The first rocky planets may have formed just 100 million years after the Big Bang, scientists say — and they could have been surprisingly Earth-like

The first planets in the universe may have appeared far sooner than astronomers once imagined.

A new computer simulation suggests that rocky, potentially habitable planets could have begun forming only about 100 million years after the Big Bang — a time when the universe was still in its infancy and the first galaxies had not yet fully emerged.

The finding pushes back the possible birth date of rocky planets by billions of years and raises an extraordinary question: could the ingredients needed for life have existed almost from the beginning of the universe?


Researchers say the answer is not that life existed at that time. There is no evidence of that.

Instead, the study suggests that some of the essential raw materials needed to construct rocky worlds may have appeared surprisingly early, concentrated in the debris produced when the universe's first massive stars exploded.

The research was published August 19 in The Astrophysical Journal Letters.

The early universe was not ready to build Earth-like planets

Immediately after the Big Bang, the universe was dominated by hydrogen and helium, along with tiny amounts of other light elements.

Rocky planets require something more.

Elements such as carbon, oxygen and iron are important ingredients in the formation of planets and the chemistry associated with life. Those heavier elements were not produced in significant quantities during the Big Bang itself.

They had to be forged inside stars.

That means the universe first needed generations of stars to form, live and die before enough heavy elements could become available for rocky planets.

For years, astronomers have therefore assumed that terrestrial planets could not have appeared until considerably later in cosmic history.

The new research suggests there may have been an important shortcut.

The explosions that could have changed everything

The researchers focused on the deaths of some of the earliest and most massive stars.

In particular, they modelled an extraordinary type of stellar explosion known as a pair-instability supernova.

These explosions occur under extreme conditions and can destroy a massive star completely, scattering enormous quantities of newly forged elements into surrounding space.

According to the simulations, a single such explosion could release an amount of heavy material equivalent to roughly 100 times the mass of the Sun.

Instead of looking at the average chemical conditions across the young universe, the researchers concentrated on these unusually enriched pockets of stellar debris.

That distinction is important.

The universe as a whole may have contained very little material suitable for making rocky planets. But around the remnants of certain massive stars, the concentration of heavy elements could have been dramatically higher.

Dust from ancient stars may have become planet-building material

The simulations followed what happened after one of these enormous explosions.

As the supernova debris expanded, it mixed with surrounding gas. Eventually, gravity caused part of this material to collapse again.

A new star formed within the enriched cloud.

But the process did not end there.

The young star became surrounded by a disk of gas and dust — the same kind of environment in which planets form around young stars today.

Within that disk, the simulation produced small solid bodies known as planetesimals.

These objects can range from a few metres to several kilometres across and are considered the raw embryos from which planets can eventually grow.

The researchers found that some of these planetesimals formed at distances from their star where liquid water could potentially exist.

That does not mean an ocean-covered Earth was created in the simulation.

It means the basic physical conditions needed to begin assembling a rocky world may have existed extraordinarily early.

Water may have arrived shortly after

The availability of water is another intriguing part of the scenario.

Water is not simply something that appears once a rocky planet forms. It can also be delivered to young planetary systems by icy material and other bodies.

The simulations indicated that water could have become available in the young system relatively soon after the planet-building process began.

This raises the possibility that some of the earliest rocky planets could have acquired at least some of the ingredients associated with habitability.

Again, scientists stress that habitability is not the same thing as life.

A planet can have water and the chemical ingredients needed for life while remaining completely lifeless.

But the discovery changes the timeline for when those ingredients may first have come together.

Could Earth-like worlds have existed before the first galaxies?

This is where the finding becomes particularly striking.

The simulation suggests that rocky planet formation may have started around 100 million years after the Big Bang, potentially before the universe had developed the mature population of galaxies seen today.

That means planetary systems might not have been a late development in cosmic history.

They could have begun appearing while the universe was still undergoing its earliest major transformations.

Astronomer Daniel Whalen of the University of Portsmouth, who led the research, said the simulations point towards the possibility that habitable worlds could have formed billions of years earlier than traditionally expected.

If correct, the result pushes the potential origin of planets — and perhaps the chemical conditions associated with life — much closer to the beginning of cosmic history.

The earliest planets may still be out there

The study raises another fascinating possibility.

What if some of these ancient planetary systems survived?

The star produced in the researchers' simulation had around 70 percent of the Sun's mass.

That is significant because stars of this size can remain active for a very long time.

If such a system formed in the early universe and later became incorporated into a galaxy such as the Milky Way, its planets could potentially still exist today.

Astronomers might even be able to identify such a system by examining its chemical composition.

Ancient stars tend to contain very different proportions of heavy elements compared with younger stars. A planetary system with an unusual chemical fingerprint could therefore provide clues that it originated during a much earlier period of cosmic history.

Finding one would be an extraordinary discovery

Actually detecting one of these ancient planetary systems would be difficult.

Astronomers would first need to identify an exceptionally old star with the appropriate chemical signature. They would then need to determine whether planets orbit it and establish how old the system really is.

But researchers say the possibility is not outside the realm of observation.

If an ancient planetary system survived long enough to become part of the Milky Way, its chemical composition could provide an important record of the universe's earliest planet-forming environments.

Such a discovery would give astronomers something they currently lack: a direct example of a planetary system that formed near the beginning of cosmic history.

The researchers are not finished yet

The new simulation represents an early stage of the investigation.

The researchers are now working to model what happens after planetesimals appear and determine what kinds of planets they could eventually produce.

They also want to investigate other types of supernovae that may have been more common during the universe's earliest period.

Those calculations could reveal whether the process described in the study was an unusual exception or part of a broader pathway for early planet formation.

If other types of stellar explosions can also create sufficiently enriched environments, the number of possible early planetary systems could be much larger than the current simulation suggests.

A new question about the beginning of life

The research ultimately raises a question far bigger than when the first rocky planet formed.

If planets with the right chemical ingredients could emerge just 100 million years after the Big Bang, then the universe may have become chemically capable of supporting complex planetary environments much earlier than previously believed.

That does not tell us when life began.

It does, however, move the starting line.

The ingredients for rocky worlds may have been available almost as soon as the universe had its first generation of stars.

And if some of those ancient planets survived, astronomers may one day be able to search for them — potentially uncovering worlds that began their journey more than 13 billion years ago.

The universe may have been building planets long before it looked anything like the cosmos we know today.