First ocean-bearing planets may have emerged almost immediately after the Big Bang

An international team of astrophysicists, including researchers from Russia's Southern Federal University, have reached a surprising conclusion: rocky planets with water could have formed as early as 100 million years after the Big Bang. The findings are published in The Astrophysical Journal Letters.

What Was Previously Believed

Until recently, the prevailing view was that active planet formation began much later—roughly when the Universe had reached half its current age. It was thought that rocky worlds required a sufficient accumulation of heavy elements, a process that took a very long time.

New data change this picture. The first stars ended their short lives in powerful explosions of a particular type of supernova. Such bursts ejected over 100 solar masses of heavy elements into the surrounding space. Gas clouds became locally enriched with metals, and from this material new, less massive and far longer-lived stars were born.

What the Models Showed

The scientists modelled the collapse of a core enriched with heavy elements. As a result, a protoplanetary disk formed around a young, low-mass star, in which planetesimals—precursors to rocky planets—could already emerge. Their total mass reached several Earth masses.

These early disks contained significant amounts of cosmic dust, which gradually coalesced into larger bodies. An important finding was that the water mass fraction in such systems was only slightly lower than in the Solar System. This means that, theoretically, even in the first generation of planets, worlds with oceans could have existed.

Why This Matters

The study significantly shifts the possible timeline for the emergence of conditions suitable for life. If rocky planets with water could exist virtually at the dawn of the Universe, the window for the potential emergence of life turns out to be far wider than previously assumed.

The authors note that low metallicity and the specific chemical composition of the parent star could serve as indicators of its ancient origin. The detection of such systems by future missions—particularly with the PLATO telescope—will allow the hypothesis to be tested in practice.

In Brief

Astrophysicists have shown that planetesimals and rocky planets with substantial amounts of water could have formed as early as 100 million years after the Big Bang—around low-mass stars born in the remnants of ancient supernovae. The water fraction in such early systems was only slightly below solar levels. The discovery revises previous assumptions about when conditions suitable for life first appeared in the Universe.