To date, we have found thousands of planets in our galaxy, most with the Kepler telescope, and we have also spotted the very beginnings of planetary formation – giant discs of dust and gas around stars. But we had yet to observe the stages in between, when extremely fine dust forms larger ‘pebbles’ that, over billions of years, eventually coalesce into planets.
Now, one part of that key process has been spotted; a star 450 light-years away that is just 2.5 million years old appears to have an extensive ring of these pebbles circling it. The process of forming planets in our own solar system took 4.5 billion years, meaning this star – called DG Tauri – offers a glimpse into the very beginnings of planetary formation. The findings were presented at the National Astronomy Meeting in Llandudno, Wales.
"The idea is [the pebbles] stick together into asteroids the size of buildings and mountains," Jane Greaves from the University of St Andrews, who led the research, told IFLScience.
Greaves' colleague Anita Richards from the University of Manchester said in a statement that they had already known the star had jets of hot gas from its poles, “a beacon for stars still in the process of forming.” But she added it was “a real surprise to also see a belt of pebbles, with only a fraction of the data we hope to acquire.” The pebbles are thought to each be more than a centimeter in size and span an area hundreds of millions of kilometers wide in two separate bands on either side of the star.
The data was acquired using the e-MERLIN array, a collection of seven telescopes across England that is centered on Jodrell Bank in Cheshire. Using a process known as interferometry, they can mimic the observational power of a much larger telescope.
“The extraordinarily fine detail we can see with the e-MERLIN telescopes was the key to this discovery,” said Greaves.
She noted that the region they observed was as small as the orbit of Jupiter in our own solar system. DG Tauri is 2.5 times larger than our sun, however, so it’s unlikely to form planets in exactly the same positions as ours.
This image created using the e-MERLIN data shows the star and the pebbles that surround it, with the highest density in red. Via J. Greaves / A. Richards / JCBA
The discovery is hugely important, though. Greaves runs an international team called the Planet Earth Building Blocks Legacy e-MERLIN Survey, or PEBBLeS, that will search for such rocky belts around stars using e-MERLIN and the upcoming Square Kilometer Array. Finding more could reveal how often planets form, and her team also hopes to find planets like Earth taking shape around sun-like stars. This would indicate whether habitable worlds like our own are rare or commonplace in the universe.
"The hunt is on for Earth-like planets," said Greaves.