Vaporizing asteroids provide critical information on planet formation
We still have a lot to learn about the early years of our solar system. Astronomers rely on other stars for insight into the early years of how stars and their planets are formed because we can’t go back in time.
A team of astronomers recently discovered evidence that stars and planets actually grow up together, forming at the same time in the life of a solar system.
“We have a pretty good idea of how planets form, but one unanswered question is when they form: does planet formation begin early, while the parent star is still growing, or does it happen millions of years later?” Amy Bonsor, an astronomer at Cambridge University in the United Kingdom and the study’s lead author, said in a statement.
Surprisingly, their evidence for planet formation came from an unexpected source: the dead core of a former sun-like star known as a white dwarf. White dwarfs are primarily composed of hydrogen and helium, but they can become “polluted” when an asteroid or other rocky body collides with them. Astronomers can then use the composition of the newly polluted white dwarf to determine what the asteroids were made of.
“Some white dwarfs are amazing laboratories,” Bonsor said, “because their thin atmospheres are almost like celestial graveyards.”
Many of the 200 white dwarfs observed by the team were iron-rich, pointing to iron-rich asteroids. The decay of a radioactive form of aluminum is the most likely source of heat in order to give an asteroid an iron core.
However, this material, known as aluminum-26, can only exist for a little less than a million years — a blink of an eye in the cosmic timescale — before decaying. So, in order for these asteroids to contain as much iron as the astronomers discovered in white dwarfs, they had to have formed relatively early, at the same time as the star itself.
“This is only the beginning,” Bonsor explained. “With each new white dwarf discovered, we can gather more evidence and learn more about how planets form.”
The findings were published in the journal Nature Astronomy on Monday (November 14).
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