A New Planet Discovered? Planet 9 Has a Rival -- Meet Planet Y [9:45]

YouTube ^ | October 6, 2025 | NASA Space News

[SunkenCiv]

Astronomers from Princeton may have found evidence of a hidden planet -- Planet Y -- orbiting in the far reaches of the Solar System. Could this be the missing world shaping the Kuiper Belt? Watch to find out. 

A New Planet Discovered? Planet 9 Has a Rival -- Meet Planet Y | 9:45 
NASA Space News | 556K subscribers | 28,062 views | October 6, 2025

 

Chapters: 
00:00 Introduction 
00:38 The Discovery 
03:04 Scientific Importance and Theories 
05:30 Implications and What’s Next 
08:29 Outro 
08:43 Enjoy

[Secret Agent Man]

How about “Myanus”

We already have Uranus...

[metmom]

Pluto is the ninth planet.

[SunkenCiv]

I wholeheartedly agree.

"To Pluto And Far Beyond" By David H. Levy, Parade, January 15, 2006 -- We don't have a dictionary definition yet that includes all the contingencies. In the wake of the new discovery, however, the International Astronomical Union has set up a group to develop a workable definition of planet. For our part, in consultation with several experienced planetary astronomers, Parade offers this definition: A planet is a body large enough that, when it formed, it condensed under its own gravity to be shaped like a sphere. It orbits a star directly and is not a moon of another planet.

The Nine Planets search results

[telescope115]

I see those headlines on those videos, too. They are very sensationalist. They’re a turnoff to me because to me they’re no different than a lot of videos that are really nothing more than click bait and offer no usefulness to my knowledge of the subject matter.

[telescope115]

+1…

[SunkenCiv]

The X was meant to show that an unnamed planet could be out there. That’s kinda been lost. OTOH, X is the Roman numeral for ten, which means, Planet 10 is being looked for. The demotion of Pluto was strictly political and should be ignored. Instead, it’s boilerplate.

[SunkenCiv]

Hosted and executive produced by Golden Globe and Emmy Award-winning actor William Shatner.

Unseen Planet HIDING in our Solar System
The UnXplained: Mysterious Phenomena (S1) | 5:33
HISTORY | 15M subscribers | 81,761 views | June 21, 2024

