What is the weirdest moon in the solar system?

 I’m gonna go with Saturn's moon Iapetus.

(In Greek mythology, Iapetus is a Titan, a son of Uranus and Gaia, and the father of several well-known figures, including Atlas and Prometheus)

Take a look first

You're seeing this, right? That weird ring of mountain range around the Moon?

So here's what we know about this peculiar ring:

Its average height is 20 KM (about 12 miles), making it the third tallest mountain range in our solar system.

It circles the entirety of the Moon.

And it does so exactly around its equator.

And we haven't the faintest clue as to why.

There are hypotheses: Maybe Iapetus, just like Saturn, the planet it is orbiting, had rings. These rings may have gradually been grown to the moon and eventually crashed, forming the range.

Another suggests that iapetus turned around its axis in extremely high speeds, causing it to warm up and then for some reason slowed down, perhaps abruptly and as it was cooling off it's two halves sort of melted into each other creating this bulge.

Volcanic activity is probably not the answer because Iapetus has a very low density, only slightly greater than that of water ice. This indicates that it's composed predominantly of water ice with only a small fraction of rocky material (around 20%), so this pretty much takes volcanic activity off the list.

So what we can say with certainty is that we haven't got a clue.

But it's a heck of a question.

These photos by the way were taken in 2007 by the cassini probe.

Weird enough, right?

Wrong. It gets weirder. Let's zoom out.

This isn't shade or an area not facing the sun while the photo was taken - Iapetus is spllit into two drastically different hemispheres.

One hemisphere of Iapetus is extremely dark, almost as dark as coal, with a reddish-brown tint. The other hemisphere is remarkably bright, covered in ice, almost as reflective as Europa (one of Jupiter's moons).

The transition between these two very different terrains is quite sharp and distinct, resembling a "yin-yang" or the stitching on a baseball.

Scientists believe the dark material is accumulated dust and debris, primarily from another distant Saturnian moon, Phoebe. Iapetus is tidally locked to Saturn, meaning one side always leads in its orbit, effectively "sweeping up" this dark material like bugs on a car's windshield.

Why? Is that dust the explanation? 🤷 Don’t know.

What we do know is that the dark material absorbs more sunlight and heats up. This causes any ice in the dark regions to vaporize away, leaving behind even darker, carbon-rich residues. The vaporized ice then re-deposits in colder, brighter regions (like the poles or the trailing hemisphere), making those areas even brighter. This process, called thermal segregation, intensifies the already existing color contrast.

Well, a mountain range on the equator and two tones. strange enough!

Nope.

It keeps getting stranger.

Look again:

Iapetus has a weird shape.

It’s oblate Spheroid, but… it's not supposed to be.

Iapetus is oblate spheroid, meaning it's flattened at the poles and bulges at the equator, which is common for rotating bodies (like Earth, which bulges slightly at its equator due to its spin).

So that would work with a moon that would have been spinning much faster in its early history, with a rotation period of only about 16 hours.

But Iapetus is currently tidally locked with Saturn, rotating once every 79 Earth days…

This means Iapetus somehow froze its shape when it was spinning rapidly and then later slowed down its rotation drastically, but its rigid crust retained its original, faster-spinning form. How it slowed down so quickly, given its distance from Saturn, is a subject of debate.

To explain, Iapetus orbits much farther from Saturn than the other major inner moons (like Titan, Rhea, Dione, Tethys, Enceladus, Mimas) and this didn't happen to them.

Well, at least the Orbit is not weird! …is it?

Of course it is.

Most of Saturn's moons orbit pretty much around its equator.

But not Iapetus (of course). Iapetus has a 15 degree inclination, that means sometimes it’e moving up above the equatoral orbit, and sometimes down below it.

Because why not?

The combination of its two-tone surface, the inexplicable equatorial ridge, its "fossil" shape indicating a past rapid spin, and its unusual orbit truly makes Iapetus one of the most mysterious and captivating objects in the solar system. Scientists are still actively researching and debating the origins of these bizarre features.

Iapetus isn't just the weirdest moons in our solar system, in my humble opinion. It's probably one of the weirdest places in our solar system, period.

I think it's awesome.

Why don't Mars and the Moon have mountains?

 How can you have a vague interest in the solar system and planets (enough to post a question on Quora about them) and not have heard of Olympus Mons?!

Meet Olympus Mons (Mount Olympus) on Mars, at 22 km high, the largest mountain and volcano in the solar system:

It’s a volcano the size of France:

2 1/2 times as high as Mount Everest:

The Moon also has mountains (these are hills but hey, what a cool photo):

The highest mountains on the Moon are over 10 km high, making them significantly taller than any on Earth (Selenian summit shown in green):

Selenian summit is 10,786 m as measured from the Lunar mean surface (the Moon’s equivalent of sea level based on its average radius of 1,734.4 km). This is higher than Mauna Kea as measured from base to peak (10,210 m), and much higher than Everest (8,848 m), so it’s safe to say the Moon and Mars have bigger mountains than Earth.

