Planet X could be a dwarf planet

Solar system: pair of boulders compete with Pluto

At the edge of our solar system, two boulders defy the eternal cold together. The two celestial bodies are 180 and 138 kilometers in size and orbit each other at a distance of just 350 kilometers, according to astronomers working with Rodrigo Leiva from the US Southwest Research Institute in the Planetary Science Journal. The couple drifts around the sun in an elliptical orbit, the shape and size of which is roughly comparable to that of Pluto, which is 2,300 kilometers in size.

The duo with the catalog number (523764) 2014 WC510 is one of the "trans-Neptunian" objects: What is meant are asteroids or dwarf planets that are further away from the sun than Neptune, the outermost of the eight known planets in the solar system. Astronomers know several thousand of these ice-cold chunks so far. However, little more is known about many than that they exist.

Until recently, this also applied to WC in 2014510. The object was already noticed on telescope images in 2011, but researchers initially thought it was a single asteroid. That only changed in December 2018, when WC moved in 2014510 seen from the earth in front of a binary star system. Six smaller observatories in the USA not only observed a brief darkening of the light source in the background, but also two closely successive drops in brightness. This fits best with the scenario that not a single, but two separate celestial bodies have moved through the field of vision, the researchers write in their specialist article.

The telescopes involved are part of a citizen science project called RECON, in which committed amateur astronomers hunt down trans-Neptunian objects on the Pacific coast. The professional team of astronomers led by Rodrigo Leiva then took over the demanding data analysis.

Pairs of celestial bodies don't seem unusual on the edge of the solar system. This was not least shown by the images of the New Horizons space probe. It flew past Pluto in July 2015 and passed the more outlying trans-Neptunian object Arrokoth on New Year's Day 2019. It consists of two boulders that collided at some point in the distant past and have stuck together ever since.

2014 toilet510 however, appears to belong to a different weight class than the snowman-shaped, 38-kilometer-long Arrokoth. The two boulders that have now been discovered are between three and five times as large. In addition, they are not so far from the sun: The duo in 2014 WC510 at times it approaches up to 4.3 billion kilometers (experts speak of 29 astronomical units), which is just within the orbit of Neptune.