A set of 632 main-belt asteroids (178 previously known and 454 unknown objects) has been identified in the archival images from the NASA/ESA Hubble Space Telescope. Citizen scientists from around the world contributed to the identification of this asteroid bounty. Professional astronomers combined the volunteers’ efforts with machine learning algorithm to identify the asteroids.

This Hubble image of the barred spiral galaxy UGC 12158 looks like someone took a white marking pen to it. In reality it is a combination of time exposures of a foreground asteroid moving through Hubble’s field-of-view, photobombing the observation of the galaxy. Several exposures of the galaxy were taken, what is evidence in the dashed pattern. The asteroid appears as a curved trail due to parallax: because Hubble is not stationary, but orbiting Earth, and this gives the illusion that the faint asteroid is swimming along a curved trajectory. The uncharted asteroid is in inside the asteroid belt in our Solar System, and hence is 10 trillion times closer to Hubble than the background galaxy. Image credit: NASA / ESA / Hubble / Pablo García Martín, UAM / Joseph DePasquale, STScI / Alex Filippenko, UC Berkeley.

Over 4 billion years ago, the eight major planets around our Sun formed by sweeping up debris from a vast disk of dust and gas surrounding the Sun.

This is common to the planet birthing process, and the NASA/ESA Hubble Space Telescope was the first to optically see similar disks surrounding newborn stars, providing a peek into the Solar System’s formative years.

Now, 4 billon years later, the planet construction yard is still cluttered with leftover debris.

Most of this ancient space rubble — asteroids — can be found between the orbits of Mars and Jupiter within the main asteroid belt.

“We are getting deeper into seeing the smaller population of main belt asteroids,” said Dr. Pablo García Martín, an astronomer at the Autonomous University of Madrid.

“We were surprised with seeing such a large number of candidate objects.”

“There was some hint of this population existing, but now we are confirming it with a random asteroid population sample obtained using the whole Hubble archive.”

“This is important for providing insights into the evolutionary models of our Solar System.”

Because of Hubble’s fast orbit around the Earth, it can capture wandering asteroids through their telltale trails in the Hubble exposures.

As viewed from an Earth-based telescope, an asteroid leaves a streak across the picture.

Asteroids ‘photobomb’ Hubble exposures by appearing as unmistakable, curved trails in the photographs.

As Hubble moves around the Earth, it changes its point of view while observing an asteroid, which also moves along its own orbit.

By knowing the position of Hubble during the observation and measuring the curvature of the streaks, scientists can determine the distances to the asteroids and estimate the shapes of their orbits.

The asteroids snagged mostly dwell in the main belt, which lies between the orbits of Mars and Jupiter.

Their brightness is measured by Hubble’s sensitive cameras. And comparing their brightness to their distance allows for a size estimate.

The faintest asteroids in the survey are roughly one forty-millionth the brightness of the faintest star that can be seen by the human eye.

“Asteroid positions change with time, and therefore you cannot find them just by entering coordinates, because at different times, they might not be there,” Dr. Merín said.

“As astronomers we don’t have time to go looking through all the asteroid images.”

“So we got the idea to collaborate with over 10,000 citizen-science volunteers to peruse the huge Hubble archives.”

The results appear in the journal Astronomy & Astrophysics.


Pablo García-Martín et al. 2024. Hubble Asteroid Hunter III. Physical properties of newly found asteroids. A&A 683, A122; doi: 10.1051/0004-6361/202346771

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