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Twenty New Moons Found Orbiting Saturn (carnegiescience.edu)
205 points by japaget 62 days ago | hide | past | web | favorite | 67 comments

Here's a visualization I made of the Saturn system with an option to highlight the newly discovered moons:


Besides the 20 new moons, I find it interesting that there are 8 "lost" moons. These are objects observed as far back as 2004 - but their current locations are unknown.

That visualization is awesome! Everyone try it. You can easily zoom in and our and rotate in any of the 3 axis. It's amazing to see how far away these 'new moons' are from being in the same plane as the older, larger moons.

Is there an astro term for differentiating the planar moons and the outer ones? That moon cloud looks like as if it is Saturn's Kuiper belt or Oort cloud.

This, your other examples, and spacekit as a whole are absolutely amazing. Thanks for sharing this link.

+10 for spacekit [0]

[0] https://typpo.github.io/spacekit/

I am in heaven playing with this.

Sorry but this is the end of my comment.

I wanted to say this, but since you did already, I'm going back to playing with the moons...

Is there a reason why moons don't seem to orbit above Saturn's poles?

Conservation of angular momentum. Stars and their planetary systems form out of clouds of dust and gas which collapse into a fuzzy disk and then into bodies. The sum of the angular momentum before and after has to be the same so there is a big statistical pressure towards all bodies rotation and orbital planes to be near some average overall plane, there are gravitational forces at work too. Orbits over poles are as far off plane as possible and so are least likely.

Then why don't they orbit in the same direction, as the planets do? Aren't many moons gravitationally captured in any case?

Gravitational capture is the only way retrograde orbits could happen - a blob of spinning dust and gas just won't produce moons orbiting in opposite directions. Anything going in the "wrong" direction will be subject to a whole lot of drag forces and lose all of its orbital speed and fall inwards. Retrograde orbits have to happen by grabbing something late or after the formation phase.

All of the discovered retrograde orbiting moons are in similar orbits which suggests they all came from some larger object broken apart. Keep in mind all of these new objects are quite small, just a few miles across. About a billion of them could fit inside Saturn's largest moon, Titan (seventeen were discovered).

Regular moon fits with what I was talking about before.

Irregular moons are the ones with eccentric, retrograde, or otherwise weird orbits and acquisition histories.

The more you get into specifics about this kind of thing, the less concise and accurate you can be, it would take an expert up to date with the literature to go much deeper.

>Keep in mind all of these new objects are quite small, just a few miles across. About a billion of them could fit inside Saturn's largest moon, Titan (seventeen were discovered).

With planets, we started getting too many "planets" when we discovered more and more really tiny ones, so we started coming up with new names for them: "dwarf planet", "Trojan", "asteroid", etc. A small rock in the asteroid belt orbits the Sun, but it still isn't called a "planet".

It sounds like we need to do something similar with moons, or else it's going to get out of control. There's likely an absurd number of small rocks orbiting Saturn and Jupiter; should they really all be called "moons"?

"should they really all be called "moons"?"

Well, some of them are called "rings"...

Moons generally orbit on the same plane as their planet's orbit plane

Is this because polar orbits are unstable in some sense, or because pretty much everything already is in the planet's plane?

That's a good question, and I don't think you'll find an especially convincing answer.

Polar orbits are "unstable" in a few senses, namely that even in an ideal setting orbital planes will precess around central masses that are lumpy rather than spherically symmetric; rotation of a lumpy central mass introduces further precessions. Nodal precession is pretty interesting, for example. One can concoct all sorts of odd orbital changes by perturbing the rotating central mass "under" a test object in stable orbit.

However, in the case of known solar system bodies, slowly shifting a satellite in near-polar orbit into a near-equatorial orbit conflicts with quite a lot of evidence; by the mid 1960s it was pretty safe to say that known inner moons maintain over very long timescales an almost constant orbital inclination with respect to the planet's equator, while outer moons maintain an almost constant orbital inclination with respect to the invariable plane of the solar system. Interesting exceptions are Triton and Earth's moon, both of which have significant inclinations to their planets. Precessions are primarily driven by the planet for the inner moons, and by the sun for the outer moons.