--> YouTube-Generated Transcript <--
	·	Intro
0:04	·	SHATNER: On the campus of
0:06	·	the California Institute of Technology
0:09	·	a group of experts led by astronomer Mike Brown
0:13	·	is puzzling over some strange data
0:16	·	from outer space
0:17	·	that they can't explain.
0:21	·	BROWN: A few years ago,
	·	The Unseen Planet
0:22	·	a colleague of mine and I,
0:23	·	Konstantin Batygin, he and I were looking at
0:26	·	the orbits of the most distant objects in our solar system.
0:32	·	This vast collection of objects
0:33	·	is very much like the asteroid belt,
0:36	·	but just an icier version further away.
0:41	·	They're out in the same region where Pluto is,
0:43	·	well past Neptune.
0:45	·	And we realized that the ones that go
0:48	·	the furthest away from the sun
0:49	·	all have their orbits pointing off in one direction.
0:54	·	These guys all go off far away,
0:56	·	and it shouldn't be that way.
0:58	·	Unless there's something pulling them with gravity,
1:01	·	it shouldn't happen.
1:04	·	So, Konstantin and I tried to figure out what's going on,
1:06	·	and we made jokes to each other
1:08	·	that, like, "Well, it could be a planet, but that's dumb.
1:11	·	"We know it's not a planet,
1:12	·	"because we know there are
1:14	·	no other planets in our solar system."
1:16	·	SHATNER: The idea that there's an undiscovered planet
1:20	·	in our solar system that could potentially be
1:22	·	a place where life has formed,
1:24	·	sounds too incredible to believe.
1:28	·	But on the other hand,
1:29	·	Mike Brown still couldn't figure out why
1:34	·	objects in space were being pulled in a strange direction.
1:38	·	BROWN: We spent about two years trying to figure out
1:41	·	what else could be causing these things
1:43	·	to be pulled off in this direction,
1:45	·	and we couldn't figure out what it could be.
1:48	·	We realized, "Actually, this planet just
1:51	·	is the only thing that actually makes sense."
1:55	·	We started doing calculations, simulations.
1:57	·	We realized, actually,
1:59	·	if you put a planet out here that's pulling these things way,
2:03	·	it not only explains these objects,
2:04	·	but it explains half a dozen other things that have been
2:08	·	happening in the solar system.
2:10	·	So, I am really quite convinced
2:12	·	that there is a giant planet
2:15	·	still to be found out there at the edge of the solar system.
2:20	·	SHATNER: In February of 2019,
2:22	·	Mike and his colleagues published a groundbreaking paper
2:26	·	in which they proposed that there could be
2:28	·	an unseen planet hiding in our solar system,
2:32	·	which they have dubbed Planet Nine.
2:36	·	Their intriguing theory made headlines,
2:38	·	because for hundreds of years,
2:39	·	humanity has believed that
2:41	·	there were only eight planets in the solar system,
2:44	·	not including Pluto,
2:46	·	which is considered a smaller "dwarf planet."
2:49	·	So, how could there be an undiscovered planet
2:53	·	in our corner of the universe
2:56	·	that we're only now finding out about?
3:00	·	Right now, we think, based on our computer simulations,
3:04	·	that Planet Nine is
3:05	·	about seven times
3:08	·	more massive than the Earth.
3:11	·	And it's 600 times further
3:13	·	than the Earth is from the Sun.
3:16	·	And so it's way out there.
3:20	·	FRANK: Planet Nine, if it exists,
	·	How Could It Exist
3:22	·	it's so far away,
3:23	·	out there in the deep, deep dark,
3:25	·	that it's just very difficult to detect.
3:28	·	You are so far out in the solar system
3:31	·	when you get to these kinds of distances,
3:33	·	that the sun is barely distinguishable.
3:36	·	There's just not a lot of light out there.
3:39	·	But really, it's exciting, because,
3:41	·	even though we can't see the planet,
3:44	·	it's just almost impossible to not to wonder
3:47	·	what is happening out there.
3:50	·	SHATNER: If scientists are able to prove that there is, in fact,
3:54	·	a planet hiding in the darkness of our solar system,
3:58	·	it would raise an even more pressing question.
4:01	·	Could there actually be life
4:04	·	on this mystery planet?
4:07	·	BROWN: Planet Nine is a really important place
4:10	·	to look for life.
4:12	·	Right now, scientists are very strongly focused on
4:15	·	figuring out whether there's just single celled
4:18	·	microbial life on Planet Nine.
4:22	·	Here is the interesting thing about Planet Nine
4:24	·	when it comes to life.
4:26	·	It's possible that if Planet Nine exists,
4:29	·	that it was much closer in the solar system earlier on.
4:32	·	And if it had a rocky surface,
4:35	·	and if it was in the places where liquid water could exist,
4:39	·	then maybe it did form microbial life.
4:43	·	And then maybe, somehow, it got
4:45	·	kicked out farther out from there.
4:50	·	BROWN: One of the things that
4:51	·	we don't know about Planet Nine is
4:54	·	why do we have this planet so far away?
4:57	·	I think the most likely hypothesis
5:00	·	is that, as it was going around the sun,
5:02	·	it got too close.
5:05	·	And as you get too close, you get a, basically,
5:07	·	a gravitational slingshot, and you go whizzing out
5:09	·	to the outer part of the solar system.
5:12	·	And it's been out there basically lurking around,
5:16	·	waiting for us to find it ever since then.

[SunkenCiv]

reprocessed transcript using https://app.textformatter.ai/

Planet Y: The Search for a New World in Our Solar System

Introduction

Astronomers may have found evidence of a new planet hiding in our solar system. And it’s not planet 9. A recent study from Princeton University proposes the existence of planet Y, a smaller, closer world that could be subtly bending the orbits of distant Kuiper Belt objects. If proven, it would be the first new planet added to our solar system since Neptune. In this video, we’ll explore what planet Y is, why scientists think it might exist, and what comes next in the search for it. Let’s get started.

The Discovery

The idea of hidden planets isn’t new. For more than a century, astronomers have speculated that unseen worlds beyond Neptune could explain odd movements among distant bodies. Pluto’s discovery in 1930 briefly satisfied that curiosity, but as observations improved, its small mass proved inadequate to explain the remaining anomalies. Now, new data suggests there could be more out there. In August 2025, Princeton astrophysicists Amir Siraj, along with Christopher Chiba and Scott Tmaine, published a peer-reviewed study in Monthly Notices of the Royal Astronomical Society proposing planet Y, a hypothetical planet orbiting between 100 and 200 astronomical units (AU) from the sun. The researchers analyzed the orbits of more than 150 Kuiper Belt objects (KBOs).

After accounting for Neptune’s influence, they noticed something unusual. The orbital planes of objects between 80 and 200 astronomical units are systematically tilted. This warp is small but statistically significant, hinting at the pull of a massive unseen body. To explain it, the team modeled multiple scenarios: gravitational resonance among the KBOs, the Milky Way’s tidal influence, and past stellar flybys. None could reproduce the observed pattern as effectively as a single orbiting planet.

