen as more satellites are deployed, astronomers say. “Astronomy faces a tipping point situation of increasing interference with observations and loss of science,” Dr Walker said.
The Federal Communications Commission has licensed 12,000 Starlink satellites as part of a plan to extend high-speed Internet service to the entire planet, including remote areas. Commission filings indicate SpaceX wants to increase the number to at least 42,000. About 1,740 Starlink satellites are active or moving to operational orbits, SpaceX chief executive Elon Musk said.
OneWeb has launched 394 satellites from its planned constellation of 648 satellites. Amazon aims to put more than 3,000 satellites into orbit by 2029 as part of Project Kuiper, a plan to provide high-speed internet access around the world. Last year, China announced plans to launch a network of 13,000 telecommunications satellites.
The impact of satellites on images depends in part on how long astronomers use an instrument to observe a celestial object.
The streaks seen in images captured by the Palomar instrument, which typically makes 30-second observations, do not mean the image is ruined, said Tom Prince, a California Institute of Technology physicist and co-author of the news. study. But, he added, “this may not be true for other observatories.”
Astronomers using the WM Keck Observatory in Hawaii often stare at faint celestial objects for long periods of time, sometimes for hours. If a satellite goes through prolonged exposure, the “data could be irrevocably damaged,” said John O’Meara, the observatory’s chief scientist.
The software can help remove satellite footage, Dr. Bellm said, but can still corrupt image data.
Satellites also pose a challenge for radio astronomy, in which images are created with radio waves rather than light.
Signals that telecommunications satellites send to Earth have sometimes drowned out radio signals from celestial objects, said Philip Diamond, chief executive of the Square Kilometer Array, a radio telescope project that began construction last year. “Signals from satellites can be millions of times stronger than the brightest radio sources in the sky,” he said.
Dr Prince said SpaceX had “acted responsibly” in taking steps to mitigate potential issues caused by Starlink. The company began launching satellites fitted with visors that shield their more reflective parts in mid-2020. The new study showed that Starlink satellites with visors lost their brightness by a factor of about five.
Amazon plans to launch a prototype satellite equipped with a sunshield by the end of the year.
Dr Macintosh called for more international regulations and agreements to limit the impact of satellites on astronomy.
SpaceX and other companies that provide satellite internet in the United States must obtain a license from the FCC. The agency’s rules cover possible interference with radio astronomy but do not extend to light reflected from satellites, an FCC spokesperson said.
Dr Macintosh said he believed that “with caution, co-operation and some regulation” the potential problems posed by satellite constellations could be overcome even if more satellites came up.
“The genie doesn’t go back into the bottle,” he said.
Write to Aylin Woodward at [email protected]
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