Is the size of a planet or star limited by the laws of physics? Could there be a planet as large as our sun, or a star as large as our solar system?

 Yes, the laws of physics limit the radii of planets and stars (we talk about the radius here because mass is heft, while size means dimensions).

No, there could not be a planet as large as the Sun, using the standard definition of planet (that is, not calling a stellar object a planet just because it orbits another star).

No, there could not be a star as large as our solar system. The largest stars yet observed have radii which may approach that of the orbit of Saturn, around 9-10 AU; in contrast, the radius of our solar system as a whole is more like 100,000 AU.

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Such mega-massive stars sit just beneath the Eddington limit, which is the point at which outward radiation pressure exceeds inward gravitational force. Beyond this, they could not cohere as objects — this is what happens when stars go poof.

Stars like this (St2-18, say, or UY Scuti) are extremely low-density; their masses do not scale up with their sizes in the way you might intuitively suppose. If the Sun is a solid baseball, then these guys are gas-filled hot air balloons in comparison.

They’re big puffballs of radiation, shining with extreme luminosity but barely holding together gravitationally.

Models are being refined as scientists gather and analyze more data, but we think this maximum size is somewhere near 2,000 R☉. Two thousand times the radius of the Sun is intimidating enough! But poke it with a toothpick and it bursts (so to speak).

UY Scuti has nearly 2K times the girth of the Sun, but that is still nowhere near the radius of the whole solar system.

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The radius of a planet is constrained by the fact that, the more mass you add, the more gravitational compression you get scrunching the thing down smaller, or at least preventing it from expanding into something larger. (So, more mass = bigger planet only up to a point.)

Eventually, if you add enough mass, this compression will ignite fusion and you get a star instead.

Jupiter is fairly typical in radius for a really big gas giant. We have observed some which are larger — often 1.5–2 RJ, and in rare extreme cases perhaps as large as 6 RJ. But when you get that big, it’s possible you’re looking at a brown dwarf. Gas giants don’t get a whole lot bigger than Jupiter unless they’re quite hot (i.e., in close orbit of a star). Otherwise 2RJ could mean something like twenty times Jupiter’s mass, and that’s inviting deuterium fusion.

You can have rocky planets as large as a few Earth radii. But if you doubled the mass of Earth, you would only increase its radius by around 20–30%. Here again, gravitational compression is a limiting factor.

And they call gravity the weakest force! Well, it is, but it utterly dominates at the scale of everyday objects, including suns and worlds.

The True Size of the Solar System’s Largest Volcano Will Shock You.

This is Olympus Mons of Mars, the largest volcano of our solar system… Crazy Large.

Many don’t realise how big we're talking, so here is a comparison with Mount Everest and Mount Loa.

At approximately 25 km, it is three times higher than Mt Everest, which is only 8.8 km high.

Surprised? Let me tell you, this is nothing in front of its size comparison.

It’s almost the size of France with an area of 300,000 km², it's so wide that you wouldn't even know you're on a mountain.

And this large area also means that it is significantly harder to climb Everest than Olympus, mainly because it is a very gradual and wide volcano. Its average slope is only 5%.

But why does it even exist?

Except for the fact that possibly it once had lava flows 100× bigger than Earth’s, the most important reason is Mars’s gravity. Mars has only 38% of Earth’s gravity, and that allows structures to grow much taller without collapsing under their own weight.

But you know what’s the funny part, our initial understanding about this giant volcano was a “Snow-Capped Mountain”(1870s–1900s). We even named some bright patches Nix Olympica, which literally means “The Snows of Olympus”. It was mainly because of weak telescopes, and its enormous height also made it look brighter than the surroundings, which felt like snow.

And even today, the name is totally wrong; it literally came from a misidentification, which means “snow patch”… it sounds cool though.

Mariner 9 narrow angle camera of Olympus Mons' central caldera. (March 7, 1972)

This image by Mariner 9 aircraft was among the first images to confirm that Olympus Mons was a volcano.

Digital mosaic of Olympus Mons, taken by the Viking 1 Orbiter. (February 1, 2016)

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Sources: science.nasa.gov, reddit.com

And there are hundreds of more interesting facts about this discovery that we can talk about, numerous findings that have improved our understanding of things over the years that we can dive into.

Is the Earth floating, flying, or falling?

 When I was in school, I saw the solar system in a 2-dimensional plane like this:

When we look at the solar system in static 3D, we will definitely think about the existence of a hypothetical invisible field that holds the planets and the sun from falling, called ether, like the animation below:

The view of the existence of ether is actually just an illusion and will change when we include the fourth dimension, namely motion, in the solar system simulation, so it will look like this.

Of course, the solar system's helical motion isn't entirely accurate, as the planets' actual tilt around the sun is 60 degrees. So, the most realistic depiction of the solar system's motion is something like this.

