Is our solar system large enough to contain all the stars in our galaxy?

 It's not as far-fetched a question as it seems, if we understand that our solar system is practically empty space.

It is estimated that the solar system would be filled with the volume of approximately 279 billion suns, and that the Milky Way has about 100 billion stars. If all stars were the size of the sun, the galaxy would not be large enough to fill the volume of the solar system.

The image shows the scale of distances between the Sun and just the first three planets. The note above states that the scale of distances is correct, but that the planets have been exaggerated by a factor of 50 and the Sun by twice their actual sizes.

However, the Sun is an average-sized star, and there are much larger stars.

This is the Sun compared to the planets.

And this is the Sun compared to some of the largest stars in our galaxy (The Sun is the smallest star in the picture).

Here compared to UY Scuti.

UY Scuti placed at the center of our solar system would reach beyond the orbit of Jupiter.

It's worth considering, then, how many stars of that size would be needed to fill the entire volume of the solar system.

I dare say the solar system would be too small, but not by much.

Why is Pluto's orbit so different from that of the other planets in the solar system?

 Pluto orbits the Sun in an ellipse and completes its revolution in about 247.9 Earth years, so it has not yet completed a complete orbit since it was discovered.

It is located at a distance from the Sun that varies between 7.37 billion km at aphelion and 4.43 billion km at perihelion.

This last value is curious because it shows how at a certain period of its year, Pluto is closer to the Sun than Neptune, which has an average distance from the Sun of 4.5 billion km, nothing similar occurs among the other planets in the Solar System.

Its orbit has two more characteristics that differentiate it from those of the other planets: it has a marked eccentricity, almost 15 times that of the Earth, and is inclined by 17 degrees with respect to the plane of the ecliptic.

This is because Pluto's orbit is influenced by Neptune and also because this is how the solar system formed it.

In fact, the solar system formed through an accretion disk, concentrated in various points, which then merged and formed the planets.

The chunk of rocky material that formed Pluto may have collided with another chunk of rocky material and thus acquired a slightly chaotic orbit, which became increasingly chaotic over time!

What would an alien civilization see if it observed our solar system?

 If an alien civilization were to observe our solar system, it would first notice a solitary and ordinary yellow dwarf star.

This is what it looks like from three light-years away, from the edge of the Oort cloud. I believe it's an artist's rendering, since none of our space probes have reached this distance yet.

It's not a very interesting view. Let's move on to the next point.

If we zoom in a little further, our alien astronomers would observe four gas and ice giants orbiting an ordinary star. Wow, one of them has a glowing ring. Amazing!

It wouldn't be that exciting anyway; planets with rings are common in this galaxy. Some even have more spectacular rings.

In any case, it's encouraging to have four large planets with such wide orbits. These planets can collect hazardous objects from space and provide some protection to the planets closer to the star. The planet beyond the ringed one is also the largest of the four. Just look at that enormous gravitational pull!

I wonder if there are planets with narrower orbits. There should be, since the other planets have fairly long orbits around the star and leave a lot of space available near the center of the system. It's not possible to observe them at this resolution. Perhaps if we were able to zoom in a little more, we should be able to see more detail.

There they are. Three… Wait… Four rocky planets in the vicinity of… Hold on a minute!

See that? One of those planets has large amounts of liquid water and oxygen on its surface. Ozone too. It looks habitable. It's the third one if we count from the star, right?

Get your drones ready, it's Goldilocks Zone! Let's explore…

If Jupiter suddenly obtained enough mass to become a star, what would happen to our solar system and would life on Earth be wiped out?

 If Jupiter suddenly gained enough mass to ignite into a star, its heat wouldn't kill us. Instead, its immense new gravity would fling millions of deadly asteroids directly at Earth.

Jupiter is composed of hydrogen and helium, the same elements that fuel our Sun. To actually become a star—specifically, a low-mass red dwarf—the gas giant would need to acquire roughly 80 times its current mass. This influx of material would generate enough internal pressure to ignite sustained nuclear fusion.

