Are the moons of Jupiter old planets?

The large moons of Jupiter formed together with this planet as moons. In our solar system, aside from some smaller moons of the gas and ice giant worlds, Neptune has one larger moon, Triton (shown above), which did not form in this way but is a captured trans-Neptunian dwarf planet.

The story of how this happened is also extraordinary, and it might involve a huge ice giant planet that our solar system lost. It resided between Saturn and Uranus and was similar in size to Neptune and Uranus. It existed in our system for hundreds of millions of years, during which orbital resonances built up, causing the orbits of the large planets to become unstable.

This large world was ejected, causing Uranus and Neptune to move outward. Triton was at the time a transneptunian dwarf planet similar to Pluto, and when Neptune approached, it was captured into its orbit as a new moon. It now orbits it in the opposite direction from other moons, and it’s in a slow death spiral with its fate sealed. It will fall into Neptune in about 3.5 billion years.

The expulsion of this planet additionally explains the late heavy bombardment with asteroids between 4.1 and 3.8 billion years ago, which Earth and other planets and moons experienced.

Meanwhile, the lost planet became a rogue world floating in interstellar space without a star, and we will never find it. Not only did we lose it more than 4 billion years ago, but our system also moved about 16,000 light-years from where it might have formed. The Sun’s elemental makeup indicates that it might have been born in a Wolf-Rayet nebula or a nebula enriched by radiation from the Wolf-Rayet stars.

They are rare in the flat spiral disk of the Milky Way, where we are located 26,000 light-years away from the center, but common in the central bulge, which has a radius of about 10,000 light-years, and our solar system might have been born nearer to it.

Most stars form with siblings in stellar nurseries, and the Sun, being more massive than average stars, is more likely to have been born with a companion as well, but its binary system broke apart, and the sister star of our Sun is also forever lost, like the planet that was expelled. It’s probably drifting somewhere on the other side of the Milky Way galaxy, more than 100,000 light-years across, and we are unlikely to ever find it and the lost planet.

How populated is the asteroid belt between Jupiter and Mars?

 Nowhere CLOSE to what the media has prepared us for…

• FACT: The total mass of all of the rocks in the asteroid belt is just 3% of the mass of our Moon.
• FACT: The average distance between two decent sized asteroids is a few million kilometers - the distance between Earth and Moon is a third of a million kilometers.

FICTION:

Not this:

…or this..

…or this:

…or this:

SORRY. BACK TO FACTS:

The reality is more like:

…only with fewer dots!

If you were slap bang in the middle of the asteroid belt, the largest and brightest things you’d see would be the Sun and Jupiter. The odds of you being able to see a single asteroid with naked eye would be almost zero.

Flying through the asteroid belt is no big deal.

ALTHOUGH:

Science has nothing much to say either way about these:

Why do some star systems have Jupiters that are super close to their suns, and why is our solar system different?

 

The funny thing is that our Solar System may in fact be quite average. The problem lies in being able to detect exoplanets at all. The larger and closer a planet is to a star the more likely we are to detect either the wobble of the parent star or change in brightness from the transiting planet. In both cases, being close to the star makes it more likely to be detected since the orbital period is short. It also helps if the planet is large and massive such as gas giants which are really the only ones that can affect a detectable wobble. The larger surface area of gas giants also makes the change in brightness caused by a transit large enough to be detected. Our Sun’s planets, in contrast, would be hard to detect. Jupiter’s period is about 12 years which means it would take that long to see a wooble cause by it and be able cancel out the Sun’s proper motion. It is also how long you would need to wait (assuming the observer’s line of sight aligns with our ecliptic plane) for anyone to notice a repeat of the begining or end of Jupiter’s transit. Saturn would be even worse for detecting a transit since its period is 29 yrs. A Uranus or Neptune transit may be seen only once in a lifetime if at all within either period of 84 yrs and 165 yrs. Smaller planets, because of their proximity to the Sun like Mercury, Venus, Earth, and Mars would transit more often but would be harder to detect. So, it should not be surprising that the vast mayority of the exoplanets detected are Jupiter size.

There is a size comparison of all the planets to the Sun (notice the four large gas giants) in the simulated image below:

There is still a large gap between Mars and Jupiter. Could there be a possibility that a new planet will be discovered there?

 No. First of all there’s already something there called the “Asteroid belt”:

Secondly there’s not enough material there to form a planet.

And lastly if there was something there we’d have discovered it by now. That is after all how we located Neptune.

There’s planets we can see with the naked eye namely Mercury, Venus, Earth as we’re standing on it, Mars, Jupiter, Saturn and Uranus. Uranus is a special case as it’s only visible when at opposition. In other words when we’re at the closest point in our orbit to it and it’s on the same side of the Sun as us. This only occurs once a year. But we “discovered” it in the 18th century and can see it with telescopes.

But as they looked at it they noticed that it wasn’t exactly in the right spot. It was slightly off. We had learned from Newton that gravity affects other objects so that must mean something big was farther away. They did the calculations, worked out it’s location and about 70 years later we discovered Neptune.

