Earth and the other planets in the solar system have been around for longer than previously thought according to new research into shredded asteroids in distant star systems.
A study published today in the journal Nature Astronomy examines some of the oldest stars in the Universe and suggests that stars and planets grow together. It had been thought that planets didn’t form until a star had reached its full size.
The Sun formed 4.6 billion years ago from a cloud of gas with the planets forming around it.
“We have a pretty good idea of how planets form, but one outstanding question we’ve had is when they form,” said Dr Amy Bonsor from Cambridge University’s Institute of Astronomy and the study’s first author. “Does planet formation start early, when the parent star is still growing, or millions of years later?”
The researchers used the Atacama Large Millimeter Array of radio telescopes in Chile to study the atmospheres of white dwarfs—the remains of Sun-like stars after their life cycle has come to an end—in search of the “planetesimals”—the building blocks of planets. “Some white dwarfs are amazing laboratories because their thin atmospheres are almost like celestial graveyards,” said Bonsor.
The white dwarfs studied are special cases because their atmospheres are polluted with heavy elements such as magnesium, iron and calcium, which—say the authors—must have been left there by asteroids left over from planet formation that later crashed into the white dwarfs and melted in their atmospheres.
The process of iron sinking to the core while lighter elements float on the surface is what caused the Earth to have an iron-rich core, according to the paper.
Planet formation is generally believed to begin in a disc of hydrogen, helium and particles of ice and dust orbiting a young star. As the dust particles combine, planetesimals emerge and get larger over time to become asteroids or planets.
This study suggests that planetesimals form almost immediately. “If these asteroids were melted by something that only exists for a very brief time at the dawn of the planetary system then the process of planet formation must kick off very quickly,” said Bonsor. “Our study complements a growing consensus in the field that planet formation got going early, with the first bodies forming concurrently with the star.”
Wishing you clear skies and wide eyes.