If 79 extra Jupiter masses suddenly materialized 5.2 astronomical units away, the new star's radiation would be an afterthought. A red dwarf at that distance would shine in Earth's sky hundreds of times brighter than the full moon, casting distinct shadows and glowing a deep crimson. It would provide, however, less than one percent of the heat Earth receives from the Sun. Earth's global temperatures would barely register the new heat source.

The true catastrophe would be orbital. The sudden introduction of roughly 0.075 solar masses at Jupiter's location would instantly convert the solar system into a binary star system. Earth and the other inner planets would be caught in a gravitational tug-of-war. The immediate gravitational shockwave would tear through the asteroid belt situated between Mars and Jupiter. As those millions of displaced rocks plunged through the inner solar system, the resulting bombardment would extinguish any surface life long before other climate disasters took hold.

Over a slightly longer timescale, Earth's orbit would warp into an extreme ellipse or destabilize entirely. Depending on exactly where the planets were when Jupiter gained its mass, Earth might be pulled too close to the Sun, boiling the oceans. Conversely, it could be slung outward, wandering the freezing depths of space as a rogue planet long after the asteroid strikes had leveled its surface.

A size comparison of Earth, Jupiter, a low-mass star, and the Sun. To ignite hydrogen fusion and become a star, Jupiter would need roughly 80 times its current mass. Photo by Planetkid32 is licensed under CC BY-SA 4.0.

If we could travel beyond our solar system, what could we see beyond it?

 Punch through our solar system's protective bubble, and your first encounter wouldn't be another star. The void is a wasteland of billions of unseen, freezing planets wandering the dark alone.

The space between stars is filled with the interstellar medium—a diffuse, cold mixture of hydrogen, helium, and cosmic dust. Drifting in this darkness are these rogue planets. Violently ejected from their home solar systems during chaotic early formations, they are unbound to any star and remain frozen in perpetual night. They are practically invisible, detectable only when their gravity briefly magnifies the light of a background star.

The closest stellar stop would be the Alpha Centauri system, located 4.37 light-years away. Rather than a single sun, a traveler would find a triple star system. The two main stars, Alpha Centauri A and B, orbit each other closely, bathing their surrounding space in the glare of two suns. The third, Proxima Centauri, is a small red dwarf swinging in a wide orbit. Orbiting Proxima is at least one Earth-sized exoplanet, Proxima b. On its surface, the red dwarf would loom large in the sky, casting a permanent, crimson twilight over the landscape.

Further into the galaxy, the dark void gives way to stellar nurseries. These are massive clouds of gas and dust spanning light-years across. Under their own gravity, pockets of gas collapse and ignite into newborn stars. The intense ultraviolet radiation from these young stars sculpts the surrounding dust into towering, jagged formations, such as the famous Pillars of Creation.

The Pillars of Creation as captured in near-infrared light by the James Webb Space Telescope, revealing clouds of interstellar gas and dust where new stars are forming. Source: Wikimedia Commons.

Deeper exploration would reveal the violent ends of stellar lifecycles. A traveler might encounter a pulsar—the crushed, spinning core of a dead star, firing twin beams of radiation across space like a lighthouse. If a ship traveled thousands of light-years to the center of the Milky Way, it would reach Sagittarius A*, a supermassive black hole. There, extreme gravity bends light itself, warping the visual field into a distorted ring of glowing gas and stretched background stars.

Where is liquid found in the solar system?

 

To the few places in the solar system like Earth or Titan, the moon of Saturn, where we know liquids exist on the surface, we can now add Pluto. We found evidence of liquid nitrogen flowing on its surface.

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Pluto is very frigid at -232 degrees Celsius. This is below the temperature at which nitrogen can stay liquid, especially since Pluto’s atmosphere is tenuous with very low pressure. However, the interior is probably warmer, and pressure at the base of solid-state nitrogen glaciers provides some heat.

