Over 1,700 asteroid traces have been discovered in Hubble data over the previous 20 years, according to researchers. While many of the asteroids have been discovered before, over 1,000 have not. What useful are 1,000 more asteroids? They, like other asteroids, may contain important information about the Solar System’s past.
As more telescopes conduct more observations throughout time, the total amount of archived data continues to expand. Sometimes, new analysis methods or renewed efforts from scientists are required to disclose insights hidden in the data. That’s what happened with the Hubble Asteroid Hunter project.
In 2019 a group of astronomers launched the Hubble Asteroid Hunter. It’s a citizen science project on the Zooniverse platform. Their goal was to comb through Hubble data to find new asteroids.
The astronomers released the results of their project in a new paper titled Hubble Asteroid Hunter I. Identifying asteroid trails in Hubble Space Telescope images. The study is online in the journal Astronomy and Astrophysics. The lead author is Sandor Kruk from the Max Planck Institute for Extraterrestrial Physics.
“One astronomer’s trash can be another astronomer’s treasure,” Kruk stated in a press release.
The information they were looking for had mostly been discarded from other observational projects that weren’t focused on asteroids. The data would have looked as “noise” in many situations, thus it was deleted to make the distinct pieces stand out. However, all of this unanalyzed secondary data is still kept and accessible.
“The amount of data in astronomy archives increases exponentially, and we wanted to make use of this amazing data,” said Kruk.
The team looked at almost 37,000 Hubble composite pictures. They were collected using the Hubble Space Telescope’s Advanced Camera for Surveys and Wide Field Camera 3 between April 30, 2002, and March 14, 2021. Asteroid trails appear as curving streaks in most photographs because they are 30-minute long exposures.
The streaks are at the root of the problem: computers have a hard time detecting them. The Zooniverse platform and citizen scientists can help with this.
“Due to the orbit and motion of Hubble itself, the streaks appear curved in the images, which makes it difficult to classify asteroid trails – or rather it is difficult to tell a computer how to automatically detect them,” Sandor Kruk noted.
“Therefore, we needed volunteers to do an initial classification, which we then used to train a machine-learning algorithm.”
The volunteers delivered.The photos were classified by 11,482 citizen scientists. Over 2 million people visited Zooniverse’s Hubble Asteroid Hunter page, and volunteers submitted 1488 positive classifications in roughly 1% of the photos.
The citizens’ efforts trained a machine-learning system to swiftly and reliably search the remaining photos. The program is hosted on Google Cloud, and after trained, it added another 900 detections to the Hubble data, totaling 2487 probable asteroid tracks.
Then came the professional scientists’ turn. The findings were discussed by three of the paper’s authors, including main author Sandor Kruk. They took out stuff like cosmic rays and other objects, leaving 1701 traces in 1316 Hubble photos. There were 1031 unexplained asteroid tracks, with around one-third of them being known asteroids.
Follow-up observations will establish how many are newly found asteroids and their orbits. Some of 1031’s findings are unlikely to be validated, but the remainder will add to our knowledge of the asteroid population in our Solar System.
Because these asteroids are fainter and possibly smaller than most asteroids spotted from the ground, they have avoided detection. This is the first publication to come out of the Hubble Asteroid Hunter project. The authors will utilize the curved form of the asteroid trails in future articles to calculate their orbits and distances.
All asteroids are relics from the early days of the Solar System, usually from before the planets formed. They act as time capsules for the early system, preserving the circumstances there. That is why astronomers are so fascinated by them, and why missions have been launched to retrieve samples from asteroids like Bennu and Ryugu.
“The asteroids are remnants from the formation of our Solar System, which means that we can learn more about the conditions when our planets were born,” Kruk explained.