Over 100 Minor Planets Have Been Discovered at the Edge of the Solar System

Astronomers have identified nearly 140 previously unknown minor planets in the outer reaches of the solar system beyond the orbit of Neptune.

An international team of researchers analyzed four year's worth of data collected by the Dark Energy Survey (DES)—an astronomical project aimed at investigating the dynamics of the universe's expansion by imaging the southern sky.

The DES wasn't designed specifically to look for objects such as minor planets, however, the data it has gathered has proven to be especially useful for this task. Minor planets are any astronomical object in orbit around the Sun which are not fully-fledged planets or comets—for example, dwarf planets or asteroids.

According to a study published in The Astrophysical Journal Supplement Series, researchers identified a total of 316 objects beyond the orbit of Neptune, referred to as trans-Neptunian objects (TNOs)—139 of which had not been documented before. These objects are located between around 30 to 90 astronomical units (equivalent to the the Earth-Sun distance) from the Sun.

In total scientists know of only about 3,000 TNOs—ranging from small asteroids and comets to dwarf planets—so the objects identified in the latest study represent about 10 percent of the total. The best known and largest of these TNOs is the dwarf planet Pluto, which is located around 40 astronomical units away from the sun.

For the latest study, the researchers used new techniques to identify the TNOs in the first four years of the DES data. Unlike traditional surveys aimed at looking for TNOs—which take very frequent measurements of the sky—DES was designed to observe large, distant objects such as stars, galaxies and supernovae. So the scientists had to adapt their approach.

"Dedicated TNO surveys have a way of seeing the object move, and it's easy to track them down," Pedro Bernardinelli, an author of the study from the University of Pennsylvania, said in a statement. "One of the key things we did in this paper was figure out a way to recover those movements."

Cerro Tololo Inter-American Observatory
The Cerro Tololo Inter-American Observatory in Chile where the Dark Energy Survey operates from. Fermilab

Using computer software, the team began their analysis by examining seven billion "dots" which algorithms identified as representing astronomical objects of different varieties. They then narrowed this down to around 22 million dots, by removing any which appeared to remain in the same location over multiple nights. These were likely to be objects such as stars, galaxies and supernova.

The researchers then determined which of these 22 million dots appeared on six subsequent nights of observation, reducing the number further to around 400 candidates. And finally, they whittled down these 400 candidates to 316 confirmed TNOs using further verification techniques.

According to the scientists, the TNOs they have catalogued could help to shed light on some of the universe's mysteries, such as the potential existence of a hypothetical world tens of millions of miles from the sun known as "Planet Nine" or "Planet X."

The possible presence of this planet was first proposed by two scientists in 2016 who said that it could explain the unusual, highly elliptical orbits of a cluster of TNOs. The scientists argued that normal models of solar system dynamics cannot explain this strange collection of orbits. However, to date no direct evidence of Planet Nine has emerged.

The Dark Energy Survey began imaging the southern sky in August 2013 and finished collecting data after six years at the beginning of 2019. The main goal of the project was to investigate the nature of dark energy—a mysterious, hypothetical form of energy causing the accelerated expansion of the universe.

The survey used the 520-megapixel Dark Energy Camera—based at the National Science Foundation's Cerro Tololo Inter-American Observatory in Chile—to record data from more than 300 million galaxies.

Over 100 Minor Planets Have Been Discovered at the Edge of the Solar System | Tech & Science