We know that space is full of mystery. To add to the intrigue, astronomers recently discovered an ancient solar system very different from our cosmic home.
Some 90 light-years away, researchers have spotted a white dwarf star more than 10 billion years old – that is, the remaining hot core of a dead sun-like star – which is surrounded of a graveyard of broken pieces of planets, called planetesimals. The faint star attracted debris from these objects. But this solar system is unlike anything around us. It is full of elements like lithium and potassium. Above all, no planet in our solar system has such a composition.
Why was this ancient solar system in our early Milky Way galaxy so different? How was it enriched with these materials, which were rare at the time?
“It’s a complete mystery,” Abbigail Elms, a PhD student at the University of Warwick who studies white dwarfs, told Mashable. The research was published this week in the scientific journal Royal Astronomical Society Monthly Notices.
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As shown above, this solar system is Old. This means that the white dwarf (called WDJ2147-4035) and its surrounding solar system formed and died before the sun and Earth were even born. In fact, pieces of ancient planets around WDJ2147-4035 are oldest planetesimals ever found in our galaxy around a white dwarf, Elms noted.
How do astronomers know what this archaic solar system was made of?
They discovered this white dwarf, and another of a similar age, using an observatory in space called Gaia. In orbit around the sun, this distant spacecraft maps the stars and galaxies of the cosmos. After spotting these white dwarfs, the researchers then turned to an instrument called “X-Shooter”, located at high altitude in Chile, to detect what is and is not present in the atmospheres of stars (X- Shooter is a type of an extremely valuable astronomical tool called a “spectrometer”). In WDJ2147-4035, they found that chemicals like lithium, potassium, and sodium had accumulated — or been pulled by gravity and collected around — the ancient star. White dwarfs are made of hydrogen or helium, so the rocky remains of the planets were responsible for supplying the other unique elements, the researchers concluded (by running simulations of the evolution of this solar system).
An artist’s conception of pieces of planets (planetsimals) orbiting white dwarf stars.
Credit: University of Warwick / Mark Garlick
Interestingly, the other white dwarf (WDJ1922+0233) they discovered was very different from the mysterious one. It’s more familiar. They determined that this star had carried planetary debris similar to Earth’s rocky crust. So while one solar system remains an anomaly, the other shows that Earth isn’t so unique in the cosmos: there are other solar systems that look a bit like it.
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Both of these solar systems, however, are filled with graveyards of ancient planets. More than 95% of stars, like the sun, evolve into white dwarfs. Towards the end of their lives, they transform into colossal red giant giants, destroying or disrupting nearby objects. When our sun expands, it engulfs planets like Mercury, Venus, and possibly even Earth, before shedding its outer layers. The red giants will leave behind relics of shattered planets and moons. The remaining star itself will be a white dwarf.
It is our cosmic destiny. But not for a long, long time.
“Our sun will evolve into a white dwarf in about 5 billion years,” said Elms.
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