doi.org/10.48550/arXiv.2505.15806
Credibility: 888
#Kuiper
In the cold, distant regions of the Solar System, far beyond Pluto, astronomers have just identified what may be a new dwarf planet
Called 2017 OF201, this rocky object is about 700 kilometers in diameter, which is large enough to be considered a dwarf planet.
What makes this discovery even more interesting is its orbit, which suggests that the mysterious “Planet Nine,” a supposedly large planet hidden in the darkest and most distant regions of the Solar System, may not exist.
“This object’s orbit is very elongated.
The farthest point from the Sun, called aphelion, is more than 1,600 times the distance between Earth and the Sun.
The closest point, called perihelion, is 44.5 times that distance, similar to the orbit of Pluto,” explains Sihao Cheng, an astrophysicist at the Institute for Advanced Study in Princeton, USA.
Cheng and his team are searching for trans-Neptunian objects (TNOs), which are chunks of rock and ice that orbit the Sun beyond Neptune, about 30 astronomical units away (an astronomical unit is the distance between Earth and the Sun).
Finding these objects is difficult because they are very small, very far from the Sun, extremely cold and reflect little light.
In recent years, more powerful telescopes have been able to better observe the Kuiper Belt and even more distant areas, allowing the discovery of individual objects.
The most distant object ever found is FarFarOut, a rock about 400 kilometers across that was detected at 132 astronomical units.
Researchers discovered 2017 OF201 by analyzing old data collected by the Dark Energy Camera Legacy Survey (DECaLS) and the Canada-France-Hawaii Telescope (CFHT).
Between 2011 and 2018, these instruments observed 2017 OF201 a total of 19 times, allowing the team to study the object and its orbit with great precision.
2017 OF201 was first seen at 90.5 astronomical units, more than twice the orbital distance of Pluto, which is about 40 astronomical units.
Its orbit is a very elongated ellipse, reaching 44 astronomical units at its closest point to the Sun and extending out to 1,600 astronomical units, reaching the inner Oort Cloud, a region of rock and ice that surrounds the Solar System at its outermost limits.
We still don’t know how this orbit, which takes 25,000 years to complete, came to be.
It could be that 2017 OF201 underwent a gravitational interaction with something large that altered its trajectory, or that its orbit evolved in stages over time.
What is clear is that this orbit is very different from the clustered orbits of other previously discovered trans-Neptunian objects, which some astronomers believed to be evidence of a large planet hidden in the Solar System.
The team ran simulations of 2017 OF201‘s orbit, with and without the presence of Planet Nine.
They found that without Planet Nine, 2017 OF201 could maintain a stable orbit for a long time, as it does today.
But with Planet Nine, gravitational interactions with Neptune would cause 2017 OF201 to be ejected from the Solar System in less than 100 million years.
This is some of the strongest evidence yet against the existence of Planet Nine.
What’s more, the discovery suggests that there may be many other objects like it in the Kuiper Belt and beyond that we haven’t found yet.
“2017 OF201 spends only 1 percent of its orbital time close enough to be detected.
The existence of this single object suggests that there may be about a hundred other objects with similar orbits and sizes, but they are too far away to be seen right now,” Cheng says.
“Despite advances in telescopes that allow us to explore distant parts of the universe, there is still much to discover about our own Solar System.”
2017 OF201 was officially announced by the International Astronomical Union and described in a paper available on the preprint site arXiv.
Published in 05/25/2025 16h45
Text adapted by AI (Grok) and translated via Google API in the English version. Images from public image libraries or credits in the caption. Information about DOI, author and institution can be found in the body of the article.
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