Thousands of planets orbit stars far beyond our own sun. We can’t see most of them directly — they are too small and too faint next to their blazing host stars. So astronomers had to get clever. The story of TOI-2453 b shows exactly how that cleverness works.
A Tiny Shadow Across a Distant Star
TOI-2453 b sits 267 light-years from Earth. A light-year is the distance light travels in one year — about 9.5 trillion kilometres. That is far too distant for any telescope to take a clear photo of the planet itself. The star it orbits, TOI-2453, would look like a faint dot of light even in a powerful telescope. So how do we know the planet is there at all?
The answer is shadow. When a planet passes in front of its star, it blocks a tiny slice of that star’s light. From Earth, the star looks very slightly dimmer for a short time. That small dip in brightness is the clue astronomers needed. This is called the transit method, and it is the technique that revealed TOI-2453 b in 2026.
How the Transit Method Works, Step by Step
The transit method sounds simple, but making it work takes careful planning and very sensitive equipment. Here is how it goes.
- Watch the star. A space telescope stares at a patch of sky and measures the brightness of thousands of stars at once, many times each night.
- Look for a dip. When a planet crosses in front of its star — this crossing is called a transit — the star’s brightness dips by a small amount. For a planet the size of TOI-2453 b, the dip might be less than one percent of the star’s total light.
- Wait for it to repeat. One dip on its own could be caused by many things — a passing dust cloud, a glitch in the equipment, or even another star nearby. But if the dip happens again and again on a regular schedule, that is strong evidence for an orbiting planet.
- Measure the depth and timing. How much the light dips tells scientists roughly how big the planet is compared to its star. How often the dips repeat tells them how long the planet takes to complete one orbit — its year.
The transit method is powerful, but it has a limit. It only works if the planet’s orbit happens to line up with our line of sight. If the planet orbits above or below the star from our viewpoint, we never see a transit at all. Scientists estimate that most planets are probably never discovered this way, simply because of geometry.
If you’d like to see how this process looks in action, you can explore our interactive planet-finding simulator and try catching transits yourself.
The Wobble Method — A Second Set of Ears
The transit method is not the only tool astronomers use. Another important technique is called the radial velocity method, sometimes nicknamed the wobble method.
Here is the key idea. A planet does not just orbit its star — the star also moves a tiny bit in response to the planet’s gravity. Gravity is the pulling force between any two objects with mass. The planet pulls on the star, and the star pulls on the planet. Both of them move. The star’s movement is very small compared to the planet’s, but it is real.
As the star wobbles toward us and then away from us, the light it sends our way shifts slightly. When the star moves toward us, its light gets compressed into slightly shorter waves — we say it is blueshifted. When the star moves away, its light stretches into slightly longer waves — that is called a redshift. This stretching and compressing of light waves is called the Doppler effect, and it is the same reason a passing ambulance’s siren sounds higher-pitched as it comes toward you and lower as it leaves.
By measuring these tiny shifts in a star’s light very precisely, astronomers can figure out how heavy the planet is. The heavier the planet, the bigger the wobble, and the bigger the shift in the star’s light. The radial velocity method gave scientists a way to measure the mass of TOI-2453 b — something the transit method alone cannot do.
What We Know About TOI-2453 b
Put the two methods together and the picture of TOI-2453 b becomes much clearer. The planet has a radius — that is, its distance from its centre to its surface — of about 3.24 times Earth’s radius. Its mass is about 10.6 times Earth’s mass. That combination puts TOI-2453 b in a category scientists sometimes call a sub-Neptune: bigger than Earth, but smaller than the ice giant Neptune in our own solar system.
The host star, TOI-2453, is cooler and smaller than our sun. Its surface temperature is about 3,720 K (kelvin — a scale scientists use to measure temperature, where 0 K is the coldest anything can ever get). Our own sun’s surface runs at around 5,778 K, so TOI-2453 is noticeably cooler. Stars this cool often appear orange or red rather than the yellow-white of our sun. They are called red dwarf stars, and they are the most common type of star in the Milky Way.
A Hot and Hurrying World
TOI-2453 b moves very fast. It completes one full orbit around its star in just 4.44 Earth days. For comparison, Earth takes 365 days to orbit our sun. That short year means TOI-2453 b sits extremely close to its star.
Being so close has a consequence: heat. Scientists estimate the planet’s temperature at about 551 K, which is around 278 degrees Celsius. That is far too hot for liquid water as we know it. Water boils at 100 degrees Celsius at normal air pressure, so the surface of this world — if it even has a solid surface — would be far beyond that.
What We Still Don’t Know
Even with radius, mass, and temperature in hand, many questions about TOI-2453 b remain open. Scientists haven’t measured what its atmosphere is made of, or whether it has one at all. We don’t know if it has a solid rocky surface, a deep ocean of high-pressure liquid, or a thick envelope of gas closer to a small gas planet. These are details that future telescope observations might begin to answer.
So far, TOI-2453 b is the only known planet in this system, but that doesn’t mean it’s alone. Many star systems have multiple planets, and some may simply be too small or too far from the star to have shown up yet. For now, TOI-2453 b is a fascinating example of what patient, careful observation can find — a world 267 light-years away, revealed by nothing more than a tiny, repeating dip in starlight.