Planets like Mars, Venus and our own are made up primarily of silicate rocks and have an iron core and a thin veneer of water and life. Planets formed in the early days of the universe are likely different — or consisted of graphite, carbides and diamond, according to new research.

Since 2005, astronomy has been abuzz with news of theoretical planets known as carbon planets, also called diamond planets. Discussions continued when Jupiter was proposed back in 2004 to have formed a carbon-filled core.

In the new study, Harvard astronomers suggested that the first likely habitable worlds might have been of this kind — and these planets can be found through searching a rare kind of stars.

"This work shows that even stars with a tiny fraction of the carbon in our solar system can host planets," said lead author and graduate student Natalie Mashian, adding that there is reason to believe that alien life as well as that in the early days of the universe are carbon-based, just like life on Earth.

In the primordial universe, it was mostly hydrogen and helium and none of carbon, oxygen and other elements needed by life. Only later on when the early stars exploded as supernovae did life-supporting planets formed.

In this research, the team analyzed old stars called carbon-enhanced metal-poor (CEMP) stars, which are anemic stars containing a mere one-hundredth-thousandth of the iron of the sun. This means that they came into being prior to heavy elements massively seeding deep space.

This effectively makes them fossils from the early universe — offering a look into how planetary systems began.

With the lack of iron and other heavy elements abundant in the sun, CEMP stars maintain more carbon than expected of their age. This potentially influences formation of planets, as carbon dust grains group together to create tar-black habitats.

From afar, a carbon planet is quite difficult to distinguish from Earth-like systems. Their sizes and masses would be quite similar, but astronomers would need to probe the former’s atmosphere to know it more intimately, such with carbon monoxide and methane enveloping this strange world.

Using the transit technique, planets around these fossil stars can be sought out, the researchers argued. This technique searches for the tiny dip in a distant star’s light as an unknown planet passes in front. A large portion of identified exoplanets — planets that orbit other suns — were detected through it.

The findings are detailed in the journal Monthly Notices of the Royal Astronomical Society.

A separate study from Cornell University considered dying stars a great place to hunt for alien life. When they reach old age and start to run out of fuel, most stars swell up to hundreds of times their typical size, engulfing nearby planets. Even planets around dying stars, however, can still sustain life, according to the research.

The hope is that such worlds could be livable in the distant future and maybe even pave way to life just like Earth — a source of optimism for life to also flourish and continue in the long term.

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