Citizen Scientists Identify New Sample of Over 1,000 Hidden Asteroids in Hubble’s Archival Data

After more than thirty years in operation, the Hubble Space Telescope continues to make astronomical discoveries which help scientists gain more knowledge about the universe. There are also cases where the venerable telescope makes discoveries by accident.

Capturing Wandering Asteroids

It has been widely accepted that asteroids are materials which were left over from the birth of the Solar System around 4.5 billion years ago. These celestial objects come in various shapes and sizes, ranging from pebble-sized rocks to planetoids.

It has been a challenge for astronomers to observe these space rocks since they are faint and constantly in motion as they orbit the Sun. Fortunately, the rapid geocentric orbit of the Hubble telescope enables it to capture wandering asteroids with the help of distinct curved trails they leave in Hubble exposures. As Hubble orbits our planet, its point of view changes while observing asteroids following their orbits.

Asteroids have also been known to "photobomb" images collected by Hubble of distant celestial objects like the UGC 12158 galaxy. Scientists can determine the distances of asteroids and estimate the shapes of their orbits by knowing Hubble's position when it captured exposures of asteroids and measured the curvature of the streaks they leave. The ability to perform this method with large samples enables astronomers to test theories regarding the formation and evolution of the Main Asteroid Belt.

According to a widely accepted model, small asteroids are actually fragments of larger asteroids which have been colliding and grinding each other down over billions of years. However, a competing theory suggests that small bodies formed as they appear today billions of years ago and have not changed much since.

Still, astronomers cannot provide any plausible explanations as to why these smaller asteroids would fail to accumulate more dust from the circumstellar disk that surrounded our Sun billions of years ago.

Pioneering Approach in Identifying Asteroids

With the help of machine learning algorithms, a group of citizen scientists identified a new collection of hidden asteroids. The method they used represents a new strategy for finding objects in decades-old data which can also be applied to other datasets. Their findings are described in the paper "Hubble Asteroid Hunter III. Physical properties of newly found asteroids".

The team includes members from the European Space Agency (ESA), NASA's Jet Propulsion Laboratory (JPL), Bastion Technologies, the Université Côte d'Azur, the University of Craiova, and the Astronomical Institute of the Romanian Academy. They are led by Pablo García-Martín, a researcher from the Department of Theoretical Physics at the Autonomous University of Madrid (UAM).

In 2019, astronomers from the European Space Astronomy Center's Science Data Center (ESDC) and the European Science and Technology Centre (ESTEC) came together with the world's largest and most famous citizen-science platform (Zooniverse) and Google. They launched the citizen-science project Hubble Asteroid Hunter (HAH) to identify asteroids in archival Hubble data.

The HAH team is composed of 11,482 volunteers who study 37,000 Hubble images spanning 19 years. After providing almost two million identifications, the team was offered a training set for an automated algorithm to identify asteroids based on machine learning. This yielded 1,701 asteroid trails, with 1,031 corresponding to previously unknown asteroids. About 400 of them were below 1,090 feet (1 kilometer) in size.

This novel method can be effectively applied to datasets gathered by other asteroid-hunting observatories, like NASA's Spitzer Space Telescope and Stratospheric Observatory for Infrared Astronomy (SOFIA). Once the James Webb Space Telescope (JWST) accumulates a large enough dataset, it can also apply the same method to its archival data. In the future, the HAH project plans to examine the streaks of previously uncataloged asteroids to examine their orbits, rotation periods, and other properties.