Astronomers have analyzed archival images from NSF’s Zwicky Transient Facility (ZTF), which provides an ideal setup to study the effects of low-Earth-orbit satellite megaconstellations such as SpaceX’s Starlink, and found that the number of affected ZTF images is increasing with time as SpaceX deploys more satellites. Their results appear in the Astrophysical Journal Letters.
The streak from a Starlink satellite appears in this image of the Andromeda galaxy, taken by the Zwicky Transient Facility during twilight on May 19, 2021. Image credit: ZTF / Caltech.
Since 2019, SpaceX has been launching an increasing number of internet satellites into orbit around Earth.
The Starlink constellation now includes nearly 1,800 members orbiting at altitudes of about 550 km.
Astronomers have expressed concerns that that these objects, which can appear as streaks in telescope images, could hamper their scientific observations.
To quantify these effects, University of Warsaw astronomer Przemek Mróz and colleagues studied archival images captured by the Zwicky Transient Facility, an instrument that operates from Caltech’s Palomar Observatory near San Diego.
ZTF scans the entire night sky every two days, cataloguing cosmic objects that explode, blink, or otherwise change over time. This includes everything from supernovae to near-Earth asteroids.
“We decided to specifically study the effects of Starlink satellites because they currently represent the largest low-Earth orbit, or LEO, constellation, and they have well-characterized orbits,” the astronomers said.
The findings shows 5,301 satellite streaks appear in archival ZTF images taken between November 2019 and September 2021.
The streaks are most apparent in so-called twilight observations, those taken at dawn or dusk, which are important for finding near-Earth asteroids that appear close to the sun in the sky.
“In 2019, 0.5% of twilight images were affected, and now almost 20% are affected,” Dr. Mróz said.
In the future, the researchers expect that nearly all of the ZTF images taken during twilight will contain at least one streak, especially after the Starlink constellation reaches 10,000 satellites, a goal SpaceX hopes to reach by 2027.
“We don’t expect Starlink satellites to affect non-twilight images, but if the satellite constellation of other companies goes into higher orbits, this could cause problems for non-twilight observations,” Dr. Mróz said.
The authors also looked at the effectiveness of visors on the Starlink satellites, which SpaceX added beginning in 2020 to block sunlight from reaching the spacecraft.
According to the new observations, the visors reduce the satellite brightness by a factor of 4.6. That dims the satellites down to an apparent brightness level of 6.8 magnitude.
This is still not dim enough to meet standards outlined by the Satellite Constellations 1 (SATCON1) workshop in 2020.
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Przemek Mróz et al. 2022. Impact of the SpaceX Starlink Satellites on the Zwicky Transient Facility Survey Observations. ApJL 924, L30; doi: 10.3847/2041-8213/ac470a
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