It's very complicated, isn't it?

So, is the Earth floating, flying, or falling? I prefer to use the words "thrown" and "bound" by the sun's gravity, which also moves with the galaxies thrown around in this vast universe.

Perhaps someday this explosion will turn into a Big Crunch, and everything will return to its original state, only to explode again, forming a new universe. And so on, endlessly.

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:

Why is Pluto no longer considered a planet?

 The reason that Pluto is no longer a planet is not because of its size. In fact, it passes the test for "size" (mass).

The definition of 'planet' was made more strict. It is as following:

1. Massive enough to be round. Very massive bodies have so much gravity that they crush down any irregular edges towards their centre, and so become ball-like.

2. The primary object orbiting the Sun. For instance, the Moon orbit's the Sun, but it does so by orbiting the Earth. The Earth is the primary object orbiting the Sun.

3. Has cleared it's own orbit. Planets clear their orbits of debris/asteroids (by attracting them with their gravity).

Pluto passes 1 and 2, but has not passed 3. It has not cleared it's orbit of debris.

Objects like Pluto are called Dwarf Planets.

What is the reason for the Sun not being free?

 because even the Sun can’t pay the energy bill to escape the Milky Way.

It's hold in it's place because of the gravitational field of some even bigger star.

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The concept is simple but brutal. You want out? You better be fast enough. Escape velocity is the speed required to break out of a gravitational well and it’s not optional.

• For Earth to escape the Sun it requires around 42 km/s.
• For Sun to escape the Milky Way it needs around 537 km/s (depends on exact position)

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Again it's not that simple because the more massive the object you're trying to escape from, the deeper the well, and the more energy it takes.

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Let’s say you want to knock Earth out of orbit. You’d need to give it a speed boost of 12 km/s to escape Earth's gravity.
To get it out of the Sun’s orbit at least around 42 km/s is needed.

That’s a lot, but now look at Jupiter which is 318 times the Earth’s mass. You wanna knock it off its orbit you’ll need so much energy you’ll blow up your calculator.

Now apply this to the Sun and you’re talking about lifting 1.989 × 10³⁰ kg of mass out of a galactic orbit that’s been spinning for 4.6 billion years.

The energy required isn’t even insane but actually transcendental.

You would need a force greater than anything we’ve seen in the known universe like short of galactic collisions, supernova clusters, or the wrath of a rogue black hole on a bender.

Just like a rocket needs more fuel to carry more weight, breaking gravitational bonds gets exponentially harder with mass.

Like example, to knock Mercury out of orbit, It's possible with god-tier nukes.

To knock Earth out more energy is needed.

For Jupiter we need galactic-level tech.

And the Sun itself we'd need to rewrite physics, or harness energy at Type III civilization levels. (On the Kardashev scale, we haven’t even hit 0.8.)

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Sun is not a prisoner because it's weak.
It's a prisoner because gravity doesn’t care about power, it cares about proximity and mass.

And just like you can’t flinch a mountain with your bare hands, you can’t knock a star off its galactic path without rewriting the entire dance of creation.

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And the funny part is we don’t even know what gravity is 😁😂. We don’t even know how this jail works.

• Is it a curve in spacetime?
• A field?
• A hypothetical graviton particle?
• A leak from extra dimensions?

We observe gravity. We measure its effects.
But we still don’t understand what causes it at the fundamental level.

These rules are still an unsolved riddle wrapped in tensor equations and unsatisfied physicists.

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Till then Sun is just another inmate in a multilevel cosmic prison.
It burns. It rages. It illuminates life.
But it’s stuck.
Not by choice, not by failure but by the same rule i.e. the rule of gravity that traps galaxies, black holes, and photons.

Freedom, in this universe, has a price.
And the Sun can’t afford it either.

How Big is the Sun Compared to Earth?

 

Have you ever looked up at the Sun and wondered just how big it really is compared to our planet? We know it’s massive — it lights up our days, fuels life on Earth, and governs the motion of planets. But when you dive into the actual numbers, the scale becomes almost unbelievable.

Let’s Start with Diameter

Earth’s diameter: ~12,742 km

Sun’s diameter: ~1,391,000 km

That means the Sun is about 109 times wider than Earth.

Now imagine placing 109 Earths side by side… and you’d just match the width of the Sun.

Now Think in Volume

Here’s where it gets even crazier:

You can fit approximately 1.3 million Earths inside the Sun if it were hollow and you could pack the Earths in like marbles.

Let that sink in — 1,300,000 Earths!

A Visual Comparison

If we scaled it down to everyday objects:

If the Sun were a basketball, the Earth would be the size of a sesame seed.

That’s how small we are in comparison.

Why is the Sun So Huge?

