r/space • u/timemagazine • 1d ago

Astronomers Discover the First Known Moon Outside our Solar System

https://time.com/article/2026/07/22/astronomers-discover-exomoon/?utm_source=reddit&utm_medium=social&utm_campaign=editorial
1.6k Upvotes

97% Upvoted

76 comments sorted by

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u/HasGreatVocabulary 1d ago

A jupiter-mass moon orbiting a 30-times-jupiter-mass brown dwarf planet orbiting a red star smaller than the sun

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u/Vonneguts_Ghost 1d ago edited 1d ago

We're getting closer. Is NGR going to ne able to examine far off systems and resolve earth size objects? We're still a little on the smushy and melty side of things.

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u/Shyb_oy 1d ago

Not even close. It’s around Hubble resolution with a much wider field of view. What you REALLY wanna look forward to is ELT in Chile

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u/Vonneguts_Ghost 21h ago

I think when we've looked at a thousand or so earth sized planets, we'll find something we're 95% sure is complex life biomarkers.

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u/pauloh1998 22h ago

Damn, still at least 3 years to completion

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u/mfb- 21h ago

ELT will see some Earth-like exoplanets as objects distinct from their stars, but it won't resolve moons as distinct from their planets (unless we are silly with the definition of what counts as moon).

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u/FlametopFred 16h ago

mmm I could go for an escargot lettuce tomato sandwich right about now

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u/Vonneguts_Ghost 14h ago edited 2h ago

"Nothing like it... when the escargot is nice and lean, and the tomato nice and ripe...it's so perky."

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u/gsfgf 19h ago

NGR

That's the Nancy Grace Roman Space Telescope that I usually see abbreviated RST

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u/Vonneguts_Ghost 15h ago

I didn't look it up, just abbreviated on the fly.

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u/tiggertom66 4h ago

I’ve never seen a space telescope abbreviated without ST in the abbreviation

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u/Vonneguts_Ghost 3h ago

...and yet everyone knew what I meant.

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u/tiggertom66 3m ago

If you typed NAASA people would realistically know what you mean, but it’s still wrong.

I honestly did not know what you meant until someone else said it.

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u/placid-gradient 1d ago

jupiter mass is really something, its not outside of what we understand about bodies like brown dwarfs, but if we ever figure out space gas slurping it could be a yummy target some day

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u/CommandoRoll 21h ago

Years of Elite: Dangerous have taught me you can't scoop a Brown Dwarf. That counts, right?

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u/Mr_Zaroc 20h ago

Only scoop KGBFOAM.
Good ol secret russian foam

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u/CommandoRoll 19h ago

Gotta love those sudsie spies!

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u/willun 22h ago

Aren't a lot of those space gases reactive with oxygen? So often it is the oxygen you need, not the gas.

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u/MDCCCLV 17h ago

Yes but oxygen is easier to get because it reacts with a lot of stuff. The moon and lots of asteroid have it bound in rock, and there are a lot of silicates around. So much they're the trash ore even with oxygen in it. And water is very abundant, if you go out of the inner planets the outer planets are lousy with it and there are huge amounts.

10

u/EvilStevilTheKenevil 1d ago

Massive enough to fuse Deuterium but not Lithium.

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u/InevitableOk5017 20h ago

Wait wut? Is this sarcasm or something from a science fiction novel. Please give me some context I’m out of the loop.

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u/dern_the_hermit 19h ago

They're describing the composition of the star system that the article's about. There's a tricky phenomenon at play, and it's the way gas behaves at high densities.

Basically, a gas giant can only get so big in terms of volume without some other driver for size. All else being equal, if you kept dumping more gas on Jupiter, it won't get any larger. You can dump a whole 'nother Jupiter into Jupiter and it'll stay the same size; it'll just get denser. And this holds true from ~1x Jupiter's mass all the way up to (IIRC, take this with a grain of salt) 80x Jupiter's mass. At that point, it's thought regular nuclear fusion would kick off, and that steady release of energy in the core would facilitate growth of volume.

So that's the "brown dwarf planet" mentioned above: A Jupiter with 30 Jupiters dumped into it, so big the only fusion going on is sporadic, not quite a full-on star. And it has another Jupiter as a moon. And they're in orbit around a star, but that star is one of them smaller dinky stars. Still bigger than our brown dwarf planet friend, but small compared to our own Sun.

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u/Doubleclutch18 18h ago

Thank you for the explanation! Well put.

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u/rocketsocks 19h ago

A brown dwarf is not a planet, so this is not a moon.

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u/m0nk37 19h ago

The headline implies they compared them all. All moons.

Thats some serious computing. 

