Looking up at the night sky, it’s easy to forget that we are seeing a history book written in starlight. Many of those points of light are ancient, and some of them are home to worlds that have existed for almost as long as the universe itself. The search for these primordial planets takes us on a journey back in time, offering a glimpse into the earliest eras of cosmic formation. Finding these ancient worlds helps us piece together the story of how planetary systems, including our own, came to be.
Astronomers have identified a handful of these celestial elders, some of which are nearly 13 billion years old. This list of the 12 Oldest Known Planets in the Universe Today is more than just a record book; it’s a testament to the resilience and frequency of planet formation. These worlds have witnessed the majority of cosmic history, from the early assembly of galaxies to the birth and death of countless stars. Their existence pushes the timeline for planet formation back to a surprisingly early epoch in the universe’s evolution.
What Makes a Planet Ancient?
When we talk about the oldest planets, we are typically referring to worlds that formed within the first billion years after the Big Bang. To put that in perspective, our own Sun and Earth are relative newcomers at about 4.6 billion years old. These ancient planets are almost always found orbiting stars that are equally old, known as Population II stars. These stars are metal-poor, meaning they contain very low amounts of elements heavier than hydrogen and helium, which were forged in the cores of the first generations of stars.
The discovery of planets around such stars was a surprise. For a long time, the prevailing theory was that a sufficient amount of “metals” was necessary to form rocky planets. Finding these ancient worlds forced scientists to reconsider the processes of planet formation, suggesting that planets can form under a much wider range of conditions and much earlier than previously thought.
A Glimpse at the 12 Oldest Known Planets in the Universe Today
While the exact ranking can change with new discoveries, the following list highlights some of the most ancient and fascinating worlds confirmed to date. Their ages are staggering, often determined by the age of their host star.
PSR B1620-26 b (Methuselah): Often nicknamed “the oldest known planet,” this world is a true cosmic relic. At approximately 12.7 billion years old, it formed only a billion years after the Big Bang. It orbits a pair of burned-out stars—a pulsar and a white dwarf—in a globular cluster, a dense collection of ancient stars.
Kepler-444 System Planets: The star Kepler-444 is about 11.2 billion years old, and it hosts five terrestrial planets, all roughly the size of Earth or smaller. This discovery was groundbreaking because it proved that Earth-sized planets have been forming for most of the universe’s history.
TOI-561 b: This is a rocky “super-Earth” orbiting one of the oldest known stars in the galactic disk, at about 10 billion years of age. Despite being rocky, it is likely far too hot to host life as we know it, completing an orbit around its star in less than half an Earth day.
Other notable ancient planets include several Jupiter-sized gas giants found in the Milky Way’s halo, orbiting stars like HIP 11952 and BD+20 2457. Each of these systems, often discovered through the radial velocity method that detects a star’s subtle wobble, adds another piece to the puzzle of our cosmic origins.
Why Finding Ancient Planets Matters
You might wonder why astronomers go to such great lengths to find these incredibly distant and old worlds. The significance is profound. Every ancient planet discovered is a data point that helps us answer fundamental questions: How quickly did the first planets form after the Big Bang? Is our solar system’s architecture common or rare? And, perhaps most compellingly, could life have arisen in the ancient universe?
The existence of rocky planets like those in the Kepler-444 system, which formed over 11 billion years ago, suggests that the ingredients for life—rocky worlds with the right conditions—have been present for a very, very long time. It dramatically expands the potential timeline for the development of life in the cosmos.
The Future of Hunting for Ancient Worlds
The hunt for these time-worn travelers is accelerating. Space telescopes like the James Webb Space Telescope (JWST) are revolutionizing this field. With its powerful infrared capabilities, JWST can analyze the atmospheres of exoplanets, including some of the oldest ones we know. By studying the chemical composition of these atmospheres, we might one day find biosignatures—signs of life—on a world that has been around for twice the age of our Sun.
Future missions will also continue to scan the oldest stars in our galaxy and even in nearby dwarf galaxies, pushing the boundaries of how far back in time we can observe planet formation. Each new discovery has the potential to upend our understanding of the cosmic dawn of planets.
In the end, the story of the 12 Oldest Known Planets in the Universe Today is really our origin story, too. They teach us that planet formation is a robust and universal process. These ancient worlds are silent witnesses to the deep past, and by studying them, we connect our own fleeting existence to the vast, epic timeline of the cosmos.