A Key Mystery Of How Planets Form May Have Been Solved

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How planets form remains a bit of a mystery. For one thing, we still aren’t sure how material builds up into a planet. We’re also not sure how material actually survives around a star without being eaten.

A new study may provide an answer to the latter. Published in The Astrophysical Journal Letters, a team led by the University of Exeter in the UK has seen a “dust trap” around a distant star, which may explain how planet material survives.

“Dust trapping is one potential solution to a major stumbling block in our theories of how planets form,” Professor Stefan Kraus, the study’s lead author, said in a statement.

To understand what’s going on, take a look at the following image captured by the Atacama Large Millimeter Array (ALMA) in Chile.

Kraus et al/ALMA

This is a young star called V1247 Orionis that is in the process of forming a planetary system. This is not the first such system we’ve seen, but it does have an unusual trait.

Note, first, that the star (which is right in the middle) is surrounded by a hot ring of dust and gas in red. It’s thought that drag in the disk should eventually cause the material to be eaten by the star so that it never gives rise to planets at all. This is known as radial drift.

In the top left of the image, though, you’ll notice a crescent band. Between this and the red disk, there’s a sort of gap in the disk.

What’s going on here is that a planet is likely orbiting in this gap, 100 times further than Earth orbits our Sun, having swept up material there. Its motion is creating areas of high pressure either side of its path, like a ship going through water.

This creates protection regions, dust traps (the crescent band), which can exist for millions of years. This gives the material time to clump together and form a planet before it is eaten by a star.

How that first planet formed, well, the authors haven't covered that. But this exciting research opens the door to working out how planetary systems come to be, rather just being devoured.

“The superb resolution of our ALMA image reveals intriguing substructure in the dust trap and provides for the first time the opportunity to confront competing theories of vortex formation with detailed observational evidence,” the team wrote in their paper.

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