Mars and Jupiter are much closer. If there was a planet out there we’d have seen it by now. And if not we’d have detected it through it’s gravity affecting either Mars or some of the asteroids in the belt.

So no. There’s no planet out there between Mars and Jupiter.

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.

What are the most interesting facts about Jupiter?

 Jupiter: The Solar System’s Big Boss & Its Cosmic Secrets

Source from NASA website

1. Size & Gravity: “Jupiter’s Got That Main Character Energy”

• Mass Flex: Jupiter’s 318x heavier than Earth (NASA, 2021). Its gravity game is SO strong, it either slingshots asteroids away from us or eats them like cosmic snacks.
• Earth’s Bouncer: Acts like a VIP bodyguard—blocking killer comets (RIP ShoemakerLevy 9 in 1994) but sometimes yeets space rocks toward us. Oops? 😅

2. Moons of Jupiter: “Alien Life? Maybe Chillen’ Here”

• Europa: Hides an ocean under its icy shell with 2x Earth’s water. If aliens exist, they’re probably vibing near hydrothermal vents (Science, 2017).

Europa Clipper Explores an Icy Ocean World (Artist's Concept)

• Ganymede: The only moon with a magnetic field. Basically, it’s got drip and maybe salty oceans.

Enhanced Ganymede (Enhanced Image)

Funny Thought: “Europa’s fish (if they exist) need therapy—living under 15km of ice is stressful.” 🐟

3. Great Red Spot: “The Ultimate NeverEnding Storm”

Sizing Up Jupiter's Great Red Spot (Illustration)

• Vibes: This storm is bigger than Earth (1.3x!) and has been raging since the 1600s. Scientists study it to understand Earth’s wild weather.
• Hilarious Fact: “If this storm hit Earth, you could fly from LA to NYC and still be stuck in the vortex!” ✈️🌀

4. Magnetic Field: “Jupiter’s Invisible Superpower”

Jupiter's Magnetic Field

• Strength: 20,000x Earth’s! Its radiation belts are so deadly, they’d fry your phone in seconds.
• Io’s Drama: Jupiter’s pull on moon Io creates epic volcanoes—like a sulfurspewing TikTok trend gone wrong.

5. Atmosphere: “A Time Capsule from the Early Solar System”

Jupiter is dominated by hydrogen and helium, methane, ammonia, water vapour etc. Methane, famously "fart gas".In some ways, examining Jupiter's composition gives definitive information about beginnings for the solar system.

It assists scientists in studying planet formation and inventory distribution in our corner of the Cosmos.

“Jupiter’s breath probably stinks, but hey, it’s preserving the universe’s ancient recipe!” 🌌

6. Space Tech: “Jupiter Missions = Engineering Flex”

• Juno Mission
  [1]
  : NASA’s incredible probe braved Jupiter’s intense radiation environment—often called a “radiation hell”—to uncover surprising details about the planet, including its unexpectedly “fluffy” core. This groundbreaking discovery wouldn’t have been possible without cutting-edge radiation-proof technology. Truly a triumph of engineering and science!

NASA's Juno Mission Captures Swirls in Jovian Storms

• Europa Clipper (2024)
  [2]
  : Set to explore Jupiter’s icy moon Europa, this upcoming mission will rely on state-of-the-art equipment designed to endure radiation levels a staggering 1 million times higher than what would be lethal for humans.

Europa Clipper Gets Its High-Gain On

How could Jupiter be shielding us from space debris when it is revolving in a huge orbit?

 Jupiter not only shields the earth from space debris, it also ensures that the asteroid belt does not fling asteroids into the sun or form an accretion disc and develop into a new planet. This is accomplished due to Jupiter’s mass and extraordinary gravitational effects. Space debris that could pose a danger to our planet may come in three forms. Man-made debris such as left over rocket stages, and a group of asteroids known as Hildas and Trojans.

Every planet has a gravitational pull on space debris. Any celestial body with substantial mass has an area in space between itself and another massive body known as a Lagrangian point, L-point, where the gravitational pull of both bodies settles to an average and anything stuck in this area, known as a Trojan hereon, is locked into orbit. Trojans share an orbit with planets but follow an oscillating movement along the orbit, called libration. 6 of the 8 planets in our system, including earth, have Trojans in their L-points. Earth and Venus have one each while Mars has seven. Jupiter has more than 6000 documented Trojans.

This represents data collected between 2005–2017 on the movement of both Trojans (Green) and Hildas (purple). The effects of Jupiter’s gravitational pull is evident.

Jupiter’s Trojans are classified into The Greek camp and The Trojan camp, in the leading and trailing edge of Jupiter’s orbit respectively. Jupiter’s gravitational pull is 2.5 times that of earth, and it essentially shepherds asteroids along its orbit. Hildas observe an elliptical orbit which slows their movement near aphelion. This causes them to congregate near Jupiter's L-point and create the appearance of a triangular orbit.

Jupiter is doing us a solid, no doubt, but its not our last line of defense. Not by a long shot. In case anything escapes Jupiter’s gravitational pull and heads straight for earth, our moon will be waiting.

