FEATURES
Hubble Asteroid Hunter project
measurements will allow us to study the size distribution of the smallest objects in the solar system and give us important information to study the evolution of the asteroid population and to constrain formation models of the solar system . This result highlights the capability of Hubble to image faint , previously unknown asteroids and represents a new approach to finding asteroids in astronomical archives spanning decades , which may be effectively applied to other datasets . The James Webb Space Telescope , for example , has already detected an extremely small Main Belt Asteroid , between 100 and 200 meters in length ( Müller et al . 2023 ), and this only in its first year of observations . The James Webb Space Telescope archives will likely contain many asteroid interlopers in the images , as the archive builds up over time .
Unexpected discoveries – new strong gravitational lenses
The project ’ s second finding proved to be even more intriguing . Having human eyes on the data can lead to surprising new discoveries . While searching for asteroids , citizen scientists have stumbled across strong gravitational lensing , which they had initially classified as asteroid trails - they appear as curved trails for untrained eyes , after all . Strong gravitational lenses are one of the favourite targets of Hubble ; the telescope observed many such objects discovered from
▼ FIG . 3 : Examples of new strong gravitational lenses found by citizen scientists in the Hubble Space Telescope archives , lying in the background of some famous Hubble observations . the ground over time . To ‘ clean ’ the asteroid trail classifications , we provided detailed instructions to the volunteers to recognize strong gravitational lenses in the images and asked them to tag the images in the forum of the project , Talk ( Hubble Asteroid Hunter » Talk — Zooniverse ). Emily Garvin and a keen citizen scientist , passionate about strong lenses , Claude Cornen inspected the tagged images . They found 252 genuine strong lenses which were not the target of the Hubble observations but lying in the background of some other famous astronomical targets . Checking the existing publications on these objects in ESASky ( https :// sky . esa . int ), we found that 198 of them were new strong lenses ( Garvin et al . 2022 ), not previously reported by other studies or catalogues . This project eventually led to an unbiased search for strong lenses in archival Hubble observations . Because the volunteers were inspecting large field of view Hubble images and not postage stamps of elliptical galaxies , as commonly done in other lens searches , we also found some exotic lens configurations : spiral and edge-on disc galaxies as lenses ; sources lensed by galaxy bulges ; and possible double source plane lenses , as shown in Figure 3 . The high resolution of the Hubble observations reveals tiny arcs and Einstein rings , which are not accessible from the ground . This discovery was only possible because the volunteers made a mistake and tagged objects they were not supposed to .
Satellite trails in the Hubble images
A third result of the project did not come from the extragalactic objects commonly imaged by Hubble , and was not about asteroids , but objects much closer to us – artificial satellites . Hubble ’ s orbit has been gradually decaying , now being at an altitude of 538 km above the Earth . This is below the orbit of many human-made satellites , which can cross the field of view of the observatory during its long exposures . It turns out the combination of crowdsourcing and AI is useful in detecting satellite trails in the images , too . In the www . asteroidhunter . org project , volunteers identified satellites crossing the images on Talk . Compared to the detected asteroids , whose trails appear curved , the satellite trails appear as straight lines across the images . We found that , on average , 2.7 % of Hubble images have been crossed by satellites in the last two decades of observations . The fraction increased over this time , reaching 5 % for ACS in 2021 , the cutoff date of our analysis , as the number of satellites in orbit above Hubble increased , in agreement with other studies ( Stark et al . 2022 ). In Kruk et al . 2023 , we explored the statistics of satellite trails in the images as a function of time , filter and pointing , as well as provided a prediction about the future , as the number of satellites in the so-called ‘ mega-constellations ’ continues to grow .
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