HD 27969 b is an exoplanet — a planet orbiting a star other than our Sun — sitting about 222 light-years from Earth. Scientists discovered it in 2021, and it raises a natural question: could this distant world be friendly to life? The answer, as with most exoplanets, is layered and interesting.
What Kind of World Is HD 27969 b?
HD 27969 b is a very large planet. Its radius — the distance from its center to its surface — is about 12.9 times that of Earth. Its mass is around 1,526 times Earth’s mass. Numbers like those put it firmly in the company of the giant planets in our own solar system, like Jupiter and Saturn, rather than rocky worlds like Earth or Mars.
Scientists found HD 27969 b using the radial velocity method. This technique works by watching for tiny wobbles in a star’s light. When a planet orbits a star, its gravity gently tugs the star back and forth. That motion causes small shifts in the color of the starlight that telescopes can detect. From those shifts, scientists can work out that a planet is there, and estimate its mass and orbit.
One orbit of HD 27969 b around its star takes 655 Earth days — nearly two Earth years. Its estimated temperature is around 261 K, which is about -12 degrees Celsius. That is below the freezing point of water.
Meet the Host Star, HD 27969
Every planet story starts with its star. HD 27969 is the star that HD 27969 b orbits. Its surface temperature is 5,966 K (kelvins — a scale scientists use to measure heat, where 0 K is the coldest anything can be). For comparison, our Sun’s surface is about 5,778 K. So HD 27969 runs just a little warmer than our Sun. That makes it a fairly similar star in terms of heat output, though scientists haven’t published all of its other details in the data we have here.
Stars that are similar to our Sun are interesting to researchers studying habitability — the idea of whether a world could support life. Our Sun has kept Earth warm enough for liquid water for billions of years. A star with a similar temperature could, in principle, do the same for planets in the right orbits.
So far, only one planet has been found in this system. That doesn’t mean other planets aren’t there — it may simply mean none have been detected yet. Finding planets is hard work, and smaller or more distant worlds can be easy to miss.
What Is the Habitable Zone?
The habitable zone is the range of distances from a star where conditions might allow liquid water to exist on a planet’s surface. Scientists sometimes call it the “Goldilocks zone” — not too hot, not too cold. Liquid water is important because, as far as we know, every living thing on Earth needs it. Scientists use water as a key marker when thinking about whether a world could support life.
It is very important to understand what the habitable zone is not. Being inside the habitable zone does not mean a planet has liquid water. It does not mean a planet has life. It simply means the distance from the star is right so that, under certain conditions, liquid water could exist. A planet still needs the right atmosphere, the right geology, and many other things we don’t fully understand yet. You can explore how the zone changes for different stars using our habitable zone explorer.
The habitable zone shifts depending on a star’s brightness. A hotter, brighter star has a habitable zone farther out. A cooler, dimmer star has one much closer in.
Where Does HD 27969 b Sit in the Zone?
This is the heart of the question. HD 27969 b has an estimated temperature of about 261 K, or roughly -12 degrees Celsius. That is below the freezing point of water at standard conditions. On its own, that temperature suggests the planet is on the cool side — possibly near the outer edge of, or perhaps just beyond, the habitable zone of its star.
However, a planet’s temperature as scientists estimate it is not the whole story. Temperature estimates for exoplanets are often rough calculations based on how much starlight the planet receives. They don’t account for an atmosphere. An atmosphere — the layer of gases surrounding a planet — can trap heat, much the way a blanket keeps you warm. This is called the greenhouse effect. Earth itself would be far colder without its atmosphere trapping heat.
So while the numbers suggest HD 27969 b is chilly, scientists can’t say for certain whether the planet is truly outside the habitable zone without knowing much more about it — including whether it even has a solid surface or a meaningful atmosphere at all.
Size and Mass: Why They Matter for Life
Here is where things get complicated in a useful way. HD 27969 b is enormous. With a radius nearly 13 times Earth’s and a mass over 1,500 times Earth’s, this is almost certainly not a rocky planet with a firm surface. Planets of this size tend to be what scientists call gas giants — worlds made mostly of hydrogen, helium, and other gases, without a solid ground to stand on.
Life as we know it seems to need a surface — somewhere for chemistry to happen, for water to pool, for structures to build and break. Gas giants in our own solar system, like Jupiter, are not considered good candidates for life on their own. It’s possible that large moons around a gas giant could support life, but we have no confirmed evidence of that anywhere, and we don’t know whether HD 27969 b has moons at all.
If you’re curious about worlds that look more Earth-like in size and mass, our most Earth-like worlds list looks at planets that sit closer to Earth’s proportions.
What We Still Don’t Know
The honest answer to the title question is: we don’t know enough yet to say for sure. Scientists haven’t measured HD 27969 b’s exact distance from its star, its atmospheric composition, or whether it has moons. We don’t know if its temperature estimate accounts for any greenhouse warming. We can’t see its surface — if it has one.
What we do know is that its estimated temperature is below freezing, its size matches a gas giant rather than a rocky world, and its star is fairly Sun-like. Taken together, those clues suggest HD 27969 b is probably not a strong candidate for life as we know it. But space science is full of surprises, and every new measurement of this system could shift the picture. That is part of what makes exploring the cosmos so rewarding — the universe rarely gives up its answers all at once.