Their calculations suggest a body 25 to 450 times the mass of Pluto, roughly between Mercury and Mars in size, orbiting on a path inclined 10 to 15° relative to the solar system’s main plane. That makes it smaller and closer than the much-discussed planet 9, which is predicted to be 5 to 10 Earth masses and roughly 600 astronomical units away. So far, no telescope has directly seen planet Y. The evidence is entirely gravitational, a mathematical fingerprint written in the Kuiper Belt’s architecture. Yet, this pattern is precise enough that many astronomers now view the hypothesis as a credible, testable prediction rather than speculation.

Scientific Importance and Theories

If planet Y exists, it would challenge the assumption that our solar system’s planetary family ends with Neptune. Its presence would imply that the early solar system produced more large bodies than previously thought, some of which survived on distant orbits. There are three leading formation scenarios: One, native survivor, a planet formed near the giant planets and was scattered outward during the solar system’s chaotic early evolution. Two, captured object, a wandering interstellar planet that passed close enough to the sun to be gravitationally trapped. Three, complement to planet 9, a smaller companion that together with planet 9 shapes the Kuiper Belt structure. Each explanation would add a new layer to models of planetary formation and migration. Planet Y’s predicted mass is also scientifically significant.

A body with a fraction of Earth’s mass at 100 to 200 astronomical units would have enough gravity to clear its orbit, the core requirement for official planet status under the International Astronomical Union’s 2006 definition. At roughly 50 times Pluto’s mass, it would easily qualify as a full planet, not a dwarf one. Confirming such a world would also refine our understanding of the Kuiper Belt’s dynamics. The belt is not uniform. Its objects exhibit clustered angles and inclinations that suggest an external perturbing force. Planet Y could provide a straightforward gravitational explanation for this pattern. Not all astronomers are convinced.

Some argue that the apparent warp could emerge naturally from the collective gravitational effects of many smaller objects. Others point out that small number statistics and observational bias might exaggerate the alignment. Nevertheless, the Princeton model reproduces observed data with fewer assumptions, keeping the hypothesis scientifically persuasive. If real, planet Y would fill an important missing link, showing that planetary formation continues smoothly into the outer regions rather than stopping abruptly after Neptune. In broader terms, it would remind us that even within our own solar system, much remains undiscovered.

Implications and What’s Next

The key test for planet Y will come from observation. The Vera Rubin Observatory in Chile, set to begin full operations soon, is designed for this exact kind of search. Its Legacy Survey of Space and Time (LSST) will image the entire southern sky every few nights, capturing faint, slow-moving objects at the fringes of the solar system. At 100 to 200 astronomical units, planet Y would be extremely dim, perhaps a million times fainter than what the naked eye can see, and moving only a few arcseconds. But LSST’s repeated scans and powerful data processing algorithms could reveal its motion over months or years. If planet Y exists, LSST might detect it directly or indirectly through improved mapping of distant KBOs whose orbits betray its gravitational tug.

In either case, the data collected within the next few years should decisively confirm or reject the hypothesis. Should the planet be found, the implications are profound. It would represent the first new planet discovered in nearly two centuries and confirm that our solar system extends much farther and with greater complexity than previously imagined. It could explain why certain long-period comets approach the sun from odd directions, and it would add a new data point for studying how planetary systems form and evolve elsewhere in the galaxy. The discovery would also settle an ongoing public debate about what defines a planet. Pluto was reclassified as a dwarf planet because it hadn’t cleared its orbit. A Mars-mass world at 100 astronomical units would have no such problem, satisfying every criterion of planethood and restoring some symmetry to the solar system’s outer architecture.

If, however, the LSST finds no trace of planet Y, the outcome remains valuable. Astronomers would re-evaluate the dynamics of the Kuiper Belt, perhaps attributing its warp to distributed mass effects or past stellar encounters. The search itself will yield thousands of new minor body discoveries, refining our map of the solar system’s edge. Looking ahead, planet Y has already sparked discussions about future deep space missions. With advancements in propulsion, future probes might travel beyond Neptune to directly survey these distant realms, whether or not a hidden planet awaits there. The broader takeaway is that science progresses through investigation, not certainty. Each anomaly drives inquiry, and even a null result pushes knowledge forward.

Outro

Planet Y remains unconfirmed, but the search continues. Whether it exists or not, the investigation expands our understanding of the solar system’s edge. Sometimes the pursuit of discovery reveals as much as discovery itself.