Resembling various sizes of rocks scattered across a terrain, asteroids exhibit a wide range of dimensions as they travel along their orbits around the Sun, making their cataloging in space a challenging task due to their faint appearance and constant motion, preventing them from are easily captured in photographs. Recently, astronomers used an extensive collection of archived images from NASA’s Hubble Space Telescope to visually detect an unnoticed group of smaller asteroids in motion. This extensive search involved the meticulous examination of 37,000 Hubble images captured over a 19-year period, resulting in the identification of 1,701 asteroid tracks, of which 1,031 were previously undocumented asteroids. Remarkably, about 400 of these uncatalogued asteroids are less than 1 kilometer in size.
The identification of this abundant asteroid population was made possible by the collaborative efforts of volunteers around the world, commonly called “citizen scientists.” These volunteers, in conjunction with a machine learning algorithm, helped professional scientists identify and categorize the asteroids in the images. This innovative method of discovering asteroids in astronomical archives dating back decades has the potential for effective application in other datasets, as highlighted by the researchers involved in the study.
Lead author Pablo García Martín from the Autonomous University of Madrid, Spain, expressed his surprise at the depth of observation achieved regarding smaller main-belt asteroids, emphasizing the unexpected discovery of a substantial number of candidate objects. Martín mentioned that although there were some indications of the existence of this asteroid population, the current findings from a random sample derived from the entire Hubble archive confirm its presence, providing valuable information about the evolutionary patterns of our solar system.
The extensive and diverse sample of asteroids identified offers valuable new insights into the formation and progression of the asteroid belt. The prevalence of small asteroids supports the notion that they are fragments resulting from the collision and fragmentation of larger asteroids, similar to broken pottery, a gradual process that unfolds over billions of years. An alternative hypothesis proposes that these smaller fragments originated in their current form billions of years ago, but the absence of a plausible mechanism that prevents their aggregation and growth into larger sizes, accumulating dust from the planet-forming disk around the Sun, raises questions. . Co-author Bruno Merín, from the European Center for Space Astronomy in Madrid, Spain, indicated that collisions between asteroids should leave distinct signatures that can be used to examine the population in the main belt.
Given Hubble’s fast orbit around Earth, it has the ability to capture the movement of drifting asteroids through the distinct tracks they leave in Hubble images. When observed from a ground-based telescope, the presence of an asteroid is marked by a visible band in the image, with asteroids often inadvertently appearing in Hubble displays as curved trails recognizable in photographs.
As the Hubble Space Telescope orbits Earth, it undergoes a continual shift in perspective as it observes asteroids, which follow their own orbital paths. Scientists use knowledge of Hubble’s position during observation and analyze the curvature of the tracks to determine the distances to these asteroids and make estimates about the shapes of their orbits. Most of these asteroids reside in the main belt located between the orbits of Mars and Jupiter, and their luminosity is quantified using Hubble’s sophisticated cameras. By correlating their brightness with distance, researchers can approximate the size of these celestial objects. The dimmer asteroids identified in the survey exhibit a luminosity that is approximately one forty-millionth of that of the faintest star visible to the naked eye.
Merín highlighted: “The positions of the asteroids exhibit temporal variations, making it impossible to locate them just by entering coordinates, as their positions may not align in different instances.” Due to time constraints, astronomers are unable to manually filter through all images of the asteroid. Therefore, a new approach was devised to involve more than 10,000 citizen science volunteers in searching Hubble’s vast archives for asteroid identification.
In 2019, an international consortium of astronomers started the Hubble Asteroid Hunter project, a citizen science venture that aims to identify asteroids in archival Hubble data. The venture was formulated by experts and technicians from the European Science and Technology Center (ESTEC) and the scientific data center of the European Space Astronomy Center (ESDC), in partnership with the Zooniverse platform, the largest and most widely adopted science platform citizen globally, together with Google.
A substantial cohort of 11,482 citizen science volunteers actively participated and contributed nearly 2 million identifications, subsequently receiving a training dataset for an automated algorithm to recognize asteroids using artificial intelligence. This innovative methodology is promising for potential application to diverse data sets.
The next phase of the project involves examining tracks attributed to previously unidentified asteroids to delineate their orbits and investigate various characteristics such as their rotation periods. Given that most of these asteroid tracks were captured by Hubble several years ago, it is currently infeasible to perform follow-up observations to determine their orbital parameters.
Source:
https://hubblesite.org/contents/news-releases/2024/news-2024-014.html