It's probably worth paying some close attention to Uranus and its known moons (and their formation and/or capture) when considering the various thoughts people have put into the thread. Most of the moons and rings have negligible inclination (i.e., they're coplanar with Uranus's equator), and Uranus's extreme axial tilt is intriguing. If the tilt is because of a giant collision, did the relevant moons and rings follow the planetary tilt? Or did they form in the highly-tilted equatorial plane (for some of the moons), or were they captured into the equatorial plane (for others) post-tilt?

Mostly because of conservation of angular momentum: the solar system formed while spinning, and that direction has been maintained. The cases where this is not true (for example, Uranus has its poles "facing the plane" instead of having them orthogonal to it) are likely due to past collisions with foreign bodies that caused the tilt to appear.

Are most of these moons from when the solar system formed?

Maybe not, but the angular momentum is. Without a big input of energy and momentum to cause a plane change, anything that forms in the solar system will orbit roughly in the plane of the ecliptic, and will spin on an axis normal to it.

Planets sprouting new moons, flinging off old moons – reminds of the 1983 coin-op video game, 'Mad Planets':


Very cool! I'm surprised that they orbit so quickly!

The speed measurement in the viz adjusts "visualization days per real second". It's set at 0.1 because the inner moons orbit very quickly. Pan orbits Saturn every 14 hours whereas Fornjot, the outermost named satellite, orbits every 1354 days.

I couldn't find any information about the "lost" moons you mentioned. Tell me more. What is the name of one or all of those moons?

The moons are: S/2004 S 7, S/2004 S 12, S/2004 S 13, S/2004 S 17, S/2006 S 1, S/2006 S 3, S/2007 S 2, S/2007 S 3.

There are short Wikipedia articles for each one.

JPL provides orbital elements but presumably they are not quite correct, otherwise we could locate them: https://ssd.jpl.nasa.gov/?sat_elem

Very cool! It would be nice if there was a 'Highlight None' option in the drop-down.

Thanks! I've added this now.

Impressive! It looks just like celestia! I'm in awe

Fun. Is there a way to accelerate?

We had the Cassini spacecraft in the Saturn system for 10 years, and in the past two years we've found 32 new moons! We've found 67% more moons with earth-based telescopes than we discovered actually being there. Wow, space is big and we know nothing. (Of course, I don't think Cassini was actually looking for new moons on the outskirts, but still, I'm surprised we didn't accidentally find some of these...)

Cassini's instrumentation was focused on studying surfaces, not finding moons https://en.wikipedia.org/wiki/Cassini%E2%80%93Huygens#Instru...

A peeve I have would be to use a language of certainity ("has moons"):

> This brings the ringed planet’s total number of moons to 82, surpassing Jupiter, which has 79

When it's clear we don't have the absolute truth. We need to be humble. It's clear then that Saturn has at least 82 moons. Or maybe not even that, taking account the "lost" moons mentioned in this discussion. Now we believe that Saturn has about 82 moons.

This is a problem with science reporting in general. Current theories or observations are presented as absolute truth even though they're only approximations of the truth based on our current data and understanding of what's really going on.

>language of certainty ("has moons")

I don't read it that way. This is a science topic, I think the phrase "Jupiter, which has 79" does NOT mean "no more than 79" but does mean at least 79 that we know.

I don't think it signals a lack of humility. I think it is just shorthand for "Jupiter has 79 moons, that we have verified". Since this is in the context of discovering more moons that we hadn't seen before, I don't think the extra verbiage is necessary and is implied. Of course we are in the process of discovering more moons. That's what the entire article is about.

maybe they should have just said they are the 'known' moons.

