Megaconstellations of satellites are burning up in our atmosphere. That could have consequences

If, on a clear night, you were to gaze up into the blackness of the sky, you would expect to see nothing but the magnificent Milky Way stretching out above you, billions of stars twinkling in place.

Instead, every few minutes or so, you will most likely also see an ersatz star breaking through an otherwise static sky, silently moving across the stars.

These are satellites, and there are thousands of them in orbit. When they've outlived their usefulness, most of them will come tumbling back down through Earth's atmosphere, burning up. 

Scientists are now looking at how this process is dumping potentially harmful particles in our atmosphere. And though the exact consequences are still unknown, some are calling it a wake-up call.

There are an estimated 11,500 tonnes of space objects orbiting Earth, which would include even the smallest pieces around one millimetre in size (likely satellite collisions). But there are far larger objects in space, including spent rocket stages and upwards of 9,000 functioning satellites. More than half of them are SpaceX Starlinks, which provide internet services.

As of publication, there are roughly 5,200 Starlink satellites, but SpaceX has plans to put up upwards of 42,000.

And it's not the only company planning to launch these "megaconstellations" of satellites. Companies like OneWeb and Amazon and countries like China all have plans to put thousands more satellites in orbit.

What goes up eventually has to come down. In the case of Starlink, these satellites have a lifespan of roughly five years, after which they're deorbited. They then burn up in our atmosphere. 

A new study, published last week in the journal Geophysical Research Letters, suggests that the particles left behind could potentially affect our ozone layer.

And in a study published in October in the Proceedings of the National Academy of Scientists, several scientists from the U.S. National Oceanic and Atmospheric Administration (NOAA) examined particles in the stratosphere.

The researchers were surprised to find a variety of vapourized metals in the stratosphere that they linked to satellites and spent rocket boosters.

"It actually wasn't something we were looking for," said Daniel Murphy, a chemical sciences laboratory research chemist at NOAA, who led the study.

"In looking at the data, I started seeing not just the metals you expect from meteors, which are things like iron and magnesium, but also weird metals."

The first of those was lithium, which left Murphy scratching his head, since there's almost no lithium in meteors that burn up in the atmosphere. But then more and more started popping out — in all, 20 different metals — including an excess of aluminum, as well as niobium and hafnium.