About 5,201 light-years away — a light-year is the distance light travels in a full year — a planet called KIC 9663113 b quietly orbits its star. Scientists spotted it in 2015, and ever since, it has stood out as one of the worlds worth thinking carefully about. Here is why.
Where in the Galaxy Is KIC 9663113 b?
At 5,201 light-years from Earth, KIC 9663113 b is very far away. To put that in perspective, our whole solar system is only a tiny dot compared to that distance. Even our fastest spacecraft would take millions of years to reach it. Right now, we can only study this world by catching the faint signals it leaves in starlight.
The planet was discovered using the transit method. That means astronomers noticed the star KIC 9663113 getting slightly dimmer at regular intervals. The dimming happens because the planet passes in front of the star, blocking a small slice of its light — a little like a fly crossing in front of a lamp. From that tiny dip in brightness, scientists can learn quite a lot.
What Kind of World Is It?
KIC 9663113 b is noticeably bigger and heavier than Earth. Its radius — that is, the distance from its center to its surface — is about 4.6 times Earth’s radius. Its mass, or the amount of matter packed into it, is about 19.2 times Earth’s mass. Those are big numbers.
A planet in this size and mass range is often called a sub-Neptune or a super-Earth, depending on how it is built inside. Scientists aren’t fully sure which category fits KIC 9663113 b best. It could be a rocky world with a thick atmosphere on top, or it could be a world with a large envelope of gas, more like a small version of Neptune. Without more detailed measurements, it is hard to say for certain.
What we do know is that a planet this much larger than Earth would feel very different if you could stand on it. The gravity would likely be much stronger than what we feel here. But whether it has a solid surface at all is still an open question.
Scientists estimate its likely temperature is around 264 K, which works out to about -9 degrees Celsius. That is cold — similar to a winter day in northern Canada. But this number is an estimate of its average temperature under certain assumptions. The real surface or atmospheric conditions, if either exists, could be quite different.
The Star at the Center of Everything
Every planet’s story is tied closely to its star. KIC 9663113 b orbits a star called KIC 9663113. The star’s surface temperature is about 6,065 K — K stands for Kelvin, a temperature scale scientists use. For comparison, our Sun has a surface temperature of around 5,778 K. So KIC 9663113 is slightly warmer than our Sun, though not dramatically so.
Stars with temperatures in this range are often called G-type stars or sometimes yellow-white stars. Our own Sun is a G-type star, which is part of why astronomers pay extra attention to planets orbiting stars like this one. The energy coming from KIC 9663113 is probably somewhat similar in quality to sunlight, even if the exact amount reaching KIC 9663113 b is different.
There are at least two planets known in this system. KIC 9663113 b is one of them. Scientists haven’t published full details on the second planet that would let us describe it here. Multi-planet systems are interesting because they hint at how the system formed and whether stable orbits are possible over long periods of time.
The Habitable Zone — and Where KIC 9663113 b Sits in It
The habitable zone is the range of distances from 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. Liquid water is important to scientists because every form of life on Earth depends on it. We don’t know of any life that survives without it.
Importantly, being in the habitable zone does not mean a planet has water. It just means conditions might be right for water to stay liquid, if it is there in the first place. Many other things matter too — like whether a planet has an atmosphere, what that atmosphere is made of, and whether the planet is geologically stable.
Based on its estimated temperature of around 264 K and its orbit, KIC 9663113 b appears to sit in or near the habitable zone of its star. Scientists think the conditions there could, in principle, allow liquid water to exist. That is a genuinely interesting finding. But “could allow” is doing a lot of work in that sentence. We have not detected water, and we cannot confirm surface conditions from this distance. If you want to explore how habitable zones work around different types of stars, the habitable zone explorer on this site is a good place to start.
A Year That Lasts Longer Than One and a Half of Ours
One orbit of KIC 9663113 b around its star takes about 572 Earth days. That means one year on this planet is roughly one and a half times longer than a year on Earth. To cover that orbit in that amount of time, the planet must be sitting at a comfortable distance from its star — not huddled up close like Mercury, and not drifting far out into the cold like Neptune.
That longer orbit, combined with the star’s temperature, is part of why scientists calculate the planet might sit in the habitable zone. It is the combination of the star’s warmth and the planet’s distance that sets the temperature. Change either one, and the whole picture shifts.
What “Possibly Habitable” Really Means
It is easy to hear the phrase “possibly habitable” and imagine oceans and forests. The truth is much more careful than that. Scientists use the phrase to mean one specific thing: the planet is in a location where liquid water might exist, given what we know so far. It says nothing about whether life is there, or whether the planet even has a surface to put water on.
For KIC 9663113 b, we don’t yet know its atmospheric makeup, whether it is rocky or gassy, or exactly how much radiation it receives. Each of those unknowns matters enormously for habitability. Future telescopes may give us better tools for probing distant atmospheres, but KIC 9663113 b, at over 5,000 light-years away, is very challenging to study in detail with current technology. You can see how it compares to other candidates on our most Earth-like worlds list.
Still, it earns its place in the conversation. A planet about the right temperature, orbiting a Sun-like star, in a system with at least one companion — that is a combination worth keeping an eye on as our tools improve.