In 2026, astronomers confirmed a new world orbiting a star called TOI-2133, sitting about 245 light-years from Earth. That star and its planet, TOI-2133 b, are now part of a growing map of worlds beyond our solar system. Here is what we know so far, and what remains a mystery.
What Kind of Star Is TOI-2133?
TOI-2133 is what astronomers call a K-type star — a star that is cooler and smaller than our Sun. Its surface temperature is 4,250 K (kelvins, the unit scientists use to measure very high heat). Our Sun’s surface sits around 5,778 K, so TOI-2133 burns noticeably cooler and glows with a more orange tint rather than the yellow-white light we see from the Sun.
Stars like this are common in our galaxy. They live for a very long time — longer than our Sun — because they burn their fuel more slowly. That long lifespan is one reason scientists find K-type stars interesting when they search for planets. A planet around such a star has a long time to develop, whatever that might mean for it.
TOI-2133 is the only star in this system as far as we know, and so far scientists have confirmed just one planet orbiting it.
How Scientists Found TOI-2133 b
Astronomers discovered TOI-2133 b using the transit method. This is a way of spotting planets by watching for tiny dips in a star’s brightness. When a planet passes in front of its star from our point of view, it blocks a small amount of starlight. That tiny dimming is a signal that something is orbiting the star.
The transit method is one of the most successful tools we have for finding exoplanets — planets that orbit stars other than our Sun. You can explore how many worlds have been found this way on the discovery timeline.
The name TOI stands for TESS Object of Interest. TESS is a space telescope that watches large areas of the sky and flags stars where brightness dips are spotted. From those flags, astronomers then do follow-up work to confirm whether a real planet is the cause. TOI-2133 b passed that confirmation process in 2026.
Size, Mass, and What That Tells Us
TOI-2133 b is bigger than Earth, but smaller than the giant planets in our solar system. Its radius — the distance from the center to the surface — is about 2.37 times Earth’s radius. Its mass is about 6.21 times Earth’s mass.
Putting those two numbers together is useful. Scientists use radius and mass to estimate a planet’s density — how tightly packed its material is. A large but light planet might be mostly gas. A smaller but heavy planet might be made of rock or metal. TOI-2133 b sits in a range that scientists call a sub-Neptune. These are worlds bigger than Earth but smaller than Neptune, and they are among the most common types of planets we find around other stars.
Whether TOI-2133 b has a solid surface, a thick atmosphere, or some mix of both, scientists haven’t determined yet. Its density hints that it likely has some kind of gas envelope around it, but the details are still being worked out. You can compare it with other known worlds in the atlas.
A Year in Under Four Days
One of the most striking things about TOI-2133 b is how fast it orbits its star. One full orbit — what we would call a year on that planet — takes only 3.83 Earth days. That is less than four days for a complete trip around its star.
This happens because TOI-2133 b orbits very close to TOI-2133. The closer a planet is to its star, the faster it has to travel to stay in orbit, and the shorter its year becomes. Mercury, the innermost planet in our solar system, has a year of about 88 Earth days — and that already feels short. TOI-2133 b’s year is far shorter still.
A short orbit like this is common among the planets that the transit method finds most easily. When a planet passes in front of its star often, astronomers have more chances to spot the dips in brightness and confirm the discovery.
Heat and What It Means for Habitability
Because TOI-2133 b orbits so close to its star, it receives a great deal of energy. Scientists estimate its temperature at around 798 K, which is roughly 525 degrees Celsius. That is far hotter than any oven and well above the temperature at which water turns to vapor.
The habitable zone is the range of distances from a star where liquid water could exist on a planet’s surface — not too hot, not too cold. TOI-2133 b sits well inside the inner edge of that zone. As far as we know, conditions there would not support liquid water on a surface. That does not tell us everything about the planet, but it does mean scientists do not consider it a candidate for the kind of life we know on Earth.
What We Still Don’t Know
TOI-2133 b was confirmed recently, and there is still a lot to learn. Scientists haven’t measured details like the composition of any atmosphere it might have, whether it has moons, or exactly what its surface or upper layers look like. Future observations with more powerful telescopes may help fill in some of those gaps over time.
What we do have is a confirmed world — real, measurable, and 245 light-years away. Each planet like TOI-2133 b adds one more point of comparison as scientists try to understand how planets form and what kinds of worlds exist across the galaxy. That steady, careful work is what moves our knowledge forward.