In 1969, object J002E3, third stage of the Apollo 12 Saturn V rocket, was improperly injected into a heliocentric orbit and instead went into an unstable high earth orbit that switches between heliocentric and geocentric orbits in a 40 year cycle. It was spotted in 2003. In its approach to Earth, it was noted just how essential a part the moon plays in protecting us from debris as well.

5-year Update, April 2023:

Thanks to all the upvotes, questions, contributions and suggestions to this topic. I’m glad its peaking interest. I have updated some more info regarding the Asteroids, specifically the Hildian asteroids explaining their orbit.

Why does the storm on Jupiter never dissipate?

 

The storm on Jupiter that you are referring to is called the Great Red Spot. It is a huge, persistent, high-pressure region that produces an anticyclonic storm. It is so big that it could swallow Earth whole. It has been observed since at least 1665, which makes it one of the oldest and most enduring storms in the solar system.

Why does this storm never dissipates?

Jupiter is a gas giant planet that has no solid surface. This means that there is nothing to stop or slow down the winds that power the storm. The storm is essentially a giant vortex of swirling clouds that is driven by the temperature difference between the warm interior and the cold upper atmosphere of Jupiter.

Jupiter rotates very fast, completing one revolution in about 10 hours. This creates a powerful Coriolis force that deflects the winds and makes them spin faster. The Coriolis force also prevents the storm from moving much from its position near the equator.

Jupiter has a very complex and dynamic weather system that involves multiple jet streams, belts and zones of different colors and temperatures. The Great Red Spot is located in a region where two jet streams flow in opposite directions, creating a shear zone that stabilizes the storm and prevents it from merging with other storms.

Jupiter has a very strong magnetic field that generates intense auroras and interacts with the solar wind. This may also affect the atmospheric circulation and chemistry of the planet, and possibly influence the color and composition of the Great Red Spot.

The storm on Jupiter is a very unique and fascinating phenomenon that has been puzzling scientists for centuries. It is not likely to dissipate anytime soon, unless something drastic changes in Jupiter's environment or internal structure. It is one of the wonders of our solar system that we can admire from afar.

Why doesn't Jupiter hit the Trojan asteroid belt during revolution?

 

You might think that Jupiter, being the biggest planet in the solar system, would just smash through anything in its way. But that's not how gravity works, my friend.

Gravity is a force that pulls objects together, but it also keeps them in balance.

That's why the Earth doesn't crash into the Sun, or the Moon into the Earth. They all orbit around a common center of mass, which is slightly offset from the Sun.

Now, Jupiter has a lot of mass, so it has a lot of gravity. But it also has a lot of neighbors: the Sun, Saturn, and thousands of asteroids.

Some of them asteroids are called Jupiter trojans, because they share Jupiter's orbit around the Sun.

They are not just random rocks floating around; they are actually trapped in special places called Lagrange points.

Lagrange points are positions in space where the gravitational forces of two large bodies (like the Sun and Jupiter) cancel out.

There are five such points for each pair of bodies, but only two of them are stable: L4 and L5.

These points form an equilateral triangle with the Sun and Jupiter, 60 degrees ahead and behind Jupiter in its orbit.

The trojan asteroids are clustered around these points, like loyal soldiers following their leader into battle.

They are not fixed in place; they oscillate around the Lagrange points in complex patterns called tadpole and horseshoe orbits.

But they never stray too far from their positions, because if they do, they will feel the tug of Jupiter's gravity and be pulled back into line.

So why doesn't Jupiter hit the trojan asteroids?

Because they are in a delicate balance with the Sun and Jupiter's gravity.

They are not orbiting Jupiter; they are orbiting the Sun with Jupiter. They are not in Jupiter's way; they are in harmony with Jupiter.

How did ancient Indians calculate Jupiter's orbital period so accurately?

 Ancient Indian astronomers combined their observational and mathematical skills, and knowledge of celestial mechanics, to accurately calculate Jupiter's orbital period. They have made some remarkable contributions to astronomy,

They relied on meticulous naked-eye observations of celestial bodies, such as Jupiter, and tracked the planet's position relative to the fixed stars in the background, over long periods. They used simple instruments like gnomons (vertical sticks) and armillary spheres to measure angles and positions of celestial objects. (An armillary sphere is a model of the objects in the sky, consisting of a spherical framework of rings, centered on Earth or the Sun, that represent lines of celestial longitude and latitude and the ecliptic.)

Hindu planispheric astrolabe in brass, single plate, made for Raja Ramasimha by Sivalala in 1870. Engraved in Sanskrit with instrument laid out for the latitude of Bundi (25º 28'), Rajasthan, India. Science Museum.

The ancient Indian astronomical texts, known as Siddhantas, provided systematic methods for calculating the positions and motions of the visible planets. The Surya Siddhanta, one of the most famous texts, contains detailed descriptions of planetary motions and methods for calculating their positions. . The Surya Siddhanta includes tables of sine values. Yes, Indian astronomers developed and used trigonometric functions, such as sine and cosine, to perform precise calculations.

By observing Jupiter's position relative to the background stars, ancient Indian astronomers determined its orbital period. They noted that Jupiter takes 12 years to complete one full orbit around the Sun.