In May 2021, I stood in my garden outside Cambridge, U.K., and watched a train of bright specks race across the night sky. These specks were Starlink satellites, 60 of them in total, freshly launched and speeding their way to join the other 1,500 which currently orbit the Earth. These satellites promise to provide cheap, reliable internet to anyone in the world. They also promise to make life very, very difficult for astronomers.
This “mega-constellation” of Starlink satellites is the brainchild of Elon Musk’s company SpaceX. Their plan is something straight out of science fiction: put 42,000 satellites into orbit, and broadcast wireless internet to anyone and everyone, all of the time. Early reviews have been... less than stellar (“unreliable, inconsistent, and foiled by even the merest suggestion of trees”, said The Verge). But the tech will no doubt improve. Like it or not, ubiquitous Starlink internet is coming.
There’s also no reason to think that SpaceX is the only player in town. A number of other companies and countries are all planning their own satellite mega-constellations, from Amazon (3,236 satellites as part of Project Kuiper), OneWeb, and Boeing, to China’s ambitious plan for a 13,000-strong swarm.
Astronomers like myself have been less than enthusiastic about the prospect of a night sky full of artificial satellites. Our most sensitive telescopes are designed to pick up the unimaginably faint signals from planets orbiting distant stars, and galaxies billions of years in the past. How did the first galaxies form after the Big Bang? How fast is the universe expanding? Are there any dangerous asteroids that might crash into Earth? Having tens of thousands of satellites criss-crossing the sky and obscuring the view is going to make answering these questions more difficult.
This is going to be a serious problem for some future projects. The Vera C. Rubin Observatory is an upcoming telescope, located under Chile’s dark skies, that will have the unprecedented ability to photograph the entire sky every few nights. It promises to make massive strides in our understanding of dark energy and dark matter, the structure of our galaxy, and the hunt for our solar system’s elusive Planet Nine.
It will also be severely impacted by satellite constellations. The telescope is sensitive enough to observe some of the faintest visible signals imaginable, with an extremely wide view of the sky. But that also means that satellite trails that cross its view show up as awful wide streaks that ruin the image. Up to a third of all the data taken by the telescope could be seriously affected, hampering its ability to study everything from near-Earth asteroids to the distant universe.
SpaceX has made some effort to dim their satellites—but even the new black-painted versions, called DarkSat, are still pretty bright (they “do not achieve the brightness goals recommended,” according to the International Astronomical Union). And even if SpaceX plays nice with astronomers, the orbital gold-rush is only just getting started. We could have more than 100,000 satellites in orbit around Earth within the next 10 years.
While these satellite swarms are going to make life difficult for astronomers observing the universe in visible light, they are set to be even more problematic for astronomers who work with radio waves—one of the most important tools in an astronomer’s cosmic toolbox. They are emitted by all kinds of things in space, from organic molecules to dying stars. Jodie Foster in the film Contact (playing Ellie Arroway) was listening to the universe using radio waves, and to this day telescopes involved in SETI, the search for extraterrestrial life, use these waves to scan the sky for signs of cosmic intelligence.
All of this work is in jeopardy. Satellite swarms have to communicate with humans on Earth, and they do so using radio waves. It won’t take long before the effect of all these satellites becomes overwhelming: In 10 years time we could have 100,000 radio beacons in the sky, blasting our planet with a wall of radio noise capable of deafening even the most sensitive radio telescope.
The best radio telescope in the world is currently under construction. Dubbed the Square Kilometre Array (SKA)—it’s comprised of individual radio dishes that take up a square kilometer of area—it will be able to scan the sky 20,000 times faster than any existing instrument. It’s so sensitive that it would be able to detect an airport radar on a planet tens of light-years away. But even the SKA will be no match for a sky full of satellites drowning out the faint signals from the universe.
Starlink satellites transmit at a frequency range right in the middle of SKA’s Band 5b—a part of the radio spectrum which astronomers use to hunt for complex organic molecules in space, hoping to understand the origin of life. The more satellites flying around Earth, the harder it will be to use this band for astronomy. Once there are 100,000 satellites up there, it will be a lost cause.
So what can astronomers do? Avoiding the satellite swarms might just be possible. But we’ll have to think outside the box—one might even say outside of Earth.
The far side of the moon might just be the quietest place in the solar system. With over 2,000 miles of solid rock between you and the chatter from planet Earth, it would be the perfect place to get some peace and quiet. It might also be the perfect place for a radio telescope.
Or possibly radio telescopes—plural. NASA has plans for several different lunar instruments, including FarSide and FarView (networks of linked radio antennas spread across the moon’s far side), plus the amazingly ambitious “Lunar Crater Radio Telescope” (which is exactly what it sounds like: a radio telescope built into a crater on the moon). These instruments would be able to study the universe without worrying about radio interference from our very loud and chatty planet.
It must be said that scientists were dreaming of lunar telescopes long before SpaceX began filling the skies with satellites. If Starlink disappeared tomorrow, there would still be a good reason to build a radio telescope on the moon. The longest wavelength radio waves (which astronomers use to study the universe’s first stars) are completely blocked by our ionosphere, and are disrupted by even the tiniest bit of radio interference. So we already had plans to build a telescope on the moon. The coming age of satellite mega-constellations just gives us a reason to hurry up.
These plans aren’t just idle speculation. In 2022 NASA will deliver a range of science experiments to the surface of the moon. Among these will be a machine to examine the radio wave environment, which will gather data critical to the design of future telescopes. Another experiment will land in 2024.
And the U.S. isn’t the only interested country. In 2019, China’s Chang’e-4 lander arrived on the far side of the moon armed with a low-frequency radio wave detector. It was testing the waters for yet another future telescope.
A telescope on the moon won’t come cheap, of course. Building a large observatory on Earth costs hundreds of millions of dollars (at least!) and putting one on the Moon will multiply that into the tens of billions. The high cost, combined with the fact that astronomers are busy developing techniques to mitigate the effect of satellites on our images, means that lunar telescopes are not a “one size fits all” scientific magic bullet. After all, the invention of space telescopes didn’t stop us building telescopes on the ground.
Things will be no different in the future. Telescopes on the moon will open another brand-new window to the universe, and will certainly reveal strange and wonderful things (including, we hope, the first stars which ended the cosmic ‘dark ages’ after the Big Bang). Lunar telescopes will be another tool in our scientific toolkit, though certainly not the only tool we need.
The days of staring up into a clear night sky awash with stars might soon be over. Light pollution has already made stargazing all but impossible in big cities. With the coming age of endless satellite swarms, even our remotest dark skies are threatened. This is a tragedy: The sight of our universe, in all its splendor, is nothing less than a shared human birthright. But there are other worlds, and other skies. And the clearest, most pristine sky of all is waiting for us on the silent surface of the moon. We just need to take that one small step.