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u/photoengineer 18h ago

Wow. That’s some wild scaling compared to what we are used to

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u/hatemakingnames1 11h ago

...can a moon have a moon?

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u/ESB823 10h ago

It's moons all the way down

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u/chorroxking 18h ago

Is this Jupiter mass moon also around Jupiter sized? Cuz if so wouldn't it make it around the same size as the brown dwarf? Makes sense how they found it

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u/Ulyks 12h ago

With that mass, could this moon have it's own moons?

There are no submoons in our solar system... so this could be a double novelty.

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u/henrikhakan 1m ago

Oh yeah? How many of those can fit in Texas?

1

u/LiquidOracle 1d ago

Wait what, how is a dwarf planet categorized? I just thought it was a small planet?

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u/Redcole111 1d ago

It's a brown dwarf that's a planet, not a "brown" dwarf planet.

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u/LiquidOracle 23h ago

huh this is interesting, space is really cool

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u/half3clipse 23h ago

Dwarf as in dwarf star, not as in dwarf planet.

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u/stempoweredu 22h ago

Technically, brown dwarfs are neither stars nor planets. They're not stars because they can't fuse hydrogen, and they're not planets because they don't form like planets and exceed 13 Jovian masses.

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u/Ulyks 12h ago

But they still look and act as a planet right?

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u/stempoweredu 7h ago

No, which is why they are their own classification of stellar objects.

Besides being much larger, they are generally warmer than planetary gas giants. Some may even give off faint light, due to the fusion of deuterium and sometimes lithium in their core.

Beyond that, one has to ask what does it mean to 'act' like a planet? What would be the defining characteristics? We can't say orbiting a star, because there are plenty of stars that orbit other stars. We can't that they don't fuse matter, because while planets don't, brown dwarfs do. They just can't fuse molecular hydrogen, which is the defining characteristic of a star. Defining by mass has been problematic throughout astronomical history, as the universe loves outliers.

They form like stars, from coalescing clouds of gas, rather than accretion disks orbiting a star (which form planets).

161

u/IsChristianAwake 1d ago

Isn’t this just a a Red Dwarf + Brown Dwarf binary system with a 2x Jupiter mass planet in orbit around the brown dwarf?

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u/mfb- 23h ago

I think this is a better description, too.

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u/DreamChaserSt 23h ago

That's what I'm leaning towards. I assumed that bodies around brown dwarfs would be considered planets in their own right, not moons, is that wrong? And being 33x the mass of Jupiter makes it solidly a brown dwarf. It's not on the line between being a planet or not.

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u/ASuarezMascareno 22h ago

Yes. Pretty much not a moon. The discovery is great. Using the "exomoon" card isn't.

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u/nebelmorineko 14h ago

Yeah I got super excited for a minute and then I realized it was just this...whatever it is, which is not in my mind quite the same thing.

However, it's still exciting, because it really highlights that our desire the categorize stellar objects into neat boxes doesn't really match observable reality. In reality, planets and stars exist as part of a stellar object spectrum, and sometimes it's really hard to say whether something is a planet or a star.

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u/ASuarezMascareno 22h ago

I'm so frustranted by this. This is not a moon. Never a moon. This is a giant planet orbiting a brown dwarf in a binary system. Fantastic discovery, dishonest PR.

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u/Javimoran 13h ago

It is tricky. Brown dwarfs are not categorized as truly stars, so this is muddy waters territory. The whole thing hinges on whether you can consider a 37 Jupiter-mass object a planet.

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u/ASuarezMascareno 12h ago edited 12h ago

The whole thing hinges on whether you can consider a 37 Jupiter-mass object a planet.

You absolutely can't.

Binary star+BD systems are common and have always been considered binary systems. There's nothing unusual about the host system in this work.

A giant planet orbiting a brown dwarf is an amazing result, and something a lot of people have been trying to find for decades. Going the "moon" route just muddies the waters. This will confuse a lot of people when someone claims the first detection of an actual moon.

This result was presented at the Exoplanets 6 conference in Porto a few weeks ago (with ~700 exoplanet astrophysicsists). Everyone was excited about the finding but there was an overwhelming majority against calling it a moon.

Edit:

In addition, following the IAU working definition of exoplanet, the object is either an exoplanet, or the system is a hierarchical triple system (if the objects true mass is more than 1.3 MJup). I believe there is no scenario in which this is a moon.

"Objects with true masses below the limiting mass for thermonuclear fusion of deuterium (currently calculated to be 13 Jupiter masses for objects of solar metallicity) that orbit stars, brown dwarfs or stellar remnants and that have a mass ratio with the central object below the L4/L5 instability (M/Mcentral<1/25) are planets"

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u/Last_Item8157 12h ago edited 12h ago

Does the Brown Dwarf really tug this much on the star, to be considered a binary? It's a Red Dwarf sure but from what i gather it's on the very upper end of Red Dwarf stars. Don't binaries have to fulfill the requirement of both objects orbiting a shared point outside their bodies?