The Sun is a G-type main-sequence star, mostly made up of hydrogen and helium. Its enormous size allows it to generate immense pressure and temperature in its core, where nuclear fusion takes place — the process that powers the Sun and emits the energy we see as sunlight.

A Gravitational Giant

Due to its size and mass, the Sun contains about 99.86% of the total mass of our entire solar system. That’s why all the planets — including Earth — orbit around it.

Final Thought

Understanding the size of the Sun isn’t just about numbers — it gives us perspective. We live on a small planet, orbiting a massive star, in just one corner of a vast galaxy. And yet, here we are, thinking, learning, and exploring it all.

Are there more planets than we know so far?

 Absolutely ! There are roughly 

${10}^{21}$ ( sextillion ) planets in the visible Universe, and at least 106 known exoplanets only within the surrounding sphere with 100 light years radius.

One of my favorite exo-solar system is the Trappist-1 system:

Trappist-1D:

Trappist-1C:

Proxima Centauri-B:

Furthermore !

There can be bizarre Planets such like our newborn Earth was 4.8 billion years ago:

Moreover:

L4L5 Interferometric Exoplanet Spy System (LIESS)

Basic concept:

Launching two spacecraft to the L4 and L5 points of the Earth's orbit path to study exoplanets within 100 light years.

Expected discoveries and resolutions (without claiming to be complete):

Real-time observation of the planets Proxima Centauri B and C at 13.4

meter/pixel resolution and even real-time monitoring of their meteorology.

Imaging of planets in the Trappist star system at a resolution of 134 meter

per pixel and real-time observation of their meteorology.

Costs and implementation:

The implementation, in contrast to the Proxima Centauri approach planned

for 2069, is much simpler than ion-gun acceleration technology and

would provide continuous observation of at least the surrounding

exoplanets within 100 light years, instead of a one-time journey.

… and another 106 exoplanets, if we only take the ones known so far, and possibly more exoplanets and even exomoons may emerge with a terrain map of unprecedented detail. We can boldly say that with this technology we will see the pimple on the ant's dick on the celestial bodies in the Cuiper belt and the Oort cloud, and we will get global maps comparable to the detail of Google Maps of more than 10 times as many planets as we have known so far. For example, it can easily be found that there are not just 106, but actually 268 exoplanets within the surrounding sphere of 100 light-years radius, and they have 778 exomoons. We can boldly say that with this "penny" and relatively simple tool we can find out what the word "weather" means.

Earth-Mars Orbit Configuration

1. Base Distance:
   Base distance: approximately 1.5 astronomical units (AU) = $2.25\ast {10}^{11}$ meters
2. Observation Wavelength:
   Let's assume an optical wavelength of $500nm$ ($500\ast {10}^{-9}$ meters)
3. Angular Resolution Calculation:
   The formula for angular resolution is: $\theta =\frac{\lambda }{B}$
   Where: $\theta$ is the angular resolution in radians
   $\lambda$ is the observation wavelength
   $B$ is the base distance
   
   Substituting the values: $\theta =\frac{500\ast {10}^{-9}m}{2.25\ast {10}^{11}m}\approx 2.22\ast {10}^{-18}rad$
4. Convert to Distance on Proxima Centauri B:
   Distance to Proxima Centauri B: $4.24$ light-years ($4.02\ast {10}^{16}$ meters)
   $d\cdot \theta =4.02\ast {10}^{16}m\cdot 2.22\ast {10}^{-18}rad\approx 8.92$ meters/pixel

Neptune Configuration

1. Base Distance:
   Base distance: approximately $30.1$ astronomical units (AU) = $4.5\ast {10}^{12}$ meters
2. Observation Wavelength:
   Let's assume an optical wavelength of $500nm$ ($500\ast {10}^{-}9$ meters)
3. Angular Resolution Calculation:
   The formula for angular resolution is: $\theta =\frac{\lambda }{B}$
   Where: $\theta$ is the angular resolution in radians
   $\lambda$ is the observation wavelength
   $B$ is the base distance
   
   Substituting the values: $\theta =\frac{500\ast {10}^{-9}m}{4.5\ast {10}^{12}m}\approx 1.11\ast {10}^{-19}rad$
4. Convert to Distance on Proxima Centauri B:
   Distance to Proxima Centauri B: 4.24 light-years ($4.02\ast {10}^{16}$ meters)$d\cdot \theta =4.02\ast {10}^{16}m\cdot 1.11\ast {10}^{-19}rad\approx 4.46$ meters/pixel

These calculations show the angular resolution and pixel distance for both configurations. The Neptune configuration provides a higher resolution due to the larger base distance between the observation points.

Thus, with the above-mentioned method, we will soon be able to easily observe planetary and lunar systems outside our solar system.