A study conducted on the observations of the ZTF (Zwicky Transient Facility) observatory shows that one in five snapshots captured at dawn or dusk at the end of 2021 is already affected by the Starlink constellation. Ultimately, and with the presence of other operators, the scientific teams face a major challenge.
They note, however, that the current impact remains limited.
The little strokes, the little strokes, a lot of little strokes
To discover asteroids whose orbit is close to the Earth, observatories such as the ZTF use techniques using very sensitive sensors and wide-angle optics. This allows them to cover a significant portion of the night sky and detect, perhaps, an unknown “point” moving there faster than a star. Like an asteroid. An exercise which, due to orbital mechanics, is more fruitful a few hours before dawn, or just after dusk.
But it is also during these hours that it is easiest to see flares », the reflections of the sun on the panels or on the surface of the satellites in low orbit. The phenomenon is not new, a large part of the amateurs of astronomical observation know the famous reflections of the Iridium satellites in the years 2000. On the images of the telescopes, they result in a luminous line which crosses the image. Except that we have recently entered the era of super and megaconstellations which use or will use between a few hundred and ten thousand satellites.
Inflation according to Starlink
The best-known of the superconstellations, which critics are currently focusing on, is SpaceX’s Starlink. It represents, with more than 2,000 units today, the largest population of satellites in orbit.
It is its impact that a team wanted to measure, which observed the readings of the ZTF observatory over an extended period from November 2019 to September 2021. It noted 5,301 “lines” attributed to Starlink satellites, a number that is increasing sharply, in direct connection with the deployment of the constellation. Indeed, the number of detections (or pollutions) is estimated at 0.5% of shots in November 2019, 18% of these shots in August 2021 and 20% at the end of the year.
Since the scientific article was written, almost 250 additional satellites have already taken off! The conclusions are very simple: if the constellation reaches 10,000 units in orbit, then each shot from a telescope like the ZTF will show at least one “line” of a Starlink satellite.
Scratched cliches, ruined cliches?
The study is not there to throw stones at Elon Musk or his teams, but it aims to clearly study the impact of the constellation. For example, it highlights the efforts made to communicate with scientists or to reduce the number of stray reflections with the installation of coatings and sun visors. This effectively renders Starlink satellites “invisible” in the dead of night (and that’s good news!), but only reduces their signature in snapshots near dawn and dusk.
On the other hand, it is not fair to say that these images are good to throw away because there is a trace of a Starlink satellite passing through it. However, this remains a nuisance, because it is impossible at the instant T to know what is “behind” the trace. On a normal sky, of course, it is possible to reconstruct using software (but it is time-consuming) the image without Starlink. The fact remains that if you are looking for a transient signal which, precisely, passed there, it is missed.
In fact, the scientists explain that the traces have a minor impact for the moment, especially in comparison to other hazards, like, well, clouds. But if it concerns all the images, with sometimes (or all the time) multiple traces, not only will the study of the negatives take longer, but it could be significantly disturbed. And even more for other telescopes with an even wider field than the ZTF, such as the Vera Rubin, under construction in Chile. It’s annoying, especially when these telescopes are used for the detection of asteroids, some of which could be dangerous.
Starlink and… many more
However, it is towards this scenario that the news tends. It will be understood, Starlink is not the only company to deploy its constellation, even if it is the first. For example, there are more than 400 OneWeb satellites in higher orbits, but which disrupt other observations… And many other operators are getting into it: Amazon, of course, but also O3B and several competitors for the gigantic Chinese market.
At the current rate, by the end of the decade, there may be more features than stars… This study comes in addition to others, sometimes more alarmist on the part of astronomers, but also to growing concerns about in-orbit traffic.
Sources:
TechRadar
, IOP Science
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