The combination of space junk and functional satellite constellations like SpaceX’s Starlink has made astronomers concerned that orbiting material could interfere with observations. And given that researchers are currently debating whether one observation represents one of the most distant supernovae ever observed, or a spent Russian booster, it’s no surprise. That is.
This clutter is clearly a big problem for ground observatories located below everything in orbit. However, some observatories, including the Hubble Space Telescope, are in low-Earth orbit and are therefore placed under many satellites. A new study of Hubble images also shows an increasing number of satellite tracks in the images. So far, this hasn’t seriously compromised the science, but it’s clear that orbiting observatories aren’t immune to these problems.
leave the track
This research comes from the Hubble Asteroid Hunter, a citizen science project. The project organized volunteers to search for asteroid trails left behind by the Hubble Space Telescope’s long-exposure observations. If an asteroid happens to pass through Hubble’s field of view during this exposure, it could leave a short streak in the resulting image. But participants began to notice streaks across Hubble’s entire field of view in one image (the project maintains a forum where volunteers can discuss their work).
Something as far away as an asteroid cannot move fast enough to leave such a long trail. So the only realistic explanation is something closer: satellites.
Informal identification of this satellite was not sufficient to obtain reliable statistics on its number. However, it provided researchers with a dataset sufficient to train an AI system to identify tracks within a much larger image database. (They actually trained two of him and found consistent results.) Once trained, the AI was trained on two of his Hubble cameras (an advanced camera for research and a widefield camera). Released to a complete database of images from cameras 3). One with an exposure long enough for the satellite to completely cross Hubble’s field of view.
Not surprisingly, many satellite crossings were identified. I am concerned about trends. Between 2002 and his 2005, his 2.8% of long exposures taken by Hubble contained satellite trails. From 2018 to 2021, that percentage rose to his 4.3%. There was also a significant increase in wide-field cameras 3 that were inactive throughout the study period. Depending on the camera, the rate of increase during this period was 60-70%.
snuggle up to the constellations
Researchers note that tracks appear more frequently at lower wavelengths. Satellites are less likely to be visible in UV. Satellites also appeared more frequently when Hubble was pointed along the equator. The researchers suggest that this indicates that most orbits are left by satellites in geostationary orbit, which often lie along the equator.
Fortunately, most of the mega-constellations put into orbit are below Hubble’s altitude, so their addition won’t really affect these numbers. It’s slowly collapsing along with it, so it’s possible that it will eventually fall into the region where these constellations reside before the instruments start to malfunction. We also note that similar problems may occur due to the close-Earth orbit of .
Nature Astronomy, 2023. DOI: 10.1038/s41550-023-01903-3 (About DOI).
