Evidence of controversial Planet 9 uncovered in sky surveys taken 23 years apart

[AIPedant]

I think “15 times further from the Sun than Pluto” is more meaningful for most readers than “700 times further from the Sun than Earth.” If it exists, it’s way way way out there.

[NikkiA]

I dunno, '700 AU' gelled for me instantly, '15 times the distance to pluto' doesn't even make sense given pluto's orbit isn't anywhere near circular.

[ck2]

There's an episode on "Space & Beyond" where they show all the planets in scale to the realworld on an actual football field.

Then to show Planet 9 distance they have to get in a car and drive a few miles.

That worked for me.

[nine_k]

700 AU is way past heliopause, firmly in the interstellar space. Same, 15 times farther than Pluto is definitely away from the Solar system "proper". It's about 100 light-hours away from Sun.

I wonder how could this object be counted as a "planet" belonging to the Solar system, even if it were the size of Jupiter. But it's an object "estimated to be 2 to 4 times the radius, and about ten times the mass of the Earth". This must be another class of celestial bodies, some jumbo-sized Oort cloud object.

[1970-01-01]

Yes, also being 10x the mass of Earth that far out hints that it may be an interstellar object captured by the Sun.

[bsdetector]

Would this be far enough out to use the sun's gravitational lensing to image distant planets?

It seems like the idea was to send a bunch of instruments way out and then take pictures in the brief time they were at a useful distance, but if there's a planet out there we can orbit and so stop the instruments at that distance it seems like we could make a permanent super telescope.

[carbocation]

All 3 points (two from you and one from '8bitsrule) helped me contextualize this:

* 700 times further from the Sun than the Earth

* 15 times further from the Sun than Pluto

* 0.01 lightyear, or 1/400th the distance to the nearest star

[StopDisinfo910]

But then why Pluto rather than Eris which is considerably further than Pluto or Sedna which is even further?

Pluto is a fairly unremarkable dwarf planet. I don’t think it really helps to compare things to it.

[AzzyHN]

Most readers probably know Pluto is the... well... it's not the farthest dwarf planet. But they know it's far, but don't realize just how far it is. I certainly didn't until I watched a video about it.

700 further from the Sun than Earth is tangible as "really really far" though.

[rainsford]

It's sort of amazing to me that the Sun can capture objects that far away. Like obviously even at that distance the Sun would be by far the closest massive thing, but it's hard to comprehend the effects of gravity being strong enough at that distance. From "Planet 9" the Sun probably wouldn't significantly stand out from all the other stars in the sky, yet you'd be orbiting it.

[8bitsrule]

That IS better, but I like ~0.011Ly too ... the nearest star is about 4Ly away.

Another perspective on the size of the solar system, like the Pale Blue Dot.

[SecretDreams]

I think both work. The average reader doesn't need to conceptualize these distances. They just need to know they're reallllly far away and realllllllly realllllllly (9x) far away. You can use the earth or pluto distances as relative scales.

[smolder]

I think both comparisons together paint a good picture: 15 times further than Pluto, which itself has an orbit ranging from 30 to 49 AU (the distance between Earth and the sun.)

[interludead]

Most people have at least a vague sense of Pluto being the edge of the solar system, so hearing that Planet Nine could be way beyond that makes it feel almost interstellar

[snthpy]

I agree. Idk now many AUs Pluto is but I know it's far away and hardly visible until we flew by.

[mbfg]

how about 4 times further than Voyager 1?

[randomtoast]

I find one theory regarding Planet 9 especially interesting, and that is that it could be a primordial black hole with a Schwarzschild radius on the order of just a few centimeters. So basically, just a golf ball-sized black hole. This would explain why we can see the gravitational effects on the other objects as described in many papers, and it would also explain at the same time why we have no direct observation of this object, because it's simply too tiny and black.

[api]

I really hope this is true, because it would mean there is a black hole close enough it could be examined and studied. This might allow us to test physics ideas that can’t be tested any other way, and maybe even to “finish” physics.

It could also allow gravity and Oberth effect acceleration of small probes to meaningful fractions of the speed of light for interstellar flyby missions. Imagine the Oberth effect boost from thrusting in such a deep gravity well.

