Scientists Have Found The Oldest Known Earth-Sized Planet in The Milky Way

For years, astronomers have operated under a simple assumption: Earth-like planets, capable of supporting life, are a relatively new phenomenon in the Universe.

But what if that assumption is wrong?

A team of researchers has discovered what they believe to be the oldest Earth-sized planet ever found in the Milky Way, orbiting a star a staggering 11.2 billion years old—more than twice the age of our Solar System.

This discovery is more than just a record-breaking find. It challenges long-held theories about planetary formation and raises a tantalizing question: Could ancient lifeforms have evolved billions of years before us?

A Star System Older Than Our Imagination

The planetary system in question is known as KOI-3158, located approximately 117 light-years away.

NASA’s Kepler telescope first observed the system, which contains five planets similar in size to Earth.

The most Earth-like among them, known as K3158.05, has become a focal point of intense scientific interest.

To put its 11.2-billion-year age into perspective, our own Solar System is less than 5 billion years old.

That means these planets existed before Earth was even formed—when the Universe itself was less than 20% of its current age.

The Metal-Poor Paradox

What makes KOI-3158 even more fascinating is that its star is incredibly poor in metals.

Typically, planets like Earth form around metal-rich stars, which provide the necessary heavy elements for rocky planets.

This discovery contradicts a fundamental assumption in planetary science.

As Tiago Campante, an asteroseismologist from the University of Birmingham who led the study, explained:

“That implies that Earth-sized planets may have readily formed at earlier epochs in the Universe’s history when metals were more scarce.”

This means that Earth-like planets could have formed throughout the entire history of the Universe, vastly expanding the potential for ancient extraterrestrial life.

A Compact System Unlike Any Other

Another unusual feature of KOI-3158 is how tightly packed its planets are. Unlike our Solar System, where planets are spaced out across vast distances, the planets in KOI-3158 have incredibly short orbits.

The closest planet completes an orbit in less than 10 days, meaning that an entire year on this world would pass in about a week.

This compact arrangement suggests that the planetary system evolved under completely different conditions than our own.

It raises new questions about planetary stability, habitability, and how such an ancient system managed to remain intact for over 11 billion years.

What If Intelligent Life Existed Before Us?

Here’s where things take an even more dramatic turn.

If Earth-sized planets have existed for most of the Universe’s history, then the possibility of life evolving billions of years before us becomes a real consideration.

As Eric Mack from Gizmag puts it:

“If the conditions for life exist on such ancient planets, those lifeforms may have had a few billion years head start on us to become intelligent and even technologically advanced. They may have even had enough time to evolve, develop advanced technology, and wipe themselves out in a scenario fit for many an apocalyptic science fiction epic. Heck, they may have come and gone before our Solar System was even born.”

This raises profound philosophical and scientific questions. Did intelligent civilizations rise and fall before Earth even existed?

Could traces of their existence still be lurking somewhere in the cosmos?

The Hunt for More Answers

Campante’s research has now been submitted to The Astrophysical Journal, but this discovery is only the beginning.

Follow-up observations from other telescopes will be critical in determining the exact nature of these planets and whether they may have once supported life.

One of the most exciting developments is the James Webb Space Telescope, launched in 2021.

This powerful successor to Hubble is capable of analyzing the atmospheres of distant exoplanets, providing crucial insights into their potential habitability.

Meanwhile, NASA’s Kepler telescope, which first discovered KOI-3158, is back online.

After a temporary shutdown in 2013, NASA engineers found an innovative way to stabilize it using solar radiation pressure—essentially using sunlight to keep the telescope steady.

Despite its age, Kepler continues to discover new Earth-sized planets, fueling hope that even more ancient worlds will be found.

A New Era of Planetary Discovery

This discovery has rewritten the rules of planetary formation and expanded our understanding of the Universe’s potential for life.

For decades, astronomers believed that metal-rich stars were necessary for rocky planets.

Now, KOI-3158 proves that Earth-like worlds could have formed even in the earliest days of the cosmos.

The implications are staggering:

If Earth-like planets are this old, they could have supported life billions of years before Earth formed.
If intelligent civilizations arose that long ago, they might have explored, colonized, or even disappeared before we had the chance to detect them.
The search for extraterrestrial life must now consider far older star systems than previously thought.

With every new discovery, we inch closer to answering one of humanity’s greatest questions: Are we alone in the Universe?

Or have other civilizations already come and gone, leaving behind only cosmic echoes of their existence?

For now, the search continues.

But one thing is clear—we are no longer looking for just young Earths.

The ancient ones may hold the biggest secrets of all.