SpaceX's Starlink constellation, designed to provide global internet access, has revolutionized connectivity. However, its growing presence in low Earth orbit (LEO) has raised concerns among astronomers. These satellites, numbering nearly 1,800 and orbiting at approximately 550 kilometers, can appear as streaks in telescope images, potentially hindering scientific observations.
The Zwicky Transient Facility (ZTF), operating from Caltech's Palomar Observatory, has been instrumental in quantifying these effects. A recent study published in The Astrophysical Journal Letters analyzed archival ZTF images to assess the impact of Starlink satellites on astronomical research.
The ZTF plays a crucial role in scanning the night sky, cataloging transient objects like supernovae and near-Earth asteroids. It captures images of the entire night sky every two days, making it a valuable asset for astronomical discoveries. The ZTF team chose to study Starlink because it is the largest LEO constellation with well-defined orbits.
The study revealed a significant increase in satellite streaks in ZTF images. From November 2019 to September 2021, 5,301 satellite streaks were identified. These streaks are particularly noticeable in twilight observations, which are essential for detecting near-Earth asteroids that appear close to the sun. Twilight images affected by satellite streaks jumped from 0.5% in 2019 to almost 20%.
Przemek Mróz, the study's lead author, anticipates that nearly all twilight images will contain at least one streak once the Starlink constellation reaches its goal of 10,000 satellites by 2027.
Despite the increase in streaks, the study notes that ZTF science operations have not been significantly impacted. Tom Prince, co-author of the study, mentions that a single streak affects less than one-tenth of a percent of the pixels in a ZTF image. While there is a small chance of missing an asteroid or other event hidden behind a streak, the impact is relatively minor compared to weather conditions like cloudy skies.
Software solutions are being developed to mitigate these issues:
SpaceX has implemented visors on its satellites since 2020 to reduce their brightness. ZTF observations indicate that these visors reduce the brightness of the satellites by a factor of five, dimming them to an apparent brightness level of 6.8 magnitude. While this is a step in the right direction, it still falls short of the seventh magnitude or fainter standard recommended by the Satellite Constellations 1 (SATCON1) workshop, which brought together experts to discuss the impact of satellite constellations on astronomy.
The study's findings are specific to ZTF. The upcoming Vera C. Rubin Observatory, with its more sensitive imager, is expected to be more significantly affected by satellite streaks. This highlights the need for continued research and development of mitigation strategies to minimize the impact of satellite constellations on future astronomical observations.
Keywords: Starlink, satellites, astronomy, Zwicky Transient Facility, ZTF, Palomar Observatory, satellite streaks, astronomical observations, Vera C. Rubin Observatory, space exploration.
