Elon Musk’s Starlink satellites are leaving tracks that affect twilight observations

• The growing number of Starlink satellites is leaving tracks in images captured by the Zwicky Transient Facility (ZTF).
• These tracks could affect twilight observations in finding objects like comets and asteroids.
• The problem could increase with more Starlink satellites in orbit.

Elon Musk’s SpaceX is scheduled to launch the next batch of Starlink satellites later today. The next 49 satellites will join the growing constellation of over 1,800 Starlink satellites in Low Earth Orbit (LOE) to provide broadband internet connectivity especially. SpaceX has an approval to set up a total of 12,000 Starlink satellites which means there’s still a long line of launches lined up.

The worry and threat about space getting crowded is already a concern with growing interest of not just government but private entities funding and launching space programs. But a more major and immediate concern are the tracks left by Starlink satellites in images captured from a survey telescope, according to a report by ArsTechnica.

The Zwicky Transient Facility (ZTF) at the Palomar Observatory, California. This is a time-domain survey, and as explained by the California Institute of Technology, it scans more than 3750 square degrees an hour to a depth of 20.5 mag to help discover young supernovae nightly and it also searches for rare and exotic transients. The telescope used here has repeated imaging of the northern sky and collects almost 300 observations every year.

The ZTF’s camera has a large 47 square degree field of view which often results in having a Starlink satellite in each image. According to data collected between November 2019 and September 2021, the initial period with only around 100 Starlink satellites in orbit there would be none detected for at least 10 days. But once the count reached over 1,500, the ZTF would capture over 200 satellites in the 10-day period.

The effects

This resulted in twilight observations getting affected by the bright appearance of the Starlink satellites. During late 2020, around 6 per cent of the twilight images were affected but by late 2021 it increased to 18 per cent. After complaints from the astronomy community SpaceX put visors in the later batch of Starlink satellites which helped reduce the visibility of these satellites but it did not meet the actual target.

With twilight observations getting affected it could make it difficult to search for objects like comets and asteroids. The satellite tracks however don’t really affect observations since the observatory’s software identifies them. And the chances of missing a rare event because of a Starlink is very slim at 0.04 per cent.

But the count of Starlink satellites in orbit is only going to increase and even though SpaceX has approval for 12,000 of them, the future target is over 40,000 of satellites. The possibility of other companies launching more satellites is also there which increases the likelihood of the issue even more.

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