Over a hundred distant asteroids discovered - trans-Neptunian objects

[lpetrich]

They were discovered with the help of the Dark Energy Survey - Home - The Dark Energy Survey - a project to map a part of the sky to observe distant galaxies and supernovae. This was to find the overall distribution of matter in the observable Universe, something with clues for primordial fluctuations, dark matter, and dark energy.

This survey also found a sizable number of Trans-Neptunian Objects - distant asteroids.

Researchers find new minor planets beyond Neptune - phys.org
Astronomers Just Found More Than 100 Minor Planets at The Edge of Our Solar System - sciencealert.com
noting
Trans-Neptunian Objects Found in the First Four Years of the Dark Energy Survey - IOPscience

They were discovered by searching for anything that moved relative to the stars and galaxies, accepting only what was observed several times.

From phys.org:

After many months of method-development and analysis, the researchers found 316 TNOs, including 245 discoveries made by DES and 139 new objects that were not previously published. With only 3,000 objects currently known, this DES catalog represents 10% of all known TNOs. Pluto, the best-known TNO, is 40 times farther away from the sun than Earth is, and the TNOs found using the DES data range from 30 to 90 times Earth's distance from the sun. Some of these objects are on extremely long-distance orbits that will carry them far beyond Pluto.

Now that DES is complete, the researchers are rerunning their analysis on the entire DES dataset, this time with a lower threshold for object detection at the first filtering stage. This means that there's an even greater potential for finding new TNOs, possibly as many as 500, based on the researchers' estimates, in the near future.