Citizen scientists spot more than 1,000 new asteroids in old Hubble Telescope photos

hubble space telescope of a spiral galaxy in deep space, with a dotted line near its top indicating the trail of an asteroid in our own solar system
This Hubble Space Telescope 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. The asteroid appears as a curved trail due to parallax: Because Hubble is not stationary but orbiting Earth, 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, Pablo García Martín (UAM); Image Processing: Joseph DePasquale (STScI); Acknowledgment: Alex Filippenko (UC Berkeley))

The dotted white streak cutting across this photo of a faraway galaxy might seem like a nuisance for astronomers, but it's actually the mark of a previously undiscovered asteroid.

The image, snapped by the Hubble Space Telescope from its decades-long perch in low Earth orbit, is one of many that have been photobombed by asteroids whizzing in front of the telescope's eyes. A large group of citizen scientists poring over such old Hubble photos has discovered more than 1,000 previously unknown space rocks that reside in the main asteroid belt between Mars and Jupiter, hundreds of them less than 0.6 miles (1 kilometer) wide, NASA announced on Thursday (April 18).

"We are getting deeper into seeing the smaller population of main belt asteroids," Pablo García Martín of the Autonomous University of Madrid in Spain said in a NASA statement

"We were surprised with seeing such a large number of candidate objects," he added. "This is important for providing insights into the evolutionary models of our solar system."

Related: The best Hubble Space Telescope photos of all time

The newfound asteroids help refine the census of main belt asteroids, which is already estimated to be over a million. And some of the newly discovered objects are likely fragments of larger space rocks that broke apart due to collisions, researchers said.

The asteroid trails appear curved in Hubble photos because the telescope changes its point of view as it moves in Earth orbit. To find these trails, scientists stitched together multiple long-exposure shots, which explains the white dashed line. Spotting these telltale signs in deep-sky images is a tough task. Often, the pictures are cluttered with streaks by satellites, cosmic rays and other artifacts confusingly similar to asteroid trails.

"Asteroid positions change with time, and therefore you cannot find them just by entering coordinates, because at different times, they might not be there," Bruno Merín, of the European Space Astronomy Centre in Spain, said in the same statement. "As astronomers, we don't have time to go looking through all the asteroid images."

The researchers picked more than 37,000 Hubble photos spanning the past two decades and virtually cut them into four portions. Then, they turned to more than 10,000 volunteers from around the world to inspect the images and flag those with potential asteroid trails. Two million identifications later, the team found 1,701 asteroid trails, of which 1,031 were previously uncatalogued. The work also flagged 45 objects as potential comets.

The findings are described in a paper published last month in the journal Astronomy and Astrophysics.

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Sharmila Kuthunur contributor

Sharmila Kuthunur is a Seattle-based science journalist covering astronomy, astrophysics and space exploration. Follow her on X @skuthunur.

  • Classical Motion
    If we were to stop taking images today, it would take decades just to view previous images(data) that no one has looked at yet. Much of new findings we read about today, come from old data, that is processed in a different manor. Many will spend their lifetimes analyzing old data.

    There is a hope that A.I. can analyze this backlog and perhaps glean much more from it. If we can trust it.

    But on a more serious note, an unseen rock is our greatest present danger. But most have other hobbies.

    Movies about rocks hitting earth are not funny. Bullets kill.
  • blazeww20
    So. Maybe they need to just give stuff to citizen scientists... cause how do official scientists miss that many for years....
  • COLGeek
    There have been efforts in the past to get humans to help with similar data. As @Classical Motion indicated, there is hope that AI will mature to sift through this sort of visual data, but to date the human eye-brain effectiveness is hard to beat in some applications.