The iconic heart-shaped feature on Pluto is called Sputnik Planitia and is composed of such glaciers. The New Horizons mission was launched in 2006, and it took 9 years to perform the first-ever human flyby of Pluto. In 2015, it sent us invaluable images and data.

Upon recent reexamination, researchers found evidence of liquid nitrogen flowing at the base of glaciers on Sputnik Planitia in the recent past. Pluto now joins the few places in the solar system with evidence of liquid on the surface.

Earth has water oceans; Titan, the moon of Saturn, has seas and lakes of hydrocarbons; there are similar water streaks on Mars as on Pluto; there are geysers on Enceladus, the moon of Saturn, and Triton, the moon of Neptune; and there are lava flows on Io, the moon of Jupiter. Additionally, many moons of gas and ice giant planets and planetoids like Ceres in the solar system have subsurface oceans or pockets of brine

Is gold older than the solar system?

 If you're wearing a gold ring, you're wearing the shrapnel of dead stars. Every atom of gold on Earth is older than the Solar System itself.

The Earth, the Sun, and all the planets in our cosmic neighborhood formed about 4.6 billion years ago from a vast, swirling cloud of gas and dust known as the solar nebula. But that nebula did not manufacture heavy elements; it simply gathered what was already drifting through space.

To understand why gold predates our solar system, it helps to look at how the universe creates elements. The Big Bang produced mostly hydrogen and helium. The intense heat and pressure inside the cores of ordinary stars can fuse these lighter elements into heavier ones, stopping at iron. The formation of elements heavier than iron—like gold, platinum, and uranium—requires an environment far more violent and energy-dense than a standard stellar core.

These precious metals are forged through a mechanism called the rapid neutron-capture process. This occurs during the universe's most catastrophic events: the explosive death of a massive star in a supernova, or the collision of two incredibly dense neutron stars. During a neutron star merger, the influx of free neutrons allows atomic nuclei to rapidly bulk up before they can undergo radioactive decay, synthesizing vast quantities of heavy elements in a matter of seconds.

An artist's impression of two dense neutron stars merging and exploding as a kilonova. This event creates the extreme conditions required to forge heavy elements like gold. Photo by University of Warwick and Mark Garlick is licensed under CC BY 4.0.

The gold forged in these ancient cosmic collisions was violently expelled into the interstellar medium, drifting through the galaxy for millions or billions of years. Eventually, this debris mixed with the hydrogen and helium of the solar nebula. When the nebula collapsed to form our solar system, the gold was already there—a relic of catastrophic collisions that took place billions of years before the Sun even ignited.

How and why doesn't our solar system attract with a black hole, as we know we have millions of them in one galaxy?

 The Milky Way contains up to a billion black holes, but they aren't cosmic vacuums. If the Sun were replaced by one of equal mass, Earth's orbit wouldn't shift a single millimeter.

A black hole does not possess extra gravity just because it is a black hole. Its gravitational pull behaves exactly like the gravity of any other object in the universe with the same mass, provided the object remains outside the event horizon.

If a black hole took the Sun's place, the planet would freeze, but it would continue on its exact current path. Black holes only consume matter that crosses the event horizon. They do not pull distant objects out of stable orbits.

Having millions of black holes wandering the galaxy sounds like a minefield until you account for cosmic scale. The Milky Way is about 100,000 light-years across and contains between 100 billion and 400 billion stars. Even at the high estimate of one billion black holes, they account for less than 1% of the massive objects in the galaxy.

The solar system is not sitting still. The Sun, the Earth, and all those millions of black holes are moving together, orbiting the center of the galaxy in a relatively stable pattern. Because everything swirls in the same general direction, and because space is mostly empty, objects rarely cross paths.

The closest known black hole to Earth is Gaia BH1, which sits about 1,560 light-years away. If the entire solar system out to Pluto were scaled down to the size of a US quarter, Gaia BH1 would still be hundreds of miles away.

