Teegarden’s Star d is one of three known planets orbiting a small, dim star just 12.5 light-years from Earth. That makes it one of our closer neighbors in the galaxy. Scientists announced its discovery in 2024, and it has already raised some interesting questions about what worlds near our solar system can look like.
Meet Teegarden’s Star
The host star is called Teegarden’s Star. It is a red dwarf — a type of star that is much smaller, cooler, and dimmer than our Sun. Its surface temperature is 3,034 K (Kelvin is a scale scientists use to measure temperature; 3,034 K is roughly 2,761 degrees Celsius). Our Sun, by comparison, burns at around 5,778 K, so Teegarden’s Star is noticeably cooler.
Red dwarfs are by far the most common type of star in the Milky Way. They burn their fuel slowly, which means they can shine for hundreds of billions of years — far longer than stars like our Sun. Because they are so dim, they were hard to study for a long time. Today, better instruments have helped astronomers find planets around many of them.
Teegarden’s Star is also notable because it is so close to us. At 12.5 light-years away, it sits inside what astronomers sometimes call our cosmic backyard. Only a handful of star systems are nearer to Earth than this one.
The Planet Itself
Teegarden’s Star d is remarkably similar to Earth in size and mass. Its radius — the distance from its center to its surface — is 0.95 times that of Earth. Its mass is 0.82 times Earth’s mass. In other words, it is very slightly smaller and a little lighter than our own planet.
Those numbers put it firmly in the category scientists call rocky planets — worlds that are likely made of rock and metal rather than thick clouds of gas. Earth, Mars, and Venus are all rocky planets. Planets much more massive than Earth tend to hold onto thick gas layers, more like Neptune or Jupiter. Teegarden’s Star d, based on what we know, probably does not.
Scientists haven’t measured its atmosphere, its surface features, or whether it has any moons. Many details about this world are still unknown, and it will take future observations to fill in those gaps.
A Very Short Year
One of the most striking things about Teegarden’s Star d is how fast it travels around its star. One full orbit — what we would call a year — takes just 26.1 Earth days. So a “year” on this planet is less than one Earth month.
This happens because the planet orbits very close to its star. Red dwarfs are dim and give off far less heat than our Sun, so their habitable zone — the region where conditions might allow liquid water — sits much closer in than Earth’s distance from the Sun. Planets in those tight orbits naturally move faster and complete their laps more quickly.
A short year also has other possible effects. Planets that orbit very close to their stars can get tidally locked — meaning one side always faces the star, just as one side of the Moon always faces Earth. Scientists are not yet sure whether Teegarden’s Star d is tidally locked, but it is something they consider for planets in such close orbits.
Temperature and the Question of Habitability
The estimated surface temperature of Teegarden’s Star d is 159 K, which is about -114 degrees Celsius. That is very cold — far colder than anywhere people live on Earth, and colder even than Antarctica in the heart of winter.
This places the planet outside what scientists typically consider the habitable zone of its star. The habitable zone is the range of distances where liquid water could exist on a planet’s surface, given the right conditions. At -114 °C, liquid water is not possible on a bare surface without something to warm the planet significantly.
It is worth noting, though, that surface temperature estimates for distant exoplanets — planets outside our solar system — come with real uncertainty. The figure of 159 K is a careful estimate, and factors like a planet’s atmosphere, reflectivity, and geology can all change the actual temperature at the surface. Scientists will need far more data before drawing firm conclusions. For now, Teegarden’s Star d appears to be a cold world, and there is no evidence of life or liquid water there.
How Scientists Found It
Teegarden’s Star d was discovered in 2024 using a technique called the radial velocity method. Here is how it works: as a planet orbits a star, its gravity gives the star a tiny tug. This causes the star to wobble slightly — first toward us, then away from us, then back again. When a star moves toward us, its light waves bunch together and shift toward blue. When it moves away, the waves stretch out and shift toward red.
Scientists can measure these tiny color shifts very precisely. By studying the pattern of shifts over time, they can work out how many planets are tugging on the star, how massive those planets roughly are, and how long each orbit takes. The radial velocity method is especially good at measuring a planet’s mass, which is why we have a good mass estimate for Teegarden’s Star d even though so much else remains unknown.
The system now has three known planets in total. Teegarden’s Star d is the most recently confirmed of the three.
Just How Far Is 12.5 Light-Years?
A light-year is the distance light travels in one year — about 9.46 trillion kilometres. That is an almost impossible number to picture. At 12.5 light-years, Teegarden’s Star d is so far away that even the fastest spacecraft ever built by humans would take tens of thousands of years to reach it.
Light leaving that star right now will take 12.5 years to arrive at Earth. So when astronomers observe the system today, they are seeing it as it was 12.5 years ago. You can explore distances like this using our Distance and Travel Time tool, which lets you compare how long different journeys across space would really take.
Even so, 12.5 light-years is close in cosmic terms. Most stars in our galaxy are thousands of light-years away. Teegarden’s Star sits among a small cluster of nearby stars, and you can see how it fits into the wider picture on our Cosmic Map.
Teegarden’s Star d is a cold, Earth-sized world circling a small red star very close to home — at least by the standards of the universe. We know surprisingly little about it so far, and that is part of what makes it interesting. As telescopes improve and scientists gather more data, this quiet neighbor may have more to tell us about how common Earth-sized planets really are.