[snowwrestler]

This paper exploring the idea has as Fig 1. a to-scale illustration of a 5-Earth-mass primordial black hole:

https://arxiv.org/pdf/1909.11090

As I recall, it did not get printed this way because the ink would be too expensive, or mess with the paper.

[ajross]

FWIW, the object in the linked article is visible, so while that's an interesting theory it's actually ruled out if this thing turns out to be a planet. The black hole would need to be Planet 10 I guess.

[lazide]

At the distances described, available passive light flux is so low, it could be 100% painted with white titanium dioxide paint and we’d be lucky to ever see it. It doesn’t need to be a black hole to be effectively invisible.

[Projectiboga]

If it were earth mass it would be ~grapefruit size. This estimate puts object nine at 9 earth mass so maybe vollyball size or melon size? https://www.astronomy.com/science/is-planet-nine-a-black-hol...

[goku12]

It would be extremely difficult to observe something that far away from the sun, no matter how voluminous it is. I'm not going to scorn at the idea of a blackhole, but I wonder what process can crush that much mass into such a volume. I don't think it's massive enough to suffer a gravitational collapse.

[interludead]

A golf ball–sized primordial black hole lurking in the outer solar system sounds like pure sci-fi, but it would neatly explain the gravitational weirdness and the lack of visual detection

[deadbabe]

Any chance we could use this black hole as a really powerful slingshot by getting very close right before passing the event horizon and then firing off into space?

[perihelions]

This cannot be evidence of Planet 9 (the Batygin and Brown hypothesis)—it's outright incompatible with it.

https://bsky.app/profile/plutokiller.com/post/3lnqm2ymbd22r

If those two spots are the same object, that object is on a high-inclination orbit; but the pattern the Planet 9 hypothesis explains is only compatible with a low-inclination object.

[rozab]

Isn't this exactly how Pluto was discovered? Due to an innacurate estimate of the mass of Neptune (not corrected until Voyager I think), people were hunting for a large planet to explain the discrepancy. After a bunch of searching they happened to find Pluto, but it was not the Planet X they were looking for. The mass estimates for Pluto were gradually downgraded from many Earth masses to 1/500, which is the true reason it was initially classified as a planet.

[sph]

The guy killed Pluto and still he isn't done :(

Seriously though, is he one of the people responsible for Pluto's demotion to dwarf planet?

[Qem]

Perhaps searching for Planet 9 we went straight to Planet 10. There was another one and we happened to find it first. Or also it could be a nomadic planet undergoing a close encounter with the solar system.

[raverbashing]

Nah, if it is big, and at that distance, and follows an elliptical orbit then yes it will be "Planet 9^W 8"

[interludead]

It's still super interesting if it is a massive trans-Neptunian object, just maybe not that Planet 9

[alex_duf]

700 times further => isn't it farther rather than further?

Non native english speaker here, but last I checked further was a metaphorical distance, when farther was a literal distance. You can push a concept further, but you walk farther right? Or did I miss something?

[iamthemonster]

You speak English too well - you have surpassed English speakers. None of us know the difference between further and further.

[williamdclt]

You’re right in theory, but in practice further is used a lot for literal distance. I don’t think I ever hear farther used at all actually

[stevula]

This is, I think, a learned distinction and not universally observed. I only learned this distinction in university.

[dmos62]

If these words have identical etymology (do they?), then the distinction adds no value, in my eyes.

[K0balt]

I hope this turns out to be wrong. I’m still holding out for a primordial back hole Planet X. That would be soooo cool and unbelievably useful.

[interludead]

Not only would it be insanely cool, it'd give us a once-in-a-lifetime chance to study something that might've formed in the first moments of the universe

[jsbisviewtiful]

Why useful? Considering how hard of a time astronomers are having to simply find it it’s hard to imagine it being easy to study.

[rietta]

My lay scientist feel is still that Pluto is a planet, or at the very least have been grandfathered in. The New Horizons reporting 10 years ago just solidified this in my mind. The geological processes are more telling than having cleared the orbital neighborhood. That would just mean that get far enough out and nothing can be a planet no matter how massive. All that said, this massive of an object that far out is very interesting. It would be a very, very cold out there. Would even a gas giant be a solid at that distance? Are there any geological processes possible?