Isn't the term moon devalued too much by now? Isn't there terminology to classify these newly found 5km natural satelites differently from the massive moons like ours, Ganymede, Europa and so on? Something like dwarf moons or micromoons?

Call them dwarf moons, until they have cleaned away the other moons

How about space stations?

I propose "mμns."

I wonder when these are gonna go the way of Pluto: Saturn has n moons and a shit-ton of dwarf moons. Wouldn't know where the threshold is though, because something like Phoebe is an absolute outlier.

That was my immediate thought - that the definition of ‘moon’ must have recently changed.

Currently, the only way the definition of 'moon' can change is if it gets defined at all.

It’s amazing that we still keep discovering so many new things in our own neighborhood, and as another comment notes, still hard to keep track of things as relatively close as Saturn’s “lost” moons.

This makes it kind of silly whenever we make confident assumptions about how much of X or Y must be out there in the rest of the Universe.

(Not to knock the efforts of people who did accurately predict many facts about faraway phenomena while being stuck on Earth.)

I wish they would open up the naming of at least one moon to whatever the internet decides to come up with, rather than restricting it to the same old boring gods and goddesses convention. That moon would probably become one of the more popular celestial bodies in the solar system based on that alone.

I hope you're ready for Moony McMoonface, or something less printable…

Someone out there is working really, really hard to compose a phonetic Moony McMoonface from among the available phonetic options.

“Today, class, we’re going to learn about Saturn’s newest moon, whose name the district has forbidden me from actually saying.”

Think of all the confusion that could be caused if the voted name was actually "whose name the district has forbidden me from actually saying".

Like setting your wifi password to "FOURWORDSALLLOWERCASE"

"And tomorrow, we'll be discussing Uranus."

I vote for the name being the Unicode character U+1F315.

What's wrong with gods and goddesses? Those are great names, and not subject to the idiocy that a democratic naming would come up with ("Moony McMoonFace"), which future generations would just roll their eyes at, or insist on renaming. The names of gods and goddesses are timeless.

Or we could open up to more deities outside of the roman/greek arena. How about Cthulu or Freya?

How come we are finding these new moons around Saturn just now? Did we not see them before?

Nooo, my sci-fi novels!!

  git commit -am 'Needs more moons'

Christopher Walken cowbell style Waow!

Any notion of why the Earth has only one moon and other planets have hundreds?

The earth is small and the moon relatively large (diameter 27% of that of earth; next is Triton, at 5%; volume-wise, the difference is even larger), so I guess the moon caught a lot of candidates. They may have more moons, but we likely have more moon, by mass, relatively.

And does it? https://en.wikipedia.org/wiki/Claimed_moons_of_Earth#Modern_...)

Of the four terrestrial planets, two have no moons, one has two tiny moons, and one (Earth) has a large moon. The jovian planets have lots of moons, but they are giant planets.

The question is more “why does Earth have a big moon” than “why doesn't Earth have a slew of moons like a jovian planet.”

The Earth is miniscule in comparison to the planets that have hundreds of moons. Those just have a stronger gravity field

What about Mars?

Mars has two itty-bitty moons, and the other two terrestrial planets have zero moons. Earth’s moon has something like 99.99998% of the mass of all moons of terrestrial planets.

The "moons" of Mars are really nothing more than asteroids; they're a tiny fraction of the size of our Moon, and not even large enough to be round.

It only has two moons, one more than earth for sure but nothing compared to the more massive planets.

Mars has even less mass than earth (5.972 × 10²⁴ kg vs 6.417 × 10²³ kg)

The Earth has more than one moon. There are surely a bunch of very small rocks orbiting the Earth which we haven't discovered yet. And there was one other known moon of Earth, called 2006 RH120, in the last decade, but it was ejected.



my understanding is that a good feature of the goldilocks zone is that it has fewer small objects than the outer planets region. maybe someone with better knowledge can pipe up.

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