Just 23.6 light-years away, a small, dim star called GJ 667 C holds five worlds in its orbit. That might not sound far by cosmic standards, but it is still trillions of miles from home. One of those worlds, GJ 667 C g, has caught scientists’ attention in a special way.
A Star With Five Worlds
GJ 667 C is what astronomers call a red dwarf — a star much smaller and cooler than our Sun. Its surface temperature is about 3,350 K (Kelvin is the unit scientists use for very high temperatures; 3,350 K is roughly 5,570 degrees Fahrenheit). That sounds hot, but our Sun burns at nearly 5,778 K, so GJ 667 C is noticeably cooler and gives off a reddish-orange glow.
Red dwarfs are the most common type of star in the Milky Way. They burn their fuel slowly and can last far longer than stars like our Sun. That long life means any planets around them have a huge amount of time to evolve and change.
GJ 667 C is not alone in space, either. It is part of a triple star system — three stars that are gravitationally connected to each other. The other two stars in the group are called GJ 667 A and GJ 667 B. GJ 667 C is the smallest of the three. Its five known planets all orbit this one small star.
Meet GJ 667 C g
Of the five planets in this system, GJ 667 C g is one of the most studied. Scientists measure planets in comparison to Earth because Earth is what we know best.
GJ 667 C g has a radius — that is, the distance from its center to its surface — about 1.99 times Earth’s. So it is almost exactly twice as wide as our planet. Its mass, meaning how much matter is packed inside it, is 4.6 times Earth’s. A planet in this size and mass range is sometimes called a super-Earth. That just means it is bigger and heavier than Earth but smaller than a planet like Neptune.
One year on GJ 667 C g — the time it takes to complete one full orbit around its star — lasts 256 Earth days. That is a little shorter than our year of 365 days. Because the star GJ 667 C is much dimmer than our Sun, a planet can orbit fairly close to it and still not be blasted with too much heat.
Scientists discovered GJ 667 C g in 2013, along with other planets in the system. They used a technique called the radial velocity method, which we will look at in the next section.
How Scientists Found These Planets
Finding a planet around another star is not easy. Planets don’t produce their own light. They don’t show up in a photograph the way stars do. So scientists have to be clever about how they detect them.
The radial velocity method works by watching a star’s light very carefully. When a planet orbits a star, its gravity gives the star a tiny tug. This makes the star wobble slightly — not enough to see with your eyes, but enough to measure with sensitive instruments. As the star moves toward us, its light shifts to slightly bluer wavelengths. As it moves away, the light shifts to slightly redder ones. Scientists call this the Doppler effect — it is the same reason a siren sounds higher-pitched as a car drives toward you and lower as it drives away.
By measuring these tiny shifts in the star’s light over many nights, scientists can figure out whether a planet is there, roughly how massive it is, and how long its orbit takes. This is how all five planets around GJ 667 C were found.
A Family of Five
Having five planets orbit a single star is not unusual — our own Solar System has eight. But every planetary family has its own personality, its own arrangement, and its own set of puzzles.
Around a cool, dim red dwarf like GJ 667 C, the planets tend to orbit much closer to their star than the planets in our Solar System do. This is partly because the star is so much fainter. To receive enough warmth, planets need to sit nearer. This can make the system feel more tightly packed when you compare it to the wide spacing between Mercury, Venus, Earth, and Mars.
Close orbits also mean shorter years. While GJ 667 C g takes 256 days per orbit, some planets around red dwarfs complete a full year in just days or weeks. Scientists haven’t published full measurements for all five worlds in this system, so we don’t yet have a complete picture of exactly how they are all arranged.
You can explore the layout of systems like this one in our system explorer, where astronomers’ best current data is mapped out planet by planet.
Could Any of These Worlds Support Life?
This is the question that draws many people to exoplanet research — the study of planets around other stars. Scientists think about something called the habitable zone. That is the range of distances from a star where temperatures might allow liquid water to exist on a planet’s surface. Liquid water is important because, as far as we know, all life on Earth needs it.
Because GJ 667 C is a cool star, its habitable zone sits much closer to it than Earth sits to our Sun. Some of the planets in this system may fall within that zone. But sitting in the habitable zone does not mean a planet has life, or even water. A planet also needs the right kind of atmosphere — the layer of gases surrounding it — and many other conditions we don’t fully understand yet.
Red dwarf stars can also produce powerful flares, which are sudden bursts of energy. These flares could strip away a planet’s atmosphere over time, especially if the planet orbits very close. Scientists are still working out how serious this risk is for planets like those around GJ 667 C.
As of now, we don’t know whether any planet in this system has liquid water, a breathable atmosphere, or life of any kind. What we can say is that the conditions are interesting enough to keep studying.
Why Nearby Systems Matter
At 23.6 light-years away, GJ 667 C is considered a neighbor in galactic terms. One light-year is the distance light travels in a year — about 5.9 trillion miles. So even our closest cosmic neighbors are almost impossibly far for us to visit today.
But distance matters for a different reason: the closer a star system is to Earth, the easier it is to study. Telescopes can gather more detailed light from nearby stars. Scientists can look more carefully at the planets’ sizes, masses, and orbits. Over time, future instruments may even be able to analyze the gases in these planets’ atmospheres from here on Earth.
GJ 667 C and its five worlds remind us that our galaxy is full of planetary families we are only beginning to understand. Every system we map adds a new piece to the puzzle of how planets form, how stars shape them, and whether life might find a foothold somewhere beyond our own world.