Even if they’re formed by impactors and volcanoes, rather than plate tectonics.

Is there still something interesting we need to know about the Moon?

 

It is not that we know everything about the moon, not everyone will know the following things-

1- At the equator of the Moon, the temperature becomes 260 degrees Celsius during the day and minus 280 degrees at night and all this happens within 90 minutes.

2-The largest known crater in the solar system is on the south pole of the moon which is 5400 km wide. Its name is Aitken Crater which was formed by the collision of a comet 4 billion years ago. There may be valuable materials here.

3- There are very high mountains on the moon. Neil Armstrong was afraid that his spacecraft might collide with the mountains and get destroyed.

4- Alan Shepard hit a golf ball on the surface of the moon which went 800 meters away.

5- Mons Huygens is the highest mountain on the moon which is 5.5 km high. More than half the height of Mount Everest.

6- There is a place on the south pole of the moon where the temperature is colder than Pluto. The coldest place in the solar system is about -240 degrees

7- A tunnel or cave has been found on the moon which was made of lava billions of years ago and it is 500 meters wide and 50 km long. The temperature of this lava tube is -20 degrees Celsius.

8- If there was no moon, our Earth would have strayed from its orbit.

9- When Neil Armstrong reached the moon's orbit, he got goosebumps seeing the dense darkness there.

10- The moon is a vast, desolate and deserted area.

11- According to NASA, there is nothing left to explore on the moon, so they are not going to the moon. While some people say that the aliens living there have threatened NASA not to come there again.

12- It is said that some civilization had reached the Moon before humans; the remains of their aircraft are lying there.

13- Hillary Clinton had promised during the election that if she becomes the President, she will reveal some secrets about the moon and aliens to everyone but she lost the election.

The Moon is slowly drifting away from Earth

 Believe it or not, the Moon is slowly drifting away from Earth—about 3.8 cm (1.5 inches) every year! It might seem tiny, but over millions of years, this gradual shift is rewriting Earth’s cosmic story.

🔄 What’s Going On?

🌊 The Moon’s gravity pulls on Earth’s oceans, creating tides.

🌀 Those tides push back, nudging the Moon farther out.

⏳ As a result, Earth’s spin slows down—our days are getting longer!

🚀 What’s Ahead?

🌑 One day, total solar eclipses will be a thing of the past—the Moon will be too far to fully block the Sun.

🌊 Tides will weaken, transforming ocean patterns.

🔒 Eventually, Earth and the Moon may lock into a mutual orbit, always showing the same face to one another.

The Moon isn’t just orbiting us—it’s slowly waving goodbye. 🌌🌙✨

What would happen if there was no Moon?

 

"The moon is a loyal companion. It never leaves. It’s always there, watching, steadfast, knowing us in our light and dark moments, changing forever just as we do. Every day it’s a different version of itself. Sometimes weak and wan, sometimes strong and full of light. The moon understands what it means to be human. Uncomplicated, it doesn’t torment itself with guilt or sadness, only shines." - Tyler Kent White

A lot of things will happen if there is no moon. Some of these consequences will be greatly felt on Earth.

