Large and publicly available astronomical archives open up new possibilities to search for and study small solar system objects such as asteroids and comets.
A citizen scientist spotted the main-belt asteroid 2001 SE101 passing in front of the Crab Nebula. Image credit: NASA / ESA / Hubble / M. Thévenot, @AstroMelina.
In its 32 years of observations, the NASA/ESA Hubble Space Telescope has produced a rich archive of hundreds of thousands of targeted observations of nebulae, galaxies, clusters of galaxies, and gravitational lenses.
Occasionally, closer objects such as asteroids cross the telescope’s field of view while the targets are being observed, leaving trails in the images.
In 2019, on International Asteroid Day, professional astronomers launched the Hubble Asteroid Hunter citizen science project on the Zooniverse platform, with the goals of visually identifying asteroids in archival images from the European Space Agency Hubble Space Telescope (eHST) archive and studying their properties.
The initiative was developed by the European Science and Technology Centre (ESTEC) and the European Space Astronomy Centre’s Science Data Centre (ESDC), in collaboration with Zooniverse and Google.
First, the astronomers identified more than 37,000 composite images taken between April 2002 and March 2021 with Hubble’s Advanced Camera for Surveys (ACS) and Wide Field Camera 3 (WFC3) instruments.
With a typical observation time of 30 mins, asteroid trails appear as curved lines or streaks in these images.
Over 11,400 members of the public then classified and analyzed these images.
More than 1,000 trails were identified, providing a training set for an automated algorithm based on artificial intelligence.
The combination of citizen science and AI resulted in a final dataset containing 1,701 trails in 1,316 Hubble images.
The project participants also tagged various other astronomical objects, such as gravitational lenses, galaxies and nebulae.
Roughly one third of the asteroid trails seen could be identified and attributed to known asteroids in the International Astronomical Union’s Minor Planet Centre.
This left 1,031 unidentified trails that are faint and likely to be smaller asteroids than those detected in ground-based surveys.
The vast majority of these asteroids are expected to be located in the main asteroid belt between Mars and Jupiter, where asteroids of such small size are as yet poorly studied.
These trails could give the astronomers insightful clues about the conditions in the early Solar System when the planets were forming.
“Citizen science and machine learning are very useful techniques for the systematic search for Solar System objects in existing astronomy science data archives,” the researchers said.
“Our work describes a method for finding new asteroids in astronomical archives that span decades.”
“It could be effectively applied to other datasets, increasing the overall sample of well-characterised small bodies in the Solar System and refining their ephemerides.”
The results were published in a paper in the journal Astronomy & Astrophysics.
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Sandor Kruk et al. 2022. Hubble Asteroid Hunter I. Identifying asteroid trails in Hubble Space Telescope images. A&A 661, A85; doi: 10.1051/0004-6361/202142998
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