Elon Musk will soon offer broadband connectivity to the entire world, delivered through a mega-constellation of 12,000 satellites. Named Starlink and launched by Musk’s privately owned company SpaceX, the system will benefit remote communities and developing countries. But it will also be enormously detrimental to astronomy, which depends on dark and radio-quiet skies.
The night sky has always been a source of wonder and enlightenment. It has enabled humanity to keep time, find our way across oceans and deserts and test the laws of physics. Astronomers are constantly discovering new worlds, investigating the cosmology of the universe and measuring gravitational waves within space-time itself.
If you look up on a clear night, you will likely see a tiny point of light moving quickly across the sky. Seeing satellites is a regular occurrence. However, you still see more stars than satellites, since more than 9,000 stars can be seen with the naked eye.
Unfortunately, light pollution from cities is already affecting people’s experience of the night sky. Many people have never seen the Milky Way, the band of stars, gas and dust that extends across the night sky. What will happen when satellites dominate the sky?
Within the next decade, the number of satellites in Earth’s orbit could increase tenfold, from about 5,000 to 50,000, as mega-constellations are launched by SpaceX and other companies like Amazon, OneWeb and Telesat, which are just getting started. SpaceX already has plans to expand Starlink to 42,000 satellites, resulting in approximately one satellite within every single square-degree of sky. Although these satellites would provide communications benefits, they would also be a form of pollution.
Satellites are already interfering with radio astronomy, which studies solar activity, black holes, pulsars, star formation and the echoes of the Big Bang. A tenfold increase in communications satellites would exacerbate this interference and probably require an expansion in the range of frequencies used by the satellites, rendering more regions of the electromagnetic spectrum unavailable to radio telescopes.
At present, satellites are only an occasional nuisance for optical and near-infrared astronomy, leaving bright streaks across some images taken through telescopes. But a tenfold increase in satellites could be very disruptive to these observations, even if the satellites are not visible to the naked eye.
Scientists will seek to reduce these disruptions by developing new methods of data analysis. But images will inevitably be distorted and valuable data lost. One particular concern is the effect that so many satellites could have on the early detection of asteroids’ Earth impact trajectories. The consequences of a delay in the detection of such an object could be cataclysmic, for instance, if it prevented the launch of a redirection mission.
SpaceX has already launched its first 120 satellites, and long-duration images taken through a telescope in Chile have been marred by streaks of light from its satellites. The International Astronomical Union, which represents 13,000 astronomers worldwide, responded with a statement defending "a dark and radio-quiet sky as not only essential to advancing our understanding of the universe of which we are a part, but also as a resource for all humanity."
Musk has responded to such concerns with defensiveness, tweeting: "There are already 4900 satellites in orbit, which people notice ~0% of the time. Starlink won’t be seen by anyone unless looking very carefully and will have ~0% impact on advancements in astronomy."
Stopping mega-constellations is not an option. There are no international or domestic laws that prevent companies from placing thousands of satellites in orbit, even if doing so causes major problems.
There is, however, hope for mitigating the damage - by having the polluters pay. SpaceX and other companies that are ruining the night sky could support astronomy by helping to place telescopes into orbit, or even on the moon.
Humanity needs telescopes. Astronomy is essential to understanding the universe and where we come from. It is also essential to the long-term development of space, the moon and Mars. Musk understands all this and has tweeted that we need to move telescopes into orbit.
Musk is well positioned to reduce the severity of the problem that he is helping to create. He could take the lead in launching telescopes as a new form of philanthropy, saving astronomy from satellites.
Michael Byers and Aaron Boley teach international relations and astronomy, respectively, at the University of British Columbia. They co-direct the Outer Space Institute, and wrote this piece for the Los Angeles Times.