TOI-5486 b is a world about four times wider than Earth, circling a dim star some distance from our own Sun. It sits in a category of planets that our own solar system completely lacks — making it one of the more interesting puzzles scientists are working on right now. Getting to know it means thinking carefully about size, mass, and what hides beneath a planet’s outer layers.
A Distant Star and a Very Fast Year
TOI-5486 b orbits a star called TOI-5486, which lies 293 light-years from Earth. A light-year is the distance light travels in one full year — about 9.5 trillion kilometres. So 293 light-years is an enormous distance, yet in cosmic terms it is a fairly close neighbour.
The star TOI-5486 has a surface temperature of 3,750 K (K stands for Kelvin, a way scientists measure temperature starting from absolute zero — the coldest anything can ever be). For comparison, our Sun’s surface sits around 5,778 K. That makes TOI-5486 noticeably cooler and dimmer than our Sun. Stars like this are called red dwarfs. They burn slowly and can live for tens of billions of years.
TOI-5486 b races around its star very quickly. One full orbit — what we would call a year on that world — takes just 2.02 Earth days. That is faster than most people’s working week. To complete an orbit so quickly, the planet must be extremely close to its star. As far as scientists know, this is the only planet confirmed in the TOI-5486 system so far.
How We Found It
TOI-5486 b was discovered in 2026 using a technique called the transit method. A transit happens when a planet passes in front of its star from our point of view. As it does, it blocks a tiny fraction of the star’s light. Telescopes detect that small dip in brightness. If the dip repeats on a regular schedule, scientists can be fairly confident a planet is orbiting there.
The transit method is powerful because it gives scientists the planet’s size right away. The deeper the dip in light, the larger the planet crossing the star’s face. By measuring how much light was blocked, researchers could work out that TOI-5486 b is about 3.97 times wider than Earth.
Getting the mass requires a separate technique — usually measuring tiny wobbles the planet causes in the star. Scientists were able to pin down the mass too, which is important because size alone only tells part of the story.
Size and Mass — Reading the Numbers
Here is where things get interesting. TOI-5486 b has a radius of 3.97 times Earth’s and a mass of 14.9 times Earth’s. Together, those two numbers let scientists calculate something called density — how tightly packed the material inside the planet is.
Think of it this way: a ball of rock and a ball of cotton candy might be the same size, but the rock is far heavier because its material is more densely packed. Density works the same way for planets. A planet that is large but not very massive must be filled with lighter stuff — gases, water, or ice. A planet that is small but very heavy must be packed with denser material, like rock or metal.
When you crunch the numbers for TOI-5486 b, the density comes out lower than you would expect for a purely rocky world. This tells scientists the planet almost certainly has a large envelope — a thick outer layer — of lighter material surrounding a denser core. That is exactly what earns it the label mini-Neptune. You can explore how size and mass relate for many planets on the mass-radius diagram, which makes these comparisons easy to see.
Inside a Mini-Neptune
No one can look directly inside TOI-5486 b. Scientists have to make educated guesses based on the planet’s size, mass, and what they know about how planets form. But those guesses can still be quite informative.
Mini-Neptunes — planets roughly two to four times the size of Earth with masses that don’t reach the level of a full Neptune — are thought to have layers. At the centre there is likely a solid core made of rock and possibly metal. Above that, there may be a thick layer of water, ice, or other compounds that behave oddly under extreme pressure. Then, wrapping everything up, there is probably a deep atmosphere of hydrogen, helium, or water vapour — or some mixture of all of these.
Scientists think that last layer, the atmosphere or envelope, is responsible for puffing mini-Neptunes out to their large sizes. Without it, TOI-5486 b might look much more like a rocky super-Earth. With it, the planet balloons to nearly four times Earth’s width. Exactly how thick that envelope is, and precisely what it contains, are questions scientists haven’t been able to answer yet for TOI-5486 b.
If you enjoy comparing planet sizes visually, the size comparison tool lets you stack TOI-5486 b next to Earth and other worlds.
A Scorching Orbit
Because TOI-5486 b orbits so close to its star and completes a lap every two days, it receives a fierce amount of radiation. Its estimated temperature is around 752 K — roughly 479 degrees Celsius. That is well above the melting point of lead. Even though TOI-5486 is a cool, dim red dwarf, sitting this close to any star means absorbing a great deal of heat.
At these temperatures, TOI-5486 b sits nowhere near what scientists call the habitable zone — the region around a star where conditions might allow liquid water to exist on a planet’s surface. The habitable zone around a red dwarf is much closer to the star than it would be around our Sun, but TOI-5486 b appears to orbit even closer than that. Any liquid water on the surface would be impossible under these conditions, as far as scientists can tell.
What We Still Don’t Know
Honest science means admitting what remains uncertain, and for TOI-5486 b there is quite a lot. The composition of its atmosphere — if it has a distinct one scientists can study — is not yet known. We don’t know whether the thick envelope is mostly gas, mostly water, or a mix. The exact structure of its interior is a careful estimate, not a confirmed fact. Scientists also haven’t detected any other planets in this system, though that doesn’t mean none exist — they may simply be too small or orbit at angles that make detection difficult.
TOI-5486 b is a good example of how much a few key measurements can reveal, and how much still stays hidden. Its size, mass, and temperature sketch an outline of a hot, layered world unlike anything in our solar system — and filling in that outline is work that future observations may slowly make possible.