A virtual reality simulation of a supermassive black hole and its glowing accretion disk. Photo by European Southern Observatory (ESO) is licensed under CC BY 4.0.

Have there always been 9 planets in our solar system or did more exist at one time ?

We just found stronger evidence for yet another planet. It was a super-Earth that fell into the Sun when the solar system was young.

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This is in addition to the Neptune-sized planet that was between Saturn and Uranus and was ejected.

Planets initially form in the protoplanetary disk from gas and dust, but as they grow larger, more and more massive rocks and eventually planetoids collide to contribute to their mass. This process ended for Earth when the Mars-sized planet Theia collided with it, forming the Moon.

There might also have been a huge world the size of Neptune between the orbits of Saturn and Uranus, and it was ejected. Some earlier studies linked this event to the Late Heavy Bombardment around 3.8 billion years ago. In this model, ejecting this planet disrupted asteroids and comets, which rained down on the remaining worlds, including Earth. However, more recent research suggests the ejection may have happened earlier and may not have been linked to the Late Heavy Bombardment.

This month, computer simulations suggest that the Sun swallowing a super-Earth planet within less than 50 million years after the solar system formed could explain some known anomalies of our star.

The lost planet might have been between 5 and 10 times as massive as Earth, and it enriched the Sun with heavy elements just below the present-day convection zone. This explains its helioseismicity, unusually low lithium abundance, and convection-zone depth. Computer simulations that tried to explain these issues by enriching the Sun with just dust couldn’t reproduce what is observed. Only swallowing a super-Earth planet agrees with these characteristics of our Sun.

Furthermore, we already know that close to 5000 systems with exoplanets and super-Earths are frequent in close orbits to their stars. The existence of a swallowed planet then confirms that our system isn’t unusual; it simply lost such a world early in its history.

How is the solar system traveling? Want to know the details?

 Hurtling at 514,000 mph, the solar system bobs up and down through the galaxy like a carousel horse. The last time Earth was in this exact spot, dinosaurs had just begun to evolve.

The Sun and its planets are in a massive orbit around the supermassive black hole at the center of the Milky Way, located about 26,000 light-years away. It takes roughly 225 to 250 million years to complete one full revolution.

The solar system does not travel completely flat along the galactic disk. The plane in which the planets orbit the Sun is tilted at a 60-degree angle relative to the plane of the Milky Way. As the Sun circles the galactic center, it crosses the midplane every 30 million years or so, oscillating vertically in a path that resembles a wave.

Currently, the overall direction of the Sun's trajectory—known as the solar apex—points roughly toward the star Vega in the constellation of Lyra. As the Sun moves toward this apex, it drags the planets along with it while plowing through the interstellar medium.

This forward motion creates a dynamic interaction with the space around it. The solar wind, a constant stream of charged particles emitted by the Sun, blows outward and forms a protective magnetic bubble called the heliosphere. When this outward pressure meets the gas and dust of interstellar space, it creates a bow wave ahead of the solar system, similar to the water parting at the front of a moving ship. This boundary shields the planets from a significant portion of high-energy cosmic rays as the entire system makes its quarter-billion-year journey around the galaxy.

A scientific illustration of the heliosphere, the magnetic bubble created by the solar wind that shields the solar system as it moves through interstellar space. Source: Wikimedia Commons.

How does our solar system orbit the Milky Way, and why does it take 250 million years to complete one orbit?

 The solar system orbits the Milky Way galaxy at an average speed of about 828,000 kilometers per hour (515,000 miles per hour), taking approximately 230 million years to complete one full orbit around the galaxy's center. This journey is often referred to as a "galactic year."

If you could teleport instantly thousands of light years outside our galaxy and look down upon it with supertelescoping vision you might see something like this:

The Milky Way galaxy spins like water going down a drain with our local group in one arm halfway between the core and the outside edge at a distance of around 27,000 light years.

Our solar system orbits with the Sun dragging the other planets in tow, making the solar system look like it is flying sideways, always moving up since the solar system is tilted that way.

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.