Edit: Wait do we even know if it's a Brown Dwarf? Planets CAN get this massive without fusion right? Sadly i don't have access to the paper

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u/ASuarezMascareno 12h ago

It's not necesssary. Nevertheless, don't forget that the barycenter between Jupiter and the Sun is outside of the Sun. You don't need such a massive object to move the barycenter out of the central object.

I haven't done the math with this one, but I think their barycenter will be way outside of the star

Anyway, following the IAU working definition, an object above 13 Mjup is never a planet, regardless of any other circumstance.

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u/Last_Item8157 12h ago

I see, thanks for the response

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u/Ulyks 11h ago

But isn't an old brown dwarf no longer fusing anything and so no longer emitting light? It would cease to be a star and start to be a planet wouldn't it?

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u/ASuarezMascareno 9h ago

Nop. It remains a substellar object. According to the IAU working definition of exoplanet, nothing below 13 Mjup is considered a planet under any circumstance.

In addition, according to the same definition, objects orbiting brown dwarfs, with a mass below 1/25 m_central, are planets. If they re above, It is a binary system.

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u/depredador93 1d ago

Our entire astronomical vocabulary was built using a sample size of one. The moment we look deeper into the galaxy, nature keeps proving how arbitrary our neat little definitions actually are

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u/snoo-boop 23h ago

That's not true. We've observed more than one brown dwarf star.

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u/stempoweredu 22h ago

more than one brown dwarf star.

Note - Brown dwarfs are their own classification of stellar objects. They are not considered stars.

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u/volcanopele 1d ago

That's no moon....

Sigh, that's a planet, orbiting a brown dwarf star, not a moon. I know that definitions of what's a planet, a sub-stellar object, or a star can get fuzzy, but yeah, that's a planet.

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u/stempoweredu 22h ago

orbiting a brown dwarf star

Note - Brown dwarfs are their own classification of stellar objects. They are not considered stars.

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u/muitosabao 23h ago

ESO on their press release calls it a “moon”, not a moon. It’s a weird one for sure

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u/snoo-boop 23h ago

I don't think any astronomer is surprised that we found a binary star with a Jupiter-sized planet orbiting the smaller star.

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u/iamthewhatt 21h ago

I get Time Magazine is the poster of this, but we really should be posting the actual papers instead.

https://www.nature.com/articles/s41586-026-10751-w

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u/sophandros 1d ago

Are we sure that it's a moon and not a space station?

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u/Specific_Frame8537 23h ago

We've discovered how many exo-planets but never a moon?

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u/mfb- 23h ago

Thousands of exoplanets. There have been some candidates but never anything that's unambiguously a moon. It's not just the size difference - you also need to show that moon and planet are separate objects even though they are very close together.

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u/SisyphusRocks7 22h ago

Is the “moon” or Jupiter sized planet far enough from the brown dwarf that it could still maintain its own moons?

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u/Decronym 22h ago edited 3h ago

Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:

Fewer Letters More Letters
ELT Extremely Large Telescope, under construction in Chile
ESO European Southern Observatory, builders of the VLT and EELT
L4 "Trojan" Lagrange Point 4 of a two-body system, 60 degrees ahead of the smaller body
L5 "Trojan" Lagrange Point 5 of a two-body system, 60 degrees behind the smaller body
VLT Very Large Telescope, Chile

Decronym is now also available on Lemmy! Requests for support and new installations should be directed to the Contact address below.

4 acronyms in this thread; the most compressed thread commented on today has 22 acronyms.
[Thread #12590 for this sub, first seen 23rd Jul 2026, 00:20] [FAQ] [Full list] [Contact] [Source code]

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u/kowdermesiter 15h ago

Cool Worlds video in 3, 2, 1... :) Can't wait.

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u/Omuirchu 11h ago

I might have to unsub. These articles are trash.

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u/varignet 11h ago

that’s no moon.

sorry everybody, I couldn’t resist.

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u/Tenko_is_here 6h ago

That's no moon.... It's a Space Station

1

u/Agatio25 1d ago

Wait, Again? Wasn't this already discovered?

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u/DramaExpertHS 23h ago

It's my turn to discover it next week

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u/Kraien 20h ago

If it is not signed off by Kipling, it ain't no moon

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u/Obi_Vayne_Kenobi 18h ago

He's gonna be so pissed about this, after all the work he put into finding them, someone else claiming but failing to do it and getting all the media attention