In 2025, astronomers added a new world to our growing list of known planets beyond our solar system. That world is TOI-7166 b, and it sits about 116 light-years from Earth — far away by human standards, yet close enough that scientists are already asking careful questions about it.
A World Found by Starlight
TOI-7166 b was discovered using the transit method. That means scientists watched its host star and noticed the star’s light dimmed slightly, over and over, at regular intervals. A planet passing in front of the star causes this tiny dip in brightness, the way a bug walking across a lamp shade dims the light a little. Each dip tells scientists how big the planet is and how long its orbit takes.
The telescope that spotted this signal watches huge patches of sky for exactly these small changes. When a dip repeats on a steady schedule, scientists can be fairly confident a planet is the cause. That is how TOI-7166 b came to our attention.
At 116 light-years away, a light-year being the distance light travels in one full year, TOI-7166 b is not a neighbor in cosmic terms. But in the galaxy as a whole, it is in our own small corner of the Milky Way. We cannot visit it, but we can study it from here.
A Small, Cool Red Star
Every planet’s story starts with its star. TOI-7166 is what astronomers call a red dwarf — a star that is smaller, dimmer, and cooler than our Sun. We know this because its surface temperature is measured at 3,099 K (kelvin is a unit scientists use for very high or very low temperatures; 3,099 K is roughly 2,826 degrees Celsius). Our own Sun burns at about 5,778 K, so TOI-7166 is quite a bit cooler.
Red dwarfs are the most common type of star in the Milky Way. Because they shine so gently, the zone around them where conditions might allow liquid water sits much closer to the star than it does around a Sun-like star. That closeness has consequences, which we will come to shortly.
Red dwarfs also tend to live for an extremely long time — much longer than stars like our Sun. In theory, a planet orbiting one has a very long window of time in which life could develop, if conditions were right. Scientists think about this when they consider which stars are worth studying closely.
Size, Mass, and What Might Lie Inside
TOI-7166 b has a radius of 2.01 times Earth’s and a mass of 4.7 times Earth’s. That makes it what scientists call a super-Earth — a planet larger than Earth but almost certainly smaller and rockier than the giant gas planets like Neptune.
When scientists know both the size and the mass of a planet, they can estimate its density — how tightly packed its material is. A planet with more mass packed into a smaller space is denser, and likely made of rock and metal. A planet that is large but light is probably wrapped in thick layers of gas or water.
For TOI-7166 b, the numbers suggest it is somewhere between a rocky world and one with a thick atmosphere or deep layers of water. Scientists haven’t been able to pin down its exact composition yet. It could be a rocky super-Earth with a thin atmosphere, or it could hold significant amounts of water or gas. More observations would be needed to say for certain.
Temperature and the Habitable Zone
The habitable zone is the band of space around a star where temperatures might allow liquid water to exist on a planet’s surface. It is sometimes called the “Goldilocks zone” — not too hot, not too cold. Scientists are careful to say this only means water could exist there. It does not mean any particular planet actually has water or life.
TOI-7166 b has an estimated temperature of 249 K, which is about -24 degrees Celsius. That is below the freezing point of pure water. Based on this number alone, the planet sits near the cooler edge of, or just outside, where we might expect liquid water to easily exist at the surface.
However, temperature estimates like this are calculated assuming the planet reflects a certain amount of starlight. A thicker atmosphere could trap heat through the greenhouse effect — the same process that keeps Earth warmer than it would otherwise be. So a planet with the right kind of atmosphere might be warmer at the surface than this estimate suggests. We simply do not know yet what kind of atmosphere, if any, TOI-7166 b has.
If you want to explore how the habitable zone works around different types of stars, you can try the habitable zone explorer on this site.
A Very Short Year
One orbit of TOI-7166 b around its star takes just 12.9 Earth days. That is its year. To complete a full trip around its star in under two Earth weeks, the planet must be orbiting very close in.
Orbiting so close to a red dwarf raises an interesting concern. Stars like TOI-7166 can be active when they are young, releasing bursts of energy called flares. A planet sitting nearby could be exposed to quite a lot of this radiation. Whether TOI-7166 b has a magnetic field strong enough to protect it — the way Earth’s magnetic field shields us — is something scientists haven’t measured yet.
Close orbits around red dwarfs also raise the possibility of tidal locking, where one side of the planet always faces the star and the other side stays in permanent night. Scientists haven’t confirmed whether TOI-7166 b is tidally locked, but it is a real possibility worth considering.
What “Friendly to Life” Really Means
Being honest about what we know and don’t know is important here. TOI-7166 b is an interesting world. It is roughly Earth-sized in its own category, it orbits a long-lived star, and its temperature, while cool, is not wildly extreme. These are reasons to pay attention to it.
But so far, scientists have not measured its atmosphere, its surface, or its water content. The estimated temperature puts it at the chilly end of what might be livable. The short orbit means it gets a lot of stellar attention. There is only one known planet in this system so far, so we cannot say much about the broader picture of this solar system.
None of this rules TOI-7166 b out. It simply means we have more to learn. If you enjoy thinking about which worlds come closest to Earth in their conditions, the most Earth-like worlds list is a good place to compare notes. TOI-7166 b reminds us that every new discovery is a question, and the careful work of answering those questions is where the real science lives.