Astronomers have found thousands of planets orbiting distant stars — worlds we cannot see directly, even with the most powerful telescopes. TOI-1732 b is one of them, spotted 244 light-years away using a clever trick of light. Understanding how scientists found it is a window into one of the most creative areas of modern science.
A World 244 Light-Years Away
TOI-1732 b orbits a star called TOI-1732. A light-year is the distance light travels in one full year — about 9.5 trillion kilometres. So 244 light-years is an almost impossible distance to picture. Even our fastest spacecraft would take millions of years to get there.
The star TOI-1732 is cooler than our Sun. Its surface temperature is 4,202 K. (K stands for Kelvin, a way scientists measure temperature starting from the coldest possible point. Our Sun’s surface is around 5,778 K for comparison.) A star this cool glows with an orange-red colour and is called a K-type star — a little smaller and dimmer than the Sun, but still a steady, long-lived star.
So far, TOI-1732 b is the only planet scientists have confirmed in this system. There may be others hiding in the data, but none have been announced yet.
The Transit Method: A Tiny Shadow in the Light
The transit method is the main reason we know TOI-1732 b exists. Here is how it works, step by step.
- A telescope stares at a star and measures how bright it is, very carefully, over a long period of time.
- When a planet passes directly in front of that star — an event called a transit — it blocks a small slice of the star’s light.
- The telescope records a tiny dip in brightness. This dip lasts for a short time, then the brightness goes back to normal.
- If the same dip happens again and again, on a regular schedule, scientists know something is orbiting that star.
The dip is very small. Imagine holding a coin in front of a distant streetlight. The coin blocks only a tiny fraction of the glow you see. A planet in front of a star works the same way. The bigger the planet compared to the star, the deeper the dip. But even large planets cause only a small change — often less than one percent.
From the size of the dip, scientists can work out how big the planet is compared to its star. That is how we know TOI-1732 b has a radius — that is, the distance from its centre to its surface — of about 2.5 times Earth’s radius. It is a noticeably larger world than ours, though not a giant like Jupiter.
If you want to see how astronomers watch for these dips, our interactive simulator shows the transit method in action.
The Wobble Method: Measuring a Planet’s Pull
The transit method is brilliant, but it only gives us size. To find mass — how much matter a planet actually contains — scientists use a second technique called the radial velocity method, sometimes nicknamed the “wobble” method.
Here is the key idea: a planet does not orbit a completely still star. Both the star and the planet pull on each other through gravity. As the planet goes around, it tugs the star in a small circle too. This makes the star wobble slightly.
Scientists detect that wobble by watching how the star’s light changes colour — very slightly — as the star rocks toward us and then away. When the star moves toward Earth, its light looks a tiny bit bluer. When it moves away, it looks a tiny bit redder. This shift in colour is called the Doppler effect, and it is the same reason a siren sounds higher as an ambulance approaches and lower as it drives away.
By measuring how fast the star wobbles, scientists can estimate the planet’s mass. That is how we know TOI-1732 b has a mass of about 6.78 times Earth’s mass. That is a solid, hefty world — heavier than Earth, but far lighter than the gas giants in our solar system.
What the Numbers Tell Us About TOI-1732 b
Put radius and mass together, and scientists can calculate density — how tightly packed a planet’s material is. Density is a clue to what a planet might be made of.
TOI-1732 b is 2.5 times wider than Earth but only 6.78 times more massive. If it were made of the same rocky material as Earth, you would expect it to be heavier for its size. The fact that it is not quite as dense as a pure rock world suggests it probably has a thick atmosphere or a layer of lighter materials — perhaps water or gas — wrapped around a rocky or iron core. Scientists call worlds like this sub-Neptunes. They are a very common type of planet in the galaxy, even though we have none in our own solar system.
This is all careful interpretation, not a certain answer. Scientists are drawing reasonable conclusions from indirect measurements taken 244 light-years away. More observations could change the picture.
A Hot, Fast World: Orbit and Temperature
TOI-1732 b completes one full orbit around its star in just 4.12 Earth days. Our own year is 365 days, so this planet moves incredibly fast. It orbits very close to TOI-1732 — far closer than Mercury sits to our Sun.
That closeness comes with heat. Scientists estimate the planet’s equilibrium temperature — the average temperature of its surface or atmosphere if heat were spread evenly — at around 658 K, which is roughly 385 degrees Celsius. That is hot enough to melt lead. It is far outside the habitable zone, the region around a star where temperatures could allow liquid water to exist on a planet’s surface. TOI-1732 b is not a candidate for life as we know it.
What We Still Don’t Know
There is a long list of things scientists have not measured yet. We do not know whether TOI-1732 b has an atmosphere, or what that atmosphere might be made of. We do not know the exact composition of the planet’s interior. We do not have a precise age for the star or the planet. Future telescopes may be able to examine the planet’s atmosphere by studying how starlight filters through it during a transit — a technique called transmission spectroscopy — but that work, if it happens, lies ahead.
TOI-1732 b is a useful reminder that discovery is a beginning, not an ending. Finding a planet is the first step. Every number we have comes from careful, indirect detective work — watching light change across an enormous distance. What we know is real, and what we don’t know yet keeps the questions worth asking.