The researchers found more than 1,700 asteroid traces in archived Hubble data for the past 20 years. While many asteroids are already known, more than 1,000 are not. What are another 1,000 asteroids for? Like all asteroids, they could hold valuable clues to the history of the solar system.
As time passes and more and more telescopes make more and more observations, their combined archive data keeps growing. Sometimes discoveries lurk in these data that await new analytical tools or renewed efforts from scientists before they are revealed. That’s what happened in an effort called Hubble Asteroid Hunter.
The astronomers have published 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 junk may be another astronomer’s treasure,” Kruk said in a Press release.
The data they sought was largely overlooked by other non-asteroid-focused observing efforts. In many cases, the data would have appeared as “noise” and was removed to bring out different elements. But all of this unexamined secondary data is still archived and available.
“The amount of data in the astronomy archive is growing exponentially, and we wanted to use this incredible data,” Kruk said.
The project examined more than 37,000 composite Hubble images. They were taken between April 30, 2002 and March 14, 2021 with the Advanced Camera for Surveys and Wide Field Camera 3 aboard the Hubble Space Telescope. Most of the images are 30 minute exposures, so the asteroid trails appear as curved streaks.
The streaks go to the heart of the problem: computers have trouble detecting them. This is where the Zooniverse platform and citizen scientists come in.
“Due to the orbit and motion of Hubble itself, the streaks appear curved in images, making it difficult to classify asteroid trails – or rather, it’s hard to tell a computer how to automatically detect them. “, explained Sandor Kruk.
“Therefore, we needed volunteers to perform an initial classification, which we then used to train a machine learning algorithm.”
Volunteers delivered. 11,482 citizen scientists participated in the image classification. Zooniverse’s Hubble Asteroid Hunter page had more than 2 million clicks, and volunteers provided 1,488 positive ratings in about 1% of images.
The work of the citizens who participated trained a machine learning algorithm to find the rest of the images quickly and accurately. The algorithm exists in Google Cloud, and once it was trained it contributed 900 additional detections for a total of 2487 potential asteroid tracks in Hubble data.
Then the professional scientists played their part. Three of the paper’s authors, including lead author Sandor Kruk, reviewed the results. They ruled out things like cosmic rays and other objects, resulting in 1,701 tracks found in 1,316 Hubble images. About a third of them were known asteroids, leaving 1031 unidentified asteroid trails.
Above: This mosaic consists of 16 different NASA/ESA Hubble Space Telescope datasets studied as part of the Asteroid Hunter citizen science project. Each of these datasets was assigned color based on the temporal sequence of exposures, with blue tones representing the first exposure in which the asteroid was captured and red tones representing the last.
Follow-up observations will confirm how many of them are newly discovered asteroids and determine their orbits. Some of the 1031 will likely go unconfirmed, but the rest will help flesh out our understanding of the asteroid population in our solar system.
These asteroids escaped detection because they are fainter and likely much smaller than most asteroids detected from the ground. This article is the first published under the Hubble Asteroid Hunter project. In later papers, the authors will use the curved shape of asteroid trails to determine their orbits and distances.
All asteroids are remnants of the early days of the solar system, with most dating from before the formation of planets. They are like time capsules of nature, and they preserve the conditions of the primitive system. That’s why astronomers are so interested in it and why we sent spacecraft to collect samples from asteroids like Bennu and Ryugu.
“Asteroids are remnants of the formation of our solar system, which means we can learn more about the birth conditions of our planets,” Kruk explained.
Above This image from the study is a sky map of Solar System Objects (SSOs) identified in archived Hubble images. Blue stars show identified and known asteroids. Orange circles indicate the location of objects for which the team found no association with SSOs. The ecliptic is shown in red. The two gaps in this graph correspond to the galactic plane, which HST did not observe.
More and more researchers are using archival data like this. It’s economical to sift through existing images for new discoveries, and it pays off.
“The use of archival data produced by imagery campaigns whose primary scientific objectives lie outside the solar system is a common practice in asteroid science. Several groups have used various image archives to find and characterize SSO.”
For example, in 2019, researchers used archival imagery from exoplanet surveys to identify more than 1,800 asteroids, with 182 potential new discoveries.
Astronomers want a full understanding of the solar system’s asteroid population because it helps clarify the history of the solar system.
“A detailed description of small solar system bodies places constraints on different solar system formation scenarios, which make concrete predictions about the size and orbital distribution of objects as a function of time,” the authors explain. “In particular, giant planet migrations and collisional cascades have effects on the size and orbital distribution of asteroids that might be detectable with specially designed observational studies.”
But purpose-built surveys are expensive and time-consuming. Observational proposals also face fierce competition from other researchers with other interests.
“We decided instead to produce such a survey from a large archival dataset,” the authors write.
Kruk hinted at things in the data other than asteroids. “But there were other chance discoveries in the archive footage, which we are currently tracking.”
He also said their approach was a game-changer and they intended to use it again.
“Using such a combination of humans and artificial intelligence sifting through large amounts of data is a game-changer, and we will also use these techniques for other future surveys, such as with the Euclid telescope.”
As for the “…other incidental findings…” in the footage, Kruk declined to share what those other findings might be. He told Universe Today that the findings are “…not related to unusual asteroids but to other discoveries in the data. We’ll be reporting them soon in follow-up publications and announcements, so stay tuned.” !”
We certainly will.
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