A rise in the number of satellites in orbit and related space debris is blowing out the costs of astronomy projects as well as impairing humanity's ability to discover stars and potential asteroids, a study has revealed.
Satellites have become smaller and cheaper, allowing companies like Starlink to send up constellations to provide better internet connectivity, and leading to an explosion of the number of devices in orbit, according to a paper published in the Nature Astronomy journal.
The piece, led by John Barentine, was written by an international team of astronomers, including University of Southern Queensland PhD student Jessica Heim, who said the sky was getting "less dark".
"People are probably more familiar with the idea of satellites you can see, when you have an astronomical image, and if a satellite goes through where the image is, it'll look like a streak," Ms Heim said.
"What we were looking at more in the paper is diffused night sky brightness.
"So that's basically where the sum total of all the satellites, all the debris, all the stuff in orbit … that all adds up and contributes to this increased brightness of the night sky.
"Basically, it just makes it less dark, as all the little pieces of stuff will reflect sunlight, and then that gets reflected down and it just has the net effect of making the sky a little bit less dark."
The study investigated the impact that a brighter sky would have on the Vera Rubin Observatory, which is being built in Chile.
It found the brighter night sky would reduce the efficiency of the observatory's Legacy Survey of Space and Time by 7.5 per cent and would add $21.8 million to the project's cost.
The aim of the survey is to capture images of billions of objects, record the time evolution of those sources and, in effect, create the first motion picture of the universe.
"It has a very large field of view doing very long exposures," Ms Heim said.
"More stuff will go through it, [in terms of] streaks.
"It's going to be in an area that is very dark and looking specifically for very dim, faint objects, so it's at a particular weakness [to diffused night sky brightness]."
'Plastic bags' for the cosmos
Ms Heim said other areas of astronomy were impacted by light pollution caused by satellite streaks and diffused night sky brightness.
"Say you're trying to look for near-Earth objects, or looking for possible incoming asteroids — a lot of those surveys are done during the twilight hours … when you can see a lot of these satellites that are in orbit," she said.
"You might miss some of these asteroids that you otherwise could have detected, or you might not know if they're an asteroid or if they're a satellite.
"Anything that has a longer exposure time or a wider field of view is particularly vulnerable."
Marnie Ogg from the Australian Dark Sky Alliance said the findings of the study were not surprising.
"In many ways, astronomers have known about light pollution for hundreds of years, but this is a new domain really," Ms Ogg said.
"It's such a big thing — all of a sudden what we're doing is basically putting the equivalent of tens of thousands plastic bags in rivers, but we're putting them in the night sky."
She said the effects of space junk were more wideranging than just the impact on research.
"There are studies on bird migration patterns that are saying that even birds are being a little bit confused by the fact that there is suddenly a field of stars in the sky that that weren't there before," Ms Ogg said.
Ms Heim said a brighter night sky could affect many species.
"From an ecological perspective, we do know that a lot of species use the stars and Milky Way as part of their navigation," she said.
"So there is the unanswered question of, well, if we have a whole bunch of really bright satellites in orbit, will that confuse them?
"I mean, we don't exactly know at this point.
"The circadian rhythm of wildlife is also determined not by the point sources of light, but how dark overall it is at night versus the daytime.
"If the sky becomes less dark over a longer term, could that impact them in some way? We don't know definitely at this point."
'Another form of colonisation'
The night sky and stars have been central to Indigenous stories around the world for tens of thousands of years.
"There are a lot of cultural traditions where different stars and constellations, the Milky Way, and some of the dimmer stars, too, are important aspects of the teachings of the culture," Ms Heim said.
"Some people have said that this is just another form of colonisation and now it's the sky.
"That's definitely a really important issue that needs increased discussion and awareness."
Ms Ogg said the Dark Sky Alliance was working to educate the public about the benefits of dark skies.
"I'm delighted that the public are really embracing it, and in some ways these launches of these satellite constellations are actually a tool for us to talk about it," she said.
"Because suddenly people are looking up at night and seeing this stream of bright lights travelling fast through the night sky.
"We are getting an increased number of people seeing it saying, 'What is this in the night sky?'"
She said Australians were starting to realise how valuable an asset a dark night was.
"[The alliance] has only been around for about four years," she said.
"We've seen an uptake of not just the general public, but also councils starting to put in light management plans within their region.
"We seem to have looked at conservation as a daytime activity only — but there's a lot of natural cycles going on at night that need to happen without pollutants as well.
"I'm excited to see that people are starting to realise that."
A spokesperson for the Australian Space Agency said the organisation was aware of the emerging issues related to the number of satellites in space.
"Australia is contributing to international discussions on the issue of dark and quiet skies, including through the United Nations Committee on the Peaceful Uses of Outer Space," the spokesperson said.
"The Australian Space Agency also supports discussions that bring stakeholders together to develop practical solutions that seek to address unintended impacts of satellites and satellite constellations on astronomy."
