What is the size of a rogue planet?

We just measured the mass of a rogue planet for the first time, and it is similar to Saturn’s

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KMT-2024-BLG-0792 / OGLE-2024-BLG-0516 is a recent microlensing event detected by both ground and space-based telescopes that made it possible to identify and measure the mass of a rogue planet located near the outer edge of the central bulge of our galaxy. When we observe such an event across multiple instruments, we can estimate the mass of the microlensed object because of the time delay in observing the object at different locations in space and on Earth.

This extraordinary discovery indicates that rogue planets with masses below that of Jupiter exist and may be more widespread than previously believed. We already observed directly, with the James Webb Telescope, many double Jupiter-size planets in the Orion Nebula in 2023. At first, we thought they were ejected from newly formed planetary systems, but other theories of their formation have since been proposed. They might have formed via the fragmentation of nebulae in which stars form when they collide.

Nevertheless, a large population of such planets is likely to form in star systems and be ejected during the turbulent early history of those systems. Planets form via collision with planetoids and other planets within the protoplanetary disk, and a large number of them are expected to be ejected. When a large gas giant planet is banished from a protoplanetary disk, in about 90% of cases, it loses its moons, and some can become rogue planets, as well. Let’s not forget that planets more massive than Jupiter can have moons as massive as Earth and even larger.

We now think that we previously underestimated the number of transneptunian objects in our system. There could be up to 10,000, some as large as Mars and even half the mass of Earth. We can only detect them for 1% of their orbit, which can take tens of thousands of years, and our technological civilization is too young to take advantage of the short window for their possible detection until we get better instruments that could see these objects even when they are far away. They can also be ejected sometimes and become rogue planets.

This is why the upper estimate of the number of rogue planets is as large as 100,000 for each star

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 . Some can have subsurface oceans heated by the tides of a moon and by radioactivity. There is even speculation that some may have liquid water on the surface if they have a specific atmospheric composition that prevents heat from escaping. This is even though they float freely in space, without a star to provide heat, and it means that they can be a fascinating destination for the search for extraterrestrial life or stopovers in our quest to reach other star systems.

This also means that rogue planets can be any size, but we cannot see them yet if they are too small—they don’t produce their own light.

The question was: What is the size of a rogue planet?

Footnotes

[1] 

https://www.science.org/doi/10.1126/science.adv9266

[2] 

Nomads of the Galaxy

If a black hole is the size of a grain of sand, would it still be considered a black hole?

 The singularity of a black hole is absurdly smaller than a grain of sand, so yes.

The singularity is essentially the center of the black hole; it's where matter is drawn in with no possibility of escape.

The rest of what we "see" of a black hole, the accretion disk (the part that emits light), is just the event horizon. In reality, it's ridiculously far from the singularity in human terms. Especially if we're talking about supermassive black holes, where the distance is several million kilometers...

The singularity is of zero size in classical physics, or something relative to the Planck length. But the gravitational pull is so brutal that the accretion disk can be thousands of times the size of a star...

To give you an idea, in a supermassive black hole, the distance between the accretion disk and the singularity would be absurdly greater than the distance between the Earth and the core of the sun.

That's the scale we're talking about...

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.

What is the maximum size limit for objects in space?

 Well. There’s the biggest star we have seen to date:

Size comparison of a hypothetical quasi-star/black hole star (diameter of ~10 billion kilometres or ~7,187 solar diameters, mass of 1000+ solar masses) and several known giant stars: Stephenson 2-18 (~2150 solar diameters), VY Canis Majoris (~1420 solar diameters, ~17 solar masses), Betelgeuse (~887 solar diameters, ~11.6 solar masses), the Pistol Star (~306 solar diameters, ~27.5 solar masses), Rigel (~78.9 solar diameters, ~23 solar masses), and R136a1 (~35.4 solar diamaters, ~265 solar masses). Image credit: Wikimedia Commons/Sauropodomorph (CC0 1.0)

And then there’s the biggest black hole to date:

The largest black hole ever discovered. Estimates of its mass and size make this black hole a true behemoth, and it is unlike anything in our galaxy or in any of the galaxies in our galactic neighborhood. The mass of the central black hole is estimated to be 100 billion times larger than the sun. The supermassive black hole is even more massive than some galaxies, and is about 10% the mass of the entire Milky Way. The event horizon of the black hole has a diameter of 590 billion kilometres, or about 100 times the distance between the sun and Pluto. That little dot in the middle is the orbit of Neptune.

And then there’s the largest galaxy discovered to date:

Its full span is 5.5 million light-years across: nearly double the Local Group’s full extent.

Then there’s superclusters of galaxies:

Finally, there’s Quipu:

The colored dots represent different superstructures out to 800 million light-years from Earth. The red dots denote Quipu, the largest known structure in the nearby universe. Yellow is Sculptor-Pegasus superstructure, green is Serpens-Corona Borealis, purple is Hercules and blue is Shapley. Image via Böhringer et al. Astronomy and Astrophysics, 2025.

There are 185 galaxy clusters within these five superstructures. Quipu alone has 68 galaxy clusters.

What are the things that surprise you because of their size?

 1. ERShR-7000 excavator, a true titan of earthmoving technology.

2. This is the titan arum, considered one of the largest unbranched flowers in all of biology, and can grow to be 3 meters tall. However, it is not its size that draws the most attention from those who approach it, but rather its smell. The flower is known for its characteristic smell of rotting meat, capable of causing nausea even in the strongest stomachs.

3. The impressive size of these honeycombs, produced by traditional Nepalese bees.

4. This is the giant bullfrog, which can reach 32 centimeters in length and weighs about 3.25 kg. It certainly lives up to its name.

5. Meet the Holorusia mikado , the largest mosquito in the world. The specimen in the photo is 10cm long and was captured in China. Normally, mosquitoes of this species are not that big – reaching, on average, 5cm. Even so, they are quite large compared to other insects of this type. The good news about them is that sucking blood is not part of their routine.

6. Allure of the Seas, one of the largest passenger ships in the world. This giant can accommodate up to 6,400 passengers in its facilities.

7. 6-ton tires, 4 meters high, designed for Japanese special trucks.

8. This is Pamela Wang, the woman who became famous for finding the largest avocado in the world, at least that has been recorded. At 2.4 kg, it surpassed the previous holder of the record, which was 1.8 kg.

9. What you see in the photo is the largest swimming pool in the world, located in Chile, very close to the shore of the Pacific Ocean. At 1kg long, it takes 250 million liters of water to completely fill this pool.

10. The largest wine barrel, with a capacity of 205,574 liters of the drink.

11. Coco-de-mer, the largest nut ever found on the planet, weighing 25kg, measuring 1.5m in length and 0.9m in diameter. Incredible, isn't it?

12. This tree, nicknamed General Sherman, is considered the largest living being in the world, with an incredible 84m in height and 11m in diameter at the base.

13. The anchor chains of the Queen Mary 2 cruise ship are simply colossal in size. This is necessary to anchor a ship of such surreal size to the ground.

Universe Size Comparison