About 290 light-years away, a large world called TOI-1736 c travels slowly around a star that looks a little like our own Sun. Scientists spotted it in 2023, and it sits in an interesting part of its solar system. But does that mean it could ever support life? The answer is more complicated than it might first seem.
Meet TOI-1736 c and Its Star
TOI-1736 c orbits a star called TOI-1736. A star’s surface temperature tells us a lot about what kind of star it is. Our Sun has a surface temperature of about 5,778 K (K stands for Kelvin, a unit scientists use to measure very high and very low temperatures). TOI-1736’s surface temperature is 5,636 K, which is just a little cooler than our Sun. That makes it a fairly Sun-like star, which is one reason this system gets attention.
TOI-1736 c is not alone. So far, scientists know of two planets in this system. TOI-1736 c is the outer of the two. It takes 571 Earth days — about one and a half years — to complete one full trip around its star. That longer orbit means it sits farther out than the inner planet, which matters a lot when we talk about temperature and liquid water.
What the Goldilocks Zone Actually Means
You may have heard the term “Goldilocks Zone” before. Scientists call it the habitable zone — the band of distances around a star where conditions might allow liquid water to exist on a planet’s surface. Not too hot, not too cold. Just right, like the porridge in the old fairy tale.
It is important to say clearly what the habitable zone is not. It is not a guarantee of life. It is not even a guarantee of water. It simply marks the region where liquid water could exist, if a planet has the right kind of surface and atmosphere. An atmosphere — the layer of gases surrounding a planet — acts like a blanket. It can trap heat and push temperatures up, or it can be too thin to make much difference. Without knowing what a planet’s atmosphere is like, we can only say that the zone is a hopeful starting point.
You can explore how the habitable zone changes depending on a star’s size and brightness with our habitable zone explorer.
Where TOI-1736 c Sits in That Zone
The estimated temperature of TOI-1736 c is about 249 K, which works out to roughly -24 degrees Celsius. That is quite cold — below the freezing point of water. Scientists calculate this kind of temperature by looking at how much light the star gives off and how far the planet orbits from it. The result is called an equilibrium temperature, meaning the temperature the planet would be if it had no atmosphere at all.
At -24 C with no atmosphere, liquid water on the surface seems unlikely. However, a thick atmosphere could trap enough heat to warm things up. We see this effect on Earth, where greenhouse gases — gases that hold in heat — keep our planet warmer than it would otherwise be. Whether TOI-1736 c has such an atmosphere is something scientists haven’t been able to measure yet.
The planet’s long orbit of 571 days places it in a region where a Sun-like star’s warmth is relatively gentle. Scientists think this orbit likely puts TOI-1736 c near the outer edge of, or just beyond, the habitable zone of its star — though pinning this down precisely depends on measurements we don’t yet have. In other words, it is in an interesting neighbourhood, but whether the conditions inside are right is still an open question.
A World Very Different from Earth
Here is where things get sobering. Even if TOI-1736 c falls in or near the right zone, the planet itself looks nothing like Earth. Its radius — the distance from its centre to its surface — is about 12.5 times Earth’s radius. Its mass is around 2,800 times Earth’s mass. Those are enormous numbers.
A planet this large and this massive is almost certainly not a rocky world like Earth. Scientists think it is far more likely to be a gas giant — a planet made mostly of hydrogen, helium, and other gases, similar to Jupiter or Saturn in our own solar system. Gas giants don’t have a solid surface for liquid water to pool on. If there is water somewhere inside or in the clouds of such a world, it would exist under crushing pressure and in forms very different from the water in a glass or an ocean.
Life as we know it needs liquid water on a stable surface. A gas giant makes that extremely difficult to imagine. That doesn’t mean such worlds are completely uninteresting to scientists — large planets can have moons, and moons can sometimes have very different conditions. But as far as we know, no moons have been confirmed around TOI-1736 c, and measuring small moons at 290 light-years is far beyond what our telescopes can do right now.
If you want to see how TOI-1736 c compares to worlds that look more like Earth, take a look at our most Earth-like worlds list.
How Scientists Found It
TOI-1736 c was discovered in 2023 using a technique called the radial velocity method. When a planet orbits a star, its gravity gives the star a tiny tug. That tug makes the star wobble very slightly back and forth. Scientists can detect this wobble by measuring tiny changes in the colour of the star’s light. A star moving toward us looks very slightly bluer; moving away, it looks very slightly redder. By tracking these shifts carefully, scientists can work out that a planet is there, how long its orbit is, and roughly how massive it is.
The radial velocity method is especially good at finding massive planets, because bigger planets create bigger wobbles. That is partly why a planet as large as TOI-1736 c was detectable at all.
What We Still Don’t Know
There is a great deal that scientists haven’t measured yet. The planet’s atmosphere — if it has one — is unknown. Its exact position relative to the habitable zone depends on details about the star that haven’t been fully pinned down. No one has measured the planet’s density in a way that tells us its precise composition. And the question of moons is completely open.
Science works step by step. TOI-1736 c is a newly found world, and every new measurement brings a clearer picture. For now, the honest answer to the question in the title is: TOI-1736 c sits in an interesting region of its solar system, but its enormous size makes it a very unlikely home for life as we understand it. Interesting? Certainly. Goldilocks-friendly? Probably not — though the universe has surprised us before, and patient observation may yet tell us something new.