Nearly three out of every four images obtained by NASA’s new SPHEREx space telescope revealed something many astronomers were afraid of: contamination by artificial objects humans are launching into space.
The findings were reported in a new preprint paper by researchers at NASA’s Ames Research Center, who say that 73.3% of all the images the telescope captured over four months last summer revealed evidence of at least one trail left by SpaceX satellites or other orbital spacecraft.
What may be worst of all is that astronomers aren’t surprised.
With its mission to map the night sky in near-infrared light, NSA’s Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer (SPHEREx) relies on long-exposure imagery that enables it to map large regions of the sky with every viewing.
Unfortunately, long-exposure photography is also ideal for capturing the movement of satellites, an increasing number of which have been placed in orbit in recent years.
Equally troubling is the fact that SPHEREx, from its own position in Earth orbit, had been positioned at an altitude where it was hoped that the number of satellite streaks could be limited. Yet despite such efforts, the new paper featured at the arXiv preprint server reports that, on average, at least two satellite trails were detected in every exposure.
Satellites Mistaken for Cosmic Rays
Astronomers have been raising concerns about this problem already for some time, and presently, there doesn’t appear to be any near-term solution.
Even beyond image contamination, the preprint study also found that several satellites that enter SPHEREx’s field of view are bright enough that they are also triggering the space telescope’s automated system that protects its delicate components from stray cosmic rays.
Designed to shut down the telescope’s data collection when it detects what it suspects are cosmic rays, the new research reveals that some satellites reflect enough light to engage algorithms that control this defense system.
Even in instances where imagery is successfully obtained, albeit with contamination from satellites, the brightness of these orbital objects can effectively obscure objects behind the portions of the telescope’s images where the satellites appeared.
A Growing Concern
The new SphereX findings are only the latest indication that astronomers were right to be concerned about potential light pollution from satellites. In a past study by Sando Kruk and colleagues, Hubble Telescope images had shown an increase in the number of satellites crossing its field of view, rising from contamination shown in just 2.8% of its images, to 5.9% over a period of two decades.
Ideas about how to prevent the issue have focused on using anti-reflective coatings on satellites and other means of reducing their brightness once they reach orbit. However, many modern satellites are large enough that having darker exteriors doesn’t help to significantly mitigate the amount of light they can reflect.
Additionally, the study’s authors note that “Optical reflections are just a fraction of the problem, since satellites also emit and reflect [infrared],” meaning that optical darkening efforts “might even increase their temperature, making them brighter in the IR.”
Worse Before It Gets Better
According to the study’s authors, the problem is likely to worsen before astronomers see any improvements.
“Remarkably, some private operators have announced the intent of deploying 4000 purposely high reflective satellites,” the researchers write, which aim to provide “sunlight on demand.” Such artificial orbital systems, if successfully deployed, would reflect light as much as five times the brightness of the full Moon onto areas of the Earth roughly five kilometers in diameter.
This, the team argues, would potentially have “a catastrophic impact to the quality of the dark sky and the Earth’s inhabitants.”
Fundamentally, the authors hope that bringing additional attention to such issues with their recent study may help to mitigate future concerns about our ever-brightening night sky.
“The widespread contamination addressed in this paper affects multiple areas of astronomical research,” the team says, which they say includes “the study of transient phenomena, deep imaging surveys, spectroscopic studies, and the search for Near-Earth Objects (NEOs), thereby hindering our ability to understand the Universe and protect the Earth.”
The new paper by Alejandro S. Borlaff and colleagues, “SPHEREx confirms predictions for artificial satellite trail pollution in Low Earth Orbit,” appeared at the preprint arXiv server.
Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. A longtime reporter on science, defense, and technology with a focus on space and astronomy, he can be reached at micah@thedebrief.org. Follow him on X @MicahHanks, and at micahhanks.com.