[bikenaga]

Original paper: https://arxiv.org/pdf/2504.17288

[codethief]

Non-PDF link: https://arxiv.org/abs/2504.17288

[DiogenesKynikos]

They forgot to change the title from "Overleaf Example" in their LaTeX source file.

[rootsudo]

When did Planet X become planet 9? Is it because Pluto was a planet and now no longer is so the X was really a Roman numeral vs a variable (if)?

[xattt]

The article explains that Planet X is a possible explanation for the apparent regularity of mass extinction events. Planet 9 is a separate concept to explain the bunching of Kuiper Belt objects, like Sedna.

[anthk]

Well, 9front guys now have a fancy release name.

[vpribish]

I can clearly see the object as a bright group of pixels in the IRAS image, but I don't see a damn thing at the spot they hilight in the AKARI image. Like, are they kidding or is this a crap article with the wrong image or something?

[sigmoid10]

You'd have to read the actual paper [1] to understand this. It does not appear as a physical source in the plot because of how the dataset works. The image is only for reference regarding the position.

[1] https://arxiv.org/pdf/2504.17288

[_heimdall]

Pluto will always be the 9th planet, I don't care what Neil Degrasse Tyson says.

[ashoeafoot]

is such a excentric orbitting body not like a giant guitar string when it comes to the gravitational influence of "passing bye" solar systems and black holes?

[tiahura]

How can we spot planets in other galaxies when we can’t even be certain how many planets are in our solar system?

[userulluipeste]

It has everything to do with the available means that we have, for now. For the record though, we haven't yet been able to spot planets in other galaxies, just in our own Milky Way. The spotted ones just happened to be there when we decided to look, twice. To spot an astral body properly sized to fit the definition of planet, which we yet suspect to orbit around our own star, we should be lucky enough to look exactly at it and not at something else.

[interludead]

Kinda funny how "Planet X" keeps getting rebranded every generation

[astar1]

it's a Mass Relay

[ForOldHack]

It. Is. Not. A. Planet. Not.

[goku12]

By the same celestial laws that stripped Pluto of its planet label, this one would be a planet. Unless you decide to change the rules again.

[gitroom]

love how nerdy this whole thread gets - so much hot debate for basically a frozen rock way out there. you think we're ever gonna agree on what counts as a planet or is it always just moving goalposts?

[marsten]

This would be a planet by anyone's definition, if it's near the predicted 9 times the mass of the Earth.

By comparison the entire Kuiper belt – including Pluto – is estimated to have a total mass of about 10% of Earth's mass.

[doublerabbit]

Can I move to Planet9? Anywhere is better than this planet.

[Qem]

With current spaceships you would die of old age long before arrival.

[metalman]

we already have a 9'th planet, but due to the greatest pedantic campain of all time, pluto got demoted. Though given the current situation, ha!, that could change.....perhaps the naming commity will get noticed, and be offered a chance to do a deal, and Make Pluto A Planet Again,(MPAPA)

[gus_massa]

If you add Pluto, you must add also Eris and a few more, like 5 or more, and perhaps also Ceres.

Here is a nice graphic that excludes Ceres https://en.m.wikipedia.org/wiki/Dwarf_planet#Population_of_d...

[rini17]

The same happened to Ceres first. To be fair, Make Ceres A Planet Again!

[chess_buster]

Pluto for planet! https://www.planetarium-hamburg.de/en/pluto-for-planet

[brookst]

This is especially important if it turnes out there is a black hole acting as an additional planet, since it justifies the “Planet X” name.

[rollcat]

The definition is pretty arbitrary. It's more interesting, what can we learn by studying that object. Even the trivia, like tidal locking, it was one of my 10000 moments (https://xkcd.com/1053/).

[Nimitz14]

[flagged]

[tomhow]

Please don't complain about tangential annoyances—e.g. article or website formats, name collisions, or back-button breakage. They're too common to be interesting.

https://news.ycombinator.com/newsguidelines.html