1. A. Tides would be much weaker or nonexistent, causing major changes to ocean currents, weather patterns, and coastlines.
2. B. The Earth's axial tilt, which causes the seasons, would be much less stable, leading to greater climate variability.
3. C. The moon helps regulate Earth's rotation, and its absence could cause the planet's day-night cycle to become irregular.
4. D. The Moon has a significant impact on the Earth's gravitational field, and its removal would alter the distribution of mass within the Earth-Sun system.
5. E. The absence of the moon could result in a significant increase in the number of asteroids and comets colliding with Earth.
6. F. The moon helps protect the earth from solar wind, which is a stream of charged particles from the sun. Without the moon, the earth would be exposed to more of this wind, leading to a loss of its protective magnetic field.
7. G. The absence of the moon would likely cause the earth's rotation to slow down over time, eventually leading to longer days and a slower axial rotation.
8. H. The Moon is believed to have formed from debris left over after a Mars-sized object collided with the Earth. Without the Moon, this event may never have happened, and the evolution of life on Earth could have been very different.
9. I. The Moon has a significant impact on the stability of Earth's orbit, and its absence could cause the planet to experience more extreme variations in its axial tilt and orbital eccentricity.
10. J. The moon's gravitational pull helps stabilise the Earth's axis, and its absence could result in more frequent and severe earthquakes and volcanic eruptions.
11. K. The absence of the moon could cause the earth to have a more elliptical orbit, leading to greater temperature fluctuations and changes in the length of the year.
12. L. The Moon has a significant impact on the formation and evolution of life on Earth. Its absence could have prevented the evolution of many species, including humans.
13. M. The moon is thought to have played a role in the formation of the earth's atmosphere, and its absence could have prevented the development of an oxygen-rich atmosphere.
14. N. The absence of the moon could result in a weaker magnetic field, which would make it easier for solar wind to strip away the earth's atmosphere.
15. O. The moon's gravitational pull helps stabilise the earth's orbit and prevent it from moving too far away from the sun. Without the moon, the Earth's orbit could become more unstable, leading to changes in the planet's climate.
16. P. The moon has a significant impact on the Earth's ocean currents, and its absence could result in changes to the distribution of heat and nutrients in the oceans.
17. Q. The absence of the moon could make it harder for life on Earth to adapt to changing environmental conditions, as the stability of the planet's climate would be affected.
18. R. The moon has a significant impact on the Earth's crust, and its absence could result in changes to the planet's tectonic activity and the formation of mountains and oceans.
19. S. The absence of the moon could cause the earth's axis to become more tilted, leading to greater variation in the length of the day-night cycle and changes in the planet's climate.
20. T. The moon's gravitational pull helps regulate the Earth's orbit, and its absence could result in changes to the planet's climate and the distribution of water on its surface.
21. U. The absence of the moon could prevent the formation of tides, which are important for the survival of many species of marine life.
22. V. The moon helps to regulate the earth's axial tilt, and its absence could result in changes to the planet's climate and the distribution of seasons.
23. W. The absence of the moon could affect the timing of migration patterns for many species, as well as the timing of reproductive cycles and other biological processes.
24. X. The moon has a significant impact on the earth's magnetic field, and its absence could result in a weaker magnetic field and increased exposure to harmful solar radiation.
25. Y. The absence of the moon could affect the distribution of water on the earth's surface, as its gravitational pull helps to move ocean currents and distribute heat.
26. Z. The moon has had a significant impact on human culture and history, as its regular cycles have been used for thousands of years for calendars and for navigation. Without the Moon, many aspects of human civilization could have developed differently.

STRANGE STRUCTURE IDENTIFIED “INSIDE” THE MOON

 

The Moon has one of the largest visible craters in the entire Solar System: the South Pole-Aitken basin, with a diameter of about 2,500 kilometers, present on the hidden face of the Moon. That is, the hemisphere perpetually opposite to the Earth, south of the equator. Its area has always been at the center of many investigations, and lately some scientists have identified a strange anomaly inside it, probably linked to the cause that created the crater. It is, in fact, of meteoric origin, and the body that caused its formation could still be there: in 2019, some researchers from Baylor University identified a structure with a mass of 2.18 trillion (one billion billion) kilograms and that extends for more than 300 kilometers in depth right under the large crater. The structure could be compared to a huge mass of metal, five times larger than the Big Island of Hawaii and was discovered during NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission. This observation could be used to study the internal composition of the Moon, especially considering that the asteroid that hit our satellite is dated 4 billion years old.

Source: Discovery may contain metal from asteroid crash, Baylor University researcher says, Baylor University

What is special about Callisto?

 

Callisto, the moon of Jupiter, is quite special. It is on par in size with the smallest planet, Mercury, and its characteristics and position in the orbit of Jupiter make it one of the best locations in the Solar System for a human base.

Callisto is the third largest moon in our system and the second biggest in orbit of Jupiter after Ganymede. It is also in the most distant orbit out of the four big moons of this enormous gas giant planet. This is far enough to be outside of the harmful effects of Jupiter’s magnetic field, which makes Europa and its fascinating subsurface ocean less accessible to us due to radiation. However, it turns out that Callisto might also have subsurface salty waters, but they are between 100 to 250 km/66 to 155 miles below the ground and might be 150 to 200 km/100 to 133 miles deep.

Salt-loving extremophile microorganisms or halophiles are the most likely type of life that could inhabit such an environment. Obviously, for now, this is just speculative; we have no evidence that life exists there. The ocean on Callisto is only heated by radioactivity and, unlike Europa’s, not by tidal effects, which would help mix water with the rock and provide nutrients for organisms. This is why it is less likely that we will find life there than on Europa or some other moons of gas giant planets.

Being a third bigger than our Moon, Callisto is the most cratered celestial object in the Solar System; its surface is ancient and shows no evidence of volcanism or geological activity. Since about half of Callisto is water and half rock, its cratered surface has, in places, glittery, white frost deposits. This is another feature necessary for the future human base; we could use the local water. Furthermore, the molecular composition of easily accessible material on the surface might make it possible to manufacture rocket fuel.

Its location near Europa makes Callisto additionally attractive for future human presence. This is why there is a great interest to know more about this intriguing moon; it will be visited by the European Space Agency’s Jupiter Icy Moon Explorer (JUICE), which will perform flybys between 2031 and 2034, NASA Clipper Mission flybys in 2030, and Chinese Tianwen-4 will enter the orbit of Callisto around 2030.

The question was: What is special about Callisto?

The size comparison between the Earth, the Moon, and Callisto.

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