The primordial process that turns enormous clouds of cosmic dust into newborn planets over millions of years has been observed directly for the first time.
Astronomers caught sight of a planet in the making around a young star in the neighbourhood of Taurus, 450 light years from Earth.
The discovery is a boon for scientists who have never before had a real star system against which they can check theories of how the universe came to be dotted with different worlds.
“This is our first chance to watch the planet formation process happening,” said Stephanie Sallum, a graduate student at the University of Arizona. “We can go and look at this and do more detailed studies now, to try to understand how planets are built.”
Although nearly 1,900 alien worlds have been spotted beyond our solar system, none are still forming. And with no growing planets to gaze at, scientists can only compare their models for how planets are born with the end results, such as fully mature rocky worlds and gas giants.
That leaves an enormous gap in astronomers’ understanding. The latest ideas on planetary formation put broad margins on the time the process takes, ranging from 1m to 10m years. What happens between the start and finish is hazy. As Zhaohuan Zhu, an astrophysicist at Princeton University, puts it: “Little is known about how microscopic dust particles can grow 14 orders of magnitude to become a giant planet.”
What is known is that particles left over from the dusty disc that surrounds a newborn star coalesce and coalesce until eons later, a nascent planet takes shape. It grows as material from its own dusty disc rains down on the surface, forming